Phase characteristic calibration device and phase characteristic calibration method

Abstract

To provide a phase characteristic calibration device that eliminates the need for a continuous wave (CW) light source from an interferometer and has high cost effectiveness.SOLUTION: A phase of a multi-tone signal for calibration is measured by using an electro-optical sampling method. In an interferometer 110, short pulse light is input to a first optical path including a variable delay device 4 and to a second optical path not including the variable delay device, and the short pulse light output from the first optical path and the short pulse light output from the second optical path are made to interfere with each other and are output as interference light. A light receiver 106 detects an intensity of the interference light and outputs it as an interference signal, and a frequency divider 107 frequency-divides the interference signal. A multi-tone signal obtained by an electro-optical sampling unit 30 or the like is sampled according to an output from the frequency divider to correct a multi-tone signal. The interferometer includes a light BPF 108 that expands a pulse width of at least one of the short pulse light output from the first optical path and the short pulse light output from the second optical path, so as to obtain interference light.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for calibrating phase characteristics, and more particularly to an apparatus and method for calibrating the phase characteristics of a millimeter wave band signal measuring instrument or a millimeter wave band signal generator. [Background technology]

[0002] In order to improve the transmission speed of wireless communication, communication methods that use broadband modulated signals in the millimeter wave, submillimeter wave, and terahertz wave bands, which have higher carrier frequencies than conventional ones, are being considered. Hereinafter, the millimeter wave, submillimeter wave, and terahertz wave bands will be collectively referred to as the millimeter wave band.

[0003] Generally, when frequencies become high and bands become wide, the phase frequency characteristics of the frequency conversion section (up-converter or down-converter) of a millimeter-wave band signal generator or a millimeter-wave band signal measuring instrument cannot be ignored, so it is important to calibrate the phase characteristics of the frequency conversion section. Also, in the multi-level quadrature amplitude modulation method, which has high spectral efficiency, even a small phase error can cause degradation of the transmission characteristics, so accurate calibration of the phase characteristics is required.

[0004] Usually, a test device for testing the performance of a millimeter-wave band receiver is equipped with a millimeter-wave band signal generator for generating a measurement signal, and a test device for testing the performance of a millimeter-wave band transmitter is equipped with a millimeter-wave band signal measuring device for measuring a measured signal. It is easy to connect these millimeter-wave band signal generator and millimeter-wave band signal measuring device and calibrate the frequency characteristics of both at the same time. However, in order to accurately evaluate the millimeter-wave band receiver under test, it is necessary to calibrate the phase frequency characteristics of only the millimeter-wave band signal generator and generate an accurate millimeter-wave band modulated signal (measurement signal) with little phase error and input it to the millimeter-wave band receiver. In addition, in order to accurately evaluate the millimeter-wave band transmitter under test, it is necessary to calibrate the phase frequency characteristics of only the millimeter-wave band signal measuring device and accurately measure the millimeter-wave band modulated signal (measurement signal) output from the millimeter-wave band transmitter.

[0005] Electro-optic sampling is a method for generating a millimeter-wave calibration signal and measuring its phase frequency characteristic in order to calibrate the phase characteristics of a millimeter-wave signal measuring instrument or a millimeter-wave signal generator.

[0006] FIG. 1 is a conceptual diagram for explaining an electro-optic sampling method used when measuring the time waveform of an electric pulse as a calibration signal. A pulse light emitted from a short pulse light source (not shown) is branched, and one of the branched pulse lights is input to a DUT (Device Under Test) 201 such as a photodiode, and the other pulse light is input as a sampling pulse light to an electric field detector 202 such as an electro-optic crystal via an optical variable delayer 204. The DUT 201 outputs an electric pulse in the millimeter wave band according to the input pulse light, and this electric pulse is input to the electric field detector 202. The electric field detector 202 detects the electric field intensity of the electric pulse according to the sampling pulse light based on the electro-optic effect. Then, the optical variable delayer 204 changes the delay amount (delay time) of the sampling pulse light, thereby detecting the electric field intensity of the electric pulse while shifting the time at which the millimeter wave band electric pulse is sampled. In this way, the time waveform of the millimeter wave band electric pulse can be measured.

[0007] FIG. 2(a) is a timing chart of the signals in FIG. 1. The first diagram from the top of FIG. 2(a) shows a sampling pulse light output from a short pulse light source (not shown), which is a pulse light with a repetition frequency f (period: 1 / f). The second diagram of FIG. 2(a) shows an electric pulse, which is a signal to be measured output from the DUT 201, which is an electric pulse with a repetition frequency f. The third diagram of FIG. 2(a) shows a signal output from the optical variable delay device 204, which is a sampling pulse light delayed by Δt from the sampling pulse light. As shown in the fourth diagram of FIG. 2(a), the electric field detected by the electric field detector 202 is an electric field at a time corresponding to the delayed sampling pulse light in the electric pulse (i.e., a time delayed by Δt from the sampling pulse light).

[0008] FIG. 2(b) is a diagram showing how the waveform of an electric pulse is measured by measuring the electric field of the electric pulse each time the delay time Δt is changed by the optical variable delay device 204 from Δt1, Δt2, . . . , Δtn.

[0009] In conventional phase characteristic calibration devices, in order to calibrate the phase characteristics of a millimeter wave band signal measuring instrument or a millimeter wave band signal generator, the phase of a millimeter wave band tone signal serving as a calibration signal is measured by measuring the time waveform of the millimeter wave band signal using an electro-optic sampling method (see, for example, Patent Document 1).

[0010] <First configuration example> Fig. 27 shows a first configuration example of a conventional phase characteristic calibration device. The conventional phase characteristic calibration device 1000A calibrates the phase characteristic of a downconverter (frequency conversion section 72, intermediate frequency signal conversion section 73) of a millimeter wave band signal measurement section 70 that performs frequency conversion (downconversion) and measures a signal to be measured. For this purpose, the phase characteristic calibration device 1000A includes a short pulse light source 2, an optical branching section 3, an optical variable delay section 4, a calibration signal generation section 20, a synchronization processing section 5, an electro-optic sampling section 30, a lock-in detection section 40, a three-tone phase difference measurement section 50, and a phase correction value calculation section 55. Each component shown in Fig. 27 will be described below.

[0011] A short pulse light source 2 outputs a short pulse light P1 at a predetermined repetition frequency. The short pulse light P1 output from the short pulse light source 2 is branched by an optical branching device 3 into two short pulse lights P2 and P3, which are respectively input to an optical variable delay device 4 and a synchronization processing device 5. The optical variable delay device 4 continuously changes the delay time of the light by mechanically moving the position of a mirror 4a.

[0012] The calibration signal generating section 20 includes a three-tone intermediate frequency signal generating section 10, a reference signal modulating section 17, a frequency converting section 21, and a local signal generating section 22. The three-tone intermediate frequency signal generating section 10 includes intermediate frequency signal generators 11a to 11c and an adder 15, in which the intermediate frequency signal generators 11a to 11c generate sine waves of different frequencies with a predetermined phase difference, and the adder 15 adds the three sine waves to generate a three-tone intermediate frequency signal S 10 The output is as follows:

[0013] The reference signal modulation section 17 includes a reference synchronization signal generator 16, a reference signal generator 18, and a modulator 19. When the switches SW11 and SW12 are set to the lower side in FIG. 27, the reference signal generator 18 receives the reference synchronization signal S 16 According to the above, a reference signal S with a frequency lower than that of each of the three sine waves is 18 The modulator 19 generates a three-tone intermediate frequency signal S 10 Let S be the reference signal. 18 and modulating the modulated three-tone intermediate frequency signal S 19 to the frequency conversion unit 21. When the switches SW11 and SW12 are set to the upper side in FIG. 27, the modulator 19 is bypassed and the 3-tone intermediate frequency signal S 10 is sent to the frequency conversion unit 21.

[0014] The frequency conversion unit 21 converts a CW (Continuous Wave) local oscillator signal S from a local oscillator signal generation unit 22. 22 Three-tone intermediate frequency signal S 19 or S 10 is frequency converted (up-converted) to a millimeter wave frequency, and the calibration signal S 20 The output is as follows:

[0015] The synchronization processor 5 generates a three-tone intermediate frequency signal S 10 and the local oscillator signal S 22 and the repetition frequency of the short pulse light source 2, a millimeter wave calibration signal S synchronized with the repetition frequency of the short pulse light source 2 is generated. 20Specifically, the synchronization processing unit 5 synchronizes the local oscillator signal S output from the local oscillator signal generating unit 22. 22 The local signal generating unit 22 and the intermediate frequency signal generators 11a to 11c are controlled so that the frequency of the calibration signal S and the frequency of each of the sine waves output from the intermediate frequency signal generators 11a to 11c are integer multiples of the repetition frequency of the short pulse light source 2. 20 The repetition frequency of this pulse is an integer multiple of the repetition frequency of the short pulse light source 2.

[0016] When the switches SW11 and SW12 are set to the lower side in FIG. 27 and the switches SW1 and SW2 are set to the upper side in the same figure, the calibration signal S 20 The phase difference is measured.

[0017] The electro-optic sampling unit 30 includes an electro-optic crystal 31, a polarization splitter 32, and a photodetector 33. The calibration signal S 20 The electric field S is applied to the electro-optic crystal 31, and the short pulse light P4 from the variable optical delay device 4 is input to the electro-optic crystal 31 via the polarization separator 32, and the short pulse light reflected at the tip of the electro-optic crystal 31 is input to the optical receiver 33 via the polarization separator 32. When an electric field is applied to the electro-optic crystal 31, the polarization of the reflected light from the electro-optic crystal 31 changes due to the electro-optic effect, and the polarization change of the reflected light is detected by the polarization separator 32 and the optical receiver 33. An electric signal S 30 is proportional to the electric field applied to the electro-optic crystal 31 and also to the optical power of the short pulse light P4. 30 is input to the lock-in detection unit 40.

[0018] The lock-in detection section 40 includes a reference signal generator 41, a phase shifter 42, a modulator 44, and a low-pass filter 45. The reference signal generator 41 receives the reference synchronization signal S 17 According to the above, the reference sync signal S 17 A reference signal S, which is a sine wave of the same frequency as 41The phase shifter 42 generates the reference signal S in the calibration signal sampled by the electro-optic sampling unit 30 in the modulator 44. 18 and the phase of the reference signal S 41 The reference signal S 41 Adjust the phase of the reference signal S 42 The modulator 44 outputs the electrical signal S from the electro-optic sampling unit 30. 30 Let S be the reference signal. 42 and the low-frequency components are extracted by a low-pass filter 45.

[0019] The three-tone phase difference measuring section 50 includes phase detection sections 51a to 51c and a phase difference calculation section 52. The phase detection section 51a detects the electrical signal S 30 The phase detector 51b and the phase detector 51c detect the phase of the second tone and the third tone, respectively. The phase difference calculator 52 calculates the second derivative of each of the three tones and outputs the phase difference measurement result S 50 Specifically, the above process is performed to output the calibration signal S 20 The frequency of the three tones is changed and repeated to measure the second derivative of the phase over a predetermined frequency range. The frequency characteristic of the phase can be obtained by integrating the second derivative of the phase twice. 50 is output from the phase difference calculation unit 52.

[0020] When the switches SW11 and SW12 are set to the upper side in FIG. 27, the switches SW1 and SW2 are set to the lower side in the same figure, and the switches SW3 and SW4 are set to the upper side in the same figure, the calibration signal S 20 The phase difference is measured.

[0021] The millimeter wave band signal measuring unit 70 includes a local oscillator signal generating unit 71, a frequency converter 72, an intermediate frequency signal converter 73, and a phase corrector 74. The frequency converter 72 converts the CW local oscillator signal S 71 Using the millimeter wave calibration signal S20 The local oscillator signal S is frequency converted (down-converted) to an intermediate frequency signal. 71 does not necessarily need to be synchronized with the short pulse light P1, but in the first configuration example, the local oscillator signal S 71 The synchronization processing unit 5 controls the local signal generating unit 71 so that the frequency of the first intermediate frequency signal becomes an integer multiple of the repetition frequency of the short pulse light source 2. The intermediate frequency signal converting unit 73 may include a frequency converter that converts the first intermediate frequency signal into a second intermediate frequency signal.

[0022] The output signal S from the intermediate frequency signal conversion unit 73 of the millimeter wave band signal measurement unit 70 70 is input to the three-tone phase difference measuring unit 50 via the switch SW4 and the switch SW2, and the electrical signal S 30 Similarly to the phase difference measurement in , the phase detection units 51a to 51c detect the phases of the three tones, and the phase difference calculation unit 52 calculates the second order differential of the phases of the three tones to obtain the calibration signal S 20 The frequency of the three tones is changed and repeated, and the second derivative of the phase is integrated twice to obtain the frequency characteristic of the phase. 50' will be output.

[0023] The calibration method is as follows. First, the switches SW11 and SW12 are set to the lower side in FIG. 27, and the switches SW1 and SW2 are set to the upper side in the same figure. 20 is input to the electro-optic sampling unit 30 and measured. 20 Phase difference measurement result S 50 From the calibration signal S 20 The frequency characteristic of the calibration signal S is obtained. Next, the switches SW11 and SW12 are set to the upper side in the figure, the switches SW1 and SW2 are set to the lower side in the figure, and the switches SW3 and SW4 are set to the upper side in the figure. 20 is input to the millimeter wave band signal measuring unit 70 and the frequency converted output signal S 70 Phase difference measurement result S 50' to the output signal S of the millimeter wave band signal measuring unit 70 70 The frequency characteristic of the calibration signal S 20and the frequency characteristic of the output signal S from the millimeter wave band signal measuring unit 70. 70 The frequency characteristics of the downconverter (frequency conversion units 72, 73) of the millimeter wave band signal measuring unit 70 are obtained from the frequency characteristics of the downconverter and the phase correction value calculating unit 55. The phase correction value calculating unit 55 calculates the frequency characteristics of the downconverter over a predetermined frequency range and outputs them to the phase correction unit 74 of the millimeter wave band signal measuring unit 70.

[0024] The measured signal S transmitted from the millimeter wave band signal transmitting unit 60 60 When measuring, the switches SW3 and SW4 are set to the lower side in FIG. 27. The millimeter wave band signal transmitting section 60 up-converts an intermediate frequency signal generated by an intermediate frequency signal generating section 61 using a local signal generating section 62 and a frequency converting section 63 to generate a signal to be measured S 60 The measured signal S 60 is input to the millimeter wave band signal measuring unit 70 via the switch SW3, and is down-converted by the frequency conversion unit 72 and the intermediate frequency signal conversion unit 73 to produce an output signal S 70' is input to the phase correction unit 74. The phase correction unit 74 divides it by the frequency characteristic of the downconverter of the millimeter waveband signal measuring unit 70 (if only the phase is to be corrected, the phase characteristic of the frequency conversion units 72, 73 of the millimeter waveband signal measuring unit 70 is subtracted), thereby obtaining a measurement result in which the frequency characteristics of the frequency conversion units 72, 73 of the millimeter waveband signal measuring unit 70 have been corrected.

[0025] <Second configuration example> 28 shows a second configuration example of a conventional phase characteristic calibration device. The conventional phase characteristic calibration device 1000B calibrates the phase characteristics of the downconverter (frequency conversion unit 72, intermediate frequency signal conversion unit 73) of the millimeter wave band signal measurement unit 70 by using a four-tone signal as a calibration signal. For this purpose, the phase characteristic calibration device 1000B includes a short pulse light source 2, an optical splitter 3, an optical variable delay unit 4, a calibration signal generation unit 20B, a synchronization processing unit 5, an electro-optic sampling unit 30, a multi-tone signal separation unit 40B, a multi-tone phase difference measurement unit 50B, and a phase correction value calculation unit 55. The phase characteristic calibration device 1000B according to the second configuration example is different from the first configuration example in the configurations of the calibration signal generation unit 20B, the multi-tone signal separation unit 40B, and the multi-tone phase difference measurement unit 50B, and the other configurations are the same as those of the first configuration example. The same configurations are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0026] Calibration signal generating section 20B includes multi-tone intermediate frequency signal generating / reference signal modulating section 10B, a multi-tone intermediate frequency signal generating section 25, a frequency converting section 21, and a local signal generating section 22. Multi-tone intermediate frequency signal generating / reference signal modulating section 10B includes intermediate frequency signal generators 11a-11d, reference signal generators 12a, 12b, 90 degree phase shifters 14a, 14b, modulators 13a-13d, an adder 15, and a reference synchronization signal generator 16.

[0027] The intermediate frequency signal generators 11a to 11d generate four-tone intermediate frequency signals S1 to S4, which are repetitive signals (e.g., sine waves) having different frequencies and a predetermined phase difference. The reference synchronization signal generator 16 generates a reference synchronization signal S 16 ,S 17 The reference signal generators 12a and 12b generate a reference synchronization signal S from a reference synchronization signal generator 16. 16The 90-degree phase shifters 14a and 14b generate orthogonal reference signals S6 and S8 having the same frequency as the reference signals S5 and S7 and a phase difference of 90 degrees. The modulators 13a to 13d modulate the intermediate frequency signals S1 to S4 with the reference signals S5 and S7 or the orthogonal reference signals S6 and S8, respectively, and combine them in an adder 15 to generate a multi-tone intermediate frequency signal S 10 The reference signals S5, S7 and the orthogonal reference signals S6, S8 are orthogonal to each other in all combinations.

[0028] The multi-tone intermediate frequency signal generating section 25 includes intermediate frequency signal generators 26a to 26d and an adder 27. The intermediate frequency signal generators 26a to 26d generate four-tone intermediate frequency signals S 11 ~S 14 The adder 27 generates the intermediate frequency signal S 11 ~S 14 are combined to generate a multi-tone intermediate frequency signal S 15 The following is output.

[0029] When the switches SW10 and SW1 are set to the upper side in FIG. 28, the frequency conversion unit 21 converts the local oscillator signal S 22 Using the multi-tone intermediate frequency signal S 10 is up-converted to the millimeter wave band to produce the calibration signal S 20 The calibration signal S 20 is sent to the electro-optic sampling unit 30 via the switch SW1. When the switches SW10 and SW1 are set to the lower side in the figure and the switch SW3 is set to the upper side in the figure, the frequency conversion unit 21 receives the local oscillation signal S 22 Using the above, the multi-tone intermediate frequency signal S from the multi-tone intermediate frequency signal generating unit 25 is generated. 15 is up-converted to the millimeter wave band to generate the second calibration signal S 21 The second calibration signal S 21 is sent to the millimeter wave band signal measuring unit 70 via the switch SW1 and the switch SW3.

[0030] The multi-tone signal separation unit 40B includes reference signal generators 41a to 41b, phase shifters 42a to 42b, 90-degree phase shifters 43a to 43b, modulators 44a to 44d, and low-pass filters 45a to 45d. The reference signal generator 41a receives the reference synchronization signal S 17 According to the above, a reference signal S5, which is a sine wave having the same frequency as the reference signal S5, is 40 The phase shifter 42a generates the calibration signal S sampled by the electro-optic sampling unit 30 in the modulator 44a. 20 The phase of the reference signal S5 in 40 The reference signal S 40 Adjust the phase of the reference signal S 42 The output is as follows:

[0031] The modulator 44a receives the electrical signal S from the electro-optic sampling unit 30. 30 Let S be the reference signal. 42 The output of the phase shifter 42a is input to a modulator 44b via a 90-degree phase shifter 43a, and the modulator 44b converts the electrical signal S 30 Let S be the reference signal. 42 and a reference signal S 43 and the low-frequency components are extracted by low-pass filter 45b.

[0032] The reference signal generator 41b receives the reference synchronization signal S from the reference synchronization signal generator 16. 17 According to the above, a reference signal S7, which is a sine wave having the same frequency as the reference signal S7, is 41 The phase shifter 42b generates the calibration signal S sampled by the electro-optic sampling unit 30 in the modulator 44c. 20 The phase of the reference signal S7 in 41 The reference signal S 41 Adjust the phase of the reference signal S 44 The output is as follows:

[0033] The modulator 44c receives the electrical signal S from the electro-optic sampling unit 30. 30 Let S be the reference signal. 44 The output of the phase shifter 42b is input to a modulator 44d via a 90-degree phase shifter 43b, and the modulator 44d converts the electrical signal S 30 Let S be the reference signal. 44 and a reference signal S 45 The reference signal S is modulated by the low-pass filter 45d and the low-frequency components are extracted. 42 ~S 45 are mutually orthogonal in all combinations. 30 The four-tone signals that have passed through the low-pass filters 45a to 45d are sent to the multi-tone phase difference measuring unit 50B via the switches SW21 to SW24.

[0034] The multi-tone phase difference measuring unit 50B includes phase detection units 51a to 51d and a phase difference calculation unit 52. The phase detection unit 51a detects the electrical signal S 30 Similarly, the phase detectors 51c, 51b, and 51d detect the phase of the first tone of the four tones in the electrical signal S 30 The phase difference calculation section 52 calculates the second derivative of each of the phases of the four tones and calculates the calibration signal S 20 The frequency of the four tones is changed and the measurement of the second derivative of the phase is repeated. The second derivative of the phase is integrated twice to obtain the frequency characteristic of the phase. The phase difference measurement result S 50 The output is as follows:

[0035] The output signal S from the millimeter wave band signal measuring unit 70 70 When measuring the phase difference between the multi-tone intermediate frequency signal S generated by the multi-tone intermediate frequency signal generating unit 25 in the calibration signal generating unit 20B, the switches SW10, SW1, SW21, SW22, SW23, and SW24 are set to the lower side in FIG. 28, and the switches SW3 and SW4 are set to the upper side in the same figure.15 is sent to the frequency converter 21 via the switch SW10 and up-converted to a second calibration signal S 21 A second calibration signal S 21 is input to the millimeter wave band signal measuring unit 70, and the output signal S from the intermediate frequency signal converting unit 73 of the millimeter wave band signal measuring unit 70 is 70 is input to the phase detection units 51a to 51d of the multi-tone phase difference measurement unit 50 via the switches SW4 and SW21 to 24, and the phases of the four tones are detected. Then, the phase difference calculation unit 52 calculates the second derivative of each of the phases of the four tones and outputs the second calibration signal S 21 The frequency of the four tones is changed and the measurement of the second-order differential value of the phase is repeated. The second-order differential of the phase is integrated twice to obtain the frequency characteristic of the phase. 50' The output is as follows:

[0036] The calibration method is as follows. First, the switches SW10, SW1, and SW21 to 24 are set to the upper side in FIG. 20 is input to the electro-optic sampling unit 30 and measured. 20 Phase difference measurement result S 50 From the calibration signal S 20 The frequency characteristic of the second calibration signal S is obtained. Next, the switches SW10, SW1, and SW21 to SW24 are set to the lower side in the figure, and the switches SW3 and SW4 are set to the upper side in the figure. 21 is input to the millimeter wave band signal measuring unit 70 and the frequency converted output signal S 70 Phase difference measurement result S 50' to output signal S 70 The frequency characteristic of the calibration signal S 20 and the frequency characteristic of the output signal S of the millimeter wave band signal measuring unit 70 70 The frequency characteristics of the downconverter (frequency conversion units 72, 73) of the millimeter wave band signal measuring unit 70 are obtained from the frequency characteristics of the downconverter and the phase correction value calculating unit 55. The phase correction value calculating unit 55 calculates the frequency characteristics of the downconverter over a predetermined frequency range and outputs them to the phase correction unit 74 of the millimeter wave band signal measuring unit 70.

[0037] The measured signal S transmitted from the millimeter wave band signal transmitting unit 60 60 When measuring, the switches SW3 and SW4 are set to the lower side in FIG. 28. The millimeter wave band signal transmitting section 60 up-converts an intermediate frequency signal generated by an intermediate frequency signal generating section 61 by a local signal generating section 62 and a frequency converting section 63 to generate a signal to be measured S 60 The measured signal S 60 is input to the millimeter wave band signal measuring unit 70 via the switch SW3, and is down-converted by the frequency conversion unit 72 and the intermediate frequency signal conversion unit 73 to produce an output signal S 70' is input to the phase correction unit 74. The phase correction unit 74 divides it by the frequency characteristic of the downconverter of the millimeter waveband signal measuring unit 70 (if only the phase is to be corrected, the phase characteristic of the frequency conversion units 72, 73 of the millimeter waveband signal measuring unit 70 is subtracted), thereby obtaining a measurement result in which the frequency characteristics of the frequency conversion units 72, 73 of the millimeter waveband signal measuring unit 70 have been corrected.

[0038] <Third configuration example> 29 shows a third configuration example of a conventional phase characteristic calibration device. The conventional phase characteristic calibration device 1000C calibrates the phase characteristic of an up-converter (frequency conversion unit 84) of a millimeter wave band signal generating unit 80 by using a three-tone signal as a calibration signal. For this purpose, the phase characteristic calibration device 1000C includes a short pulse light source 2, an optical branching unit 3, an optical variable delay unit 4, a three-tone intermediate frequency signal generating unit 10, a reference signal modulation unit 17, a synchronization processing unit 5, an electro-optic sampling unit 30, a lock-in detection unit 40, a three-tone phase difference measurement unit 50, and a phase correction value calculation unit 55. The phase characteristic calibration apparatus 1000C according to the third configuration example differs from the first configuration example (FIG. 27) in which the phase characteristic of the downconverter of the millimeter wave band signal measuring unit 70 is calibrated, in that the calibration signal generating unit 20 of the first configuration example (FIG. 27) has only a three-tone intermediate frequency signal generating unit 10 and a reference signal modulating unit 17, and in that the phase characteristic of the upconverter of the millimeter wave band signal generating unit 80 is calibrated. The other configurations are the same as those of the first configuration example, and the same configurations are denoted by the same reference symbols, and detailed descriptions thereof will be omitted as appropriate.

[0039] The millimeter wave band signal generating section 80 includes an intermediate frequency signal generating section 81, a phase correcting section 82, a local signal generating section 83, and a frequency converting section 84. The intermediate frequency signal generating section 81 generates an intermediate frequency signal S 81 and sends it to the phase correction unit 82. The phase correction unit 82 generates the intermediate frequency signal S 81 When the switches SW6 and SW7 are set to the lower position in the figure, the frequency converter 84 converts the local oscillator signal S generated by the local oscillator signal generator 83 into a phase-corrected intermediate frequency signal, as described below, and outputs the phase-corrected intermediate frequency signal. 83 The phase-corrected intermediate frequency signal is up-converted to produce a millimeter-wave measurement signal S 80' Generate the measurement signal S 80' is sent to the millimeter waveband signal receiving unit 90 via the switch SW7.

[0040] The millimeter wave band signal receiving unit 90 includes a local signal generating unit 91, a frequency converting unit 92, and an intermediate frequency signal converting unit 93. The millimeter wave band measurement signal S 80' The frequency converter 92 converts the local oscillator signal S 91 The signal is down-converted by the intermediate frequency signal converter 93, which performs processing such as frequency conversion to generate an intermediate frequency signal S 90 will be output as:

[0041] The calibration method is as follows. First, set the switches SW6 and SW7 to the upper side in the figure. 10 Let S be the reference signal. 18 and modulating the modulated three-tone intermediate frequency signal S 19 is input to the frequency converter 84 of the millimeter wave band signal generator 80 to produce a frequency-converted millimeter wave band signal S 80 Phase difference measurement result S 50 From millimeter wave signal S 80 This becomes the frequency characteristic of the up-converter (frequency conversion unit 84) of the millimeter wave band signal generating unit 80. The phase correction value calculating unit 55 calculates the frequency characteristic of the up-converter over a predetermined frequency range, and outputs it to the phase correcting unit 82 of the millimeter wave band signal generating unit 80.

[0042] The measurement signal S transmitted from the millimeter wave band signal generating unit 80 80' When the millimeter wave band signal receiving unit 90 receives the intermediate frequency signal S output from the intermediate frequency signal generating unit 81, the switches SW6 and SW7 are set to the lower side in FIG. 81 The intermediate frequency signal having its phase corrected by the phase corrector 82 is converted into a local oscillator signal S from a local oscillator signal generator 83 by a frequency converter 84. 83 and the millimeter-wave measurement signal S 80' The millimeter wave band signal receiving unit 90 outputs the measurement signal S 80' The local oscillator signal S from the local oscillator signal generator 91 is received by the frequency converter 92. 91 The signal is down-converted by the intermediate frequency signal converter 93, and frequency conversion is performed to generate an intermediate frequency signal S 90 In this way, the measurement signal S , whose frequency characteristics have been corrected by the frequency conversion section 84, is output. 80' The result received by the millimeter waveband signal receiving unit 90, which is the measurement target, can be obtained.

[0043] <Fourth configuration example> 30 shows a fourth configuration example of a conventional phase characteristic calibration device. The conventional phase characteristic calibration device 1000D calibrates the phase characteristic of an up-converter (frequency conversion unit 84) of a millimeter wave band signal generating unit 80 by using a four-tone signal as a calibration signal. For this purpose, the phase characteristic calibration device 1000D includes a short pulse light source 2, an optical branching unit 3, an optical variable delay unit 4, a multi-tone intermediate frequency signal generating / reference signal modulating unit 10B, a synchronization processing unit 5, an electro-optic sampling unit 30, a multi-tone signal separating unit 40B, a multi-tone phase difference measuring unit 50B, and a phase correction value calculating unit 55. The phase characteristic calibration apparatus 1000D according to the fourth configuration example differs from the second configuration example in that the calibration signal generating section 20B of the second configuration example (FIG. 28) has only a multi-tone intermediate frequency signal generating / reference signal modulating section 10B and in that the phase characteristic of the up-converter of the millimeter wave band signal generating section 80 is calibrated, and the other configurations are the same as those of the second configuration example. The millimeter wave band signal generating section 80 and the millimeter wave band signal receiving section 90 are the same as those shown in the third configuration example (FIG. 29). The same components are denoted by the same reference numerals, and detailed description will be omitted as appropriate.

[0044] In the fourth configuration example, when the switches SW6 and SW7 are set to the upper side in the figure, the multi-tone intermediate frequency signal S output from the multi-tone intermediate frequency signal generating / reference signal modulating unit 10B is 10 is up-converted by the frequency conversion unit 84 of the millimeter wave band signal generating unit 80 to produce a millimeter wave band signal S 80 The millimeter wave signal S 80 is input to electro-optic sampling section 30, passes through multi-tone signal separation section 40B, and the phase difference is calculated in multi-tone phase difference measurement section 50B.

[0045] The calibration method is as follows. First, set the switches SW6 and SW7 to the upper side in FIG. 80 is input to the electro-optic sampling unit 30 and measured. 80 Phase difference measurement result S 50The frequency characteristics of the frequency conversion unit 84 of the millimeter wave band signal generating unit 80 are obtained from the above. The phase correction value calculating unit 55 calculates the frequency characteristics of the frequency conversion unit 84 over a predetermined frequency range and outputs the calculated frequency characteristics to the phase correction unit 82 of the millimeter wave band signal generating unit 80.

[0046] The measurement signal S transmitted from the millimeter wave band signal generating unit 80 80' When the millimeter wave band signal receiving unit 90 receives the intermediate frequency signal S 1 , the switches SW6 and SW7 are set to the lower side in FIG. 81 is input to a phase correction unit 82 for phase correction, and is up-converted by a local signal generation unit 83 and a frequency conversion unit 84 to generate a millimeter wave band measurement signal S 80' is generated and input to the millimeter waveband signal receiving unit 90, thereby obtaining a measurement signal S in which the frequency characteristics of the frequency conversion unit 84 have been corrected. 80' The result received by the millimeter waveband signal receiving unit 90, which is the measurement target, can be obtained. In all configuration examples, in Figures 27 to 30, the optical variable delay device 4 is placed between the optical branching device 3 and the electro-optical sampling unit 30, but since it is only necessary to change the relative time difference between the short pulse light input to the electro-optical sampling unit and the calibration signal / millimeter waveband signal, it is also possible to place the optical variable delay device 4 between the optical branching device 3 and the synchronization processing unit 5. [Prior art documents] [Patent documents]

[0047] [Patent Document 1] JP 2020-193848 A Summary of the Invention [Problem to be solved by the invention]

[0048] In the conventional technology, an electro-optic sampling method is used to sweep an optical variable delay at a constant sweep speed, thereby electro-optically sampling the time waveform of a millimeter-wave tone signal (calibration signal) at constant time intervals. However, in the actual sweep of an optical variable delay, unpredictable random fluctuations in the sweep speed, such as mechanical rattles, can occur. If the sweep speed of the optical variable delay is not constant, the time intervals of the electro-optic sampling are not constant, causing the phase of the electro-optically sampled tone signal to fluctuate and the signal-to-noise ratio to decrease, resulting in a problem of deteriorating accuracy of phase characteristic calibration.

[0049] Regarding this problem, the present inventor has proposed a method of forming an interferometer using an optical path where the output of a CW laser passes through an optical variable delay device and an optical path where the output does not pass through, and correcting the delay amount based on an interference signal obtained by the interference light generated by the interferometer (Patent Application No. 2023-039791). Specifically, an interferometer is formed using an optical path where the output of a CW laser passes through an optical variable delay device and an optical path where the output does not pass through, and when the optical variable delay device is swept at an almost constant speed and the output of the interferometer is input to a photoreceiver, a sine wave with an almost constant period is obtained as an interference signal. The peak of this interference signal waveform is observed when the optical path length difference becomes an integer multiple of the CW light wavelength. The interference signal is divided by an appropriate frequency divider, and a signal obtained by electro-optically sampling a millimeter-wave tone signal (calibration signal) is A / D converted as a clock signal for the A / D converter. The CW light and the short pulse light may be separated using a polarizing beam splitter (PBS) or a wavelength filter.

[0050] <Fifth Configuration Example> More specifically, the configuration is as shown in FIG. The phase characteristic calibration device 1000E corrects the phase frequency characteristics of the down converter (frequency conversion unit 72, intermediate frequency signal conversion unit 73) of the millimeter wave band signal measurement unit 70 that measures the signal under test by frequency converting (down converting) the signal under test. For this purpose, the phase characteristic calibration device 1000E includes a short pulse light source 2, an optical branching unit 3, an optical variable delay unit 4, a calibration signal generation unit 20, a synchronization processing unit 5, an electro-optic sampling unit 30, a lock-in detection unit 40, a multi-tone phase difference measurement unit 50, a phase correction value calculation unit 55, and a delay amount correction unit 100 for correcting the amount of delay caused by the optical variable delay unit 4. The short pulse light source 2, the optical branching unit 3, the optical variable delay unit 4, the calibration signal generating unit 20, the synchronization processing unit 5, the electro-optic sampling unit 30, the lock-in detection unit 40, the multi-tone phase difference measuring unit 50, and the phase correction value calculating unit 55 have the same configuration as those in the conventional technology shown in FIG. 27, and therefore the same reference numerals are used and the description thereof will be omitted. Next, the delay amount correcting section 100 will be described.

[0051] The delay amount correction unit 100 corrects phase fluctuations in the multi-tone signal obtained by electro-optic sampling, which are caused by instability in the sweep speed of the optical variable delay unit 4, and as shown in FIG. 31, includes a CW light source 101, an interferometer 110, a photoreceiver 106, a frequency divider 107, and a multi-tone signal sampling unit 120.

[0052] The CW light source 101 is, for example, a semiconductor laser, and is adapted to generate CW light of a predetermined wavelength.

[0053] The interferometer 110 is configured such that CW light is input to a first optical path including an optical variable delay device 4 and a second optical path not including an optical variable delay device 4, and causes the CW light output from the first optical path and the CW light output from the second optical path to interfere with each other, and outputs the interfered light.

[0054] Specifically, the interferometer 110 includes an optical splitter 102, an optical multiplexer 103 such as a half mirror, an optical splitter 104 such as a half mirror, and an optical multiplexer 105. The optical splitter 102 is provided at a branch point between the first optical path and the second optical path, and splits the CW light output from the CW light source 101 into a first CW light and a second CW light. The optical multiplexer 103 is provided in the first optical path, and receives the first CW light and the short pulse light sent from the short pulse light source 2 via the optical splitter 3, and multiplexes the first CW light and the short pulse light to output to the first optical path. The optical demultiplexer 104 is provided on the first optical path on the opposite side to the optical multiplexer 103 with the optical variable delay device 4 interposed therebetween, and outputs the first CW light and short pulse light that have passed through the optical variable delay device 4 on the first optical path to the electro-optic sampling unit 30 and the optical multiplexer 105. The optical multiplexer 105 is provided at the joining point of the first optical path and the second optical path, and generates interference light by multiplexing the first CW light and short pulse light output by the optical demultiplexer 104 with the second CW light that has been separated by the optical demultiplexer 102. In other words, the first CW light that has passed through the optical variable delay device 4 interferes with the second CW light sent from the optical demultiplexer 102 side.

[0055] The optical receiver 106 includes, for example, a low-speed photodiode, detects the intensity of the interference light generated by the optical multiplexer 105, and outputs it as an interference signal. The interference signal is a sinusoidal repetitive signal that reaches a peak when the optical path length difference (delay time) between the first optical path and the second optical path is equal to an integer multiple of the wavelength (period) of the CW light.

[0056] The frequency divider 107 divides the frequency of the interference signal output from the photoreceiver 106. If the division ratio of the frequency divider 107 is N (N is an integer), then a rectangular wave in which the optical path length difference (delay time) between the first optical path and the second optical path rises every N times the wavelength (period) of the CW light is output from the frequency divider 107.

[0057] Multi-tone signal sampling section 120 samples the multi-tone signal output from lock-in detection section 40 in accordance with the output of frequency divider 107, and outputs the sampled multi-tone signal as a corrected multi-tone signal. Specifically, multi-tone signal sampling section 120 includes an A / D converter 111 that performs A / D conversion on the multi-tone signal detected by lock-in detection section 40, and the output signal of frequency divider 107 is used as an A / D conversion clock signal for A / D converter 111. For example, A / D converter 111 A / D converts the multi-tone signal at the rising edge of the output signal of frequency divider 107.

[0058] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at constant intervals relative to the delay amount, regardless of the sweep speed of the variable optical delay device 4. If a CW laser or the like with a relatively stable wavelength is used as the CW light source 101, the phase fluctuation of the multi-tone signal obtained by electro-optic sampling, which is caused by the instability of the sweep speed of the variable optical delay device 4, can be corrected.

[0059] <Sixth Configuration Example> FIG. 32 shows another configuration of the prior art. Calibration signal generating unit 20B, multi-tone signal separating unit 40B, and multi-tone phase difference measuring unit 50B are the same as those denoted by the same reference characters in Fig. 28, and therefore their descriptions will be omitted. The short pulse light source 2, optical branching unit 3, optical variable delay unit 4, synchronization processing unit 5, electro-optic sampling unit 30, phase correction value calculating unit 55, and delay amount correcting unit 100 are the same as those denoted by the same reference characters in Fig. 31, and therefore their descriptions will be omitted. Multi-tone signal sampling unit 120B samples each tone signal output from multi-tone signal separating unit 40B in accordance with the output of frequency divider 107, and outputs the signals as four corrected tone signals.

[0060] With this configuration, each tone signal obtained by electro-optic sampling is sampled at a constant interval with respect to the delay amount, regardless of the sweep speed of the variable optical delay device 4. If a CW laser or the like with a relatively stable wavelength is used as the CW light source 101, phase fluctuation of each tone signal obtained by electro-optic sampling, which is caused by instability in the sweep speed of the variable optical delay device 4, can be corrected. Furthermore, it has both the function of lock-in detection and the function of separating multi-tone signals, and can achieve the same effect as in FIG.

[0061] <Seventh Configuration Example> FIG. 33 shows another conventional configuration for calibrating the phase characteristic of the millimeter waveband signal generating section 80. In FIG. The three-tone intermediate frequency signal generating section 10, reference signal modulating section 17, lock-in detecting section 40, multi-tone signal sampling section 120, short pulse light source 2, optical splitter 3, variable optical delay section 4, synchronization processing section 5, electro-optic sampling section 30, three-tone phase difference measuring section 50, phase correction value calculating section 55 and delay amount correcting section 100 have the same reference numerals as in Fig. 31 and will not be described. The millimeter waveband signal generating section 80 and millimeter wave signal receiving section 90 are the same as in Fig. 29, and the phase characteristic calibrating method for the millimeter waveband signal generating section 80 is also the same.

[0062] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at constant intervals relative to the delay amount, regardless of the sweep speed of the variable optical delay device 4. If a CW laser or the like with a relatively stable wavelength is used as the CW light source 101, the phase fluctuation of the multi-tone signal obtained by electro-optic sampling, which is caused by the instability of the sweep speed of the variable optical delay device 4, can be corrected.

[0063] <8th Configuration Example> FIG. 34 shows another conventional configuration for calibrating the phase characteristic of the millimeter waveband signal generating section 80. In FIG. The multi-tone intermediate frequency signal generating / reference signal modulating section 10B, multi-tone signal separating section 40B, multi-tone signal sampling section 120B, multi-tone phase difference measuring section 50B, short pulse light source 2, optical branching section 3, optical variable delay section 4, synchronization processing section 5, electro-optic sampling section 30, phase correction value calculating section 55 and delay amount correcting section 100 are the same as those in Fig. 32 with the same reference numerals assigned thereto, and therefore their explanation will be omitted. The millimeter waveband signal generating section 80 and millimeter wave signal receiving section 90 are the same as those in Fig. 30, and the phase characteristic calibrating method for the millimeter waveband signal generating section 80 is also the same.

[0064] With this configuration, each tone signal obtained by electro-optic sampling is sampled at a constant interval with respect to the delay amount, regardless of the sweep speed of the variable optical delay device 4. If a CW laser or the like with a relatively stable wavelength is used as the CW light source 101, phase fluctuation of each tone signal obtained by electro-optic sampling, which is caused by instability in the sweep speed of the variable optical delay device 4, can be corrected. Furthermore, it has both the function of lock-in detection and the function of separating multi-tone signals, and can achieve the same effect as in FIG.

[0065] In the configurations shown in Figures 27 to 30, the electro-optic sampling method electro-optically samples the time waveform of the millimeter-wave tone signal (calibration signal) by scanning the optical variable delay device 4 at a constant sweep speed. However, the sweep speed of an actual optical variable delay device is not constant, and the phase of the electro-optically sampled tone signal fluctuates, resulting in a decrease in the signal-to-noise ratio. Therefore, as shown in Figures 31 to 34, an invention has been proposed in which an interferometer 110 is configured using an optical path in which the output of a CW light source 101 passes through the optical variable delay device 4 and an optical path in which it does not pass through (Patent Application No. 2023-039791).

[0066] However, in the conventional configurations (configuration examples 5 to 8) shown in Figures 31 to 34, the optical system becomes complicated due to the use of a CW laser, and a polarizing beam splitter or wavelength filter is required to separate the CW light and the short pulse light, and there were issues that needed to be improved from the standpoint of cost-effectiveness in selecting optical components.

[0067] The present invention has been made to solve the above-mentioned problems, and has an object to provide a phase characteristic calibration device and a phase characteristic calibration method that do not require a CW light source in an interferometer and are highly cost-effective. [Means for solving the problem]

[0068] In order to achieve the above object, the phase characteristic calibration device according to the present invention includes a pulse light source (2) that generates pulse light of a predetermined repetition frequency, an optical branching unit (3) that branches the pulse light, a multi-tone intermediate frequency signal generating unit (10, 17) that combines three or more intermediate frequency signals having different frequencies and outputs a multi-tone intermediate frequency signal modulated by a reference signal, a calibration signal generating unit (20) that generates a calibration signal by up-converting the multi-tone intermediate frequency signal using a local signal of a predetermined frequency and a frequency converting unit (21), a synchronization processing unit (5) to which one of the pulse lights output from the optical branching unit is input and that controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulse light, an electro-optic sampling unit (30) to which the other of the pulse light output from the optical branching unit is input and that samples the calibration signal in accordance with the pulse light and outputs it as an electrical signal, and a variable delay (4) receiving one or the other of the pulsed lights and changing a relative time difference between the pulsed light and the calibration signal input to the electro-optic sampling unit; a lock-in detection unit (40) acquiring the electrical signal while changing the relative time difference and modulating the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the three or more intermediate frequency signals included in the electrical signal; an interferometer (110) receiving CW light input to a first optical path including the variable delay and a second optical path not including the variable delay, multiplexing the CW light output from the first optical path and the CW light output from the second optical path to cause interference and outputting the interference light; a photoreceiver (106) detecting the intensity of the interference light; a frequency divider (107) dividing the frequency of the interference signal output from the photoreceiver; and a multi-tone signal sampling unit (120) sampling the multi-tone signal output from the lock-in detection unit according to an output of the frequency divider and outputting the multi-tone signal as a corrected multi-tone signal;a multi-tone phase difference measurement unit (50) that detects a phase difference between three or more tone signals corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal, and a phase correction value calculation unit (55) that calculates a phase correction value for correcting the phase-frequency characteristic of a down-converter (72, 73) of a signal measurement unit (70) from the phase difference between the tone signals, wherein the phase characteristic calibration device (1; 1A) calibrates the phase-frequency characteristic of the down-converter of the signal measurement unit that down-converts and measures a signal under measurement, wherein the pulsed light input to the variable delay unit is used instead of the CW light, and the interferometer includes an optical bandpass filter (108) that expands the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

[0069] As described above, the phase characteristic calibration device according to the present invention is provided with an optical bandpass filter (hereinafter also referred to as an optical BPF) to expand the pulse width of at least one of the pulse light output from the first optical path and the pulse light output from the second optical path so that the light input to the optical receiver interferes. An interference signal can be obtained by inputting the interference light in which the mode of the pulse light is limited by the optical BPF to the optical receiver. Expanding the pulse width by providing an optical bandpass filter so that the pulse light of the first optical path and the pulse light of the second optical path interfere with each other means transmitting only a part of the mode of the pulse light on the frequency axis. One of the modes constituting the pulse light corresponds to CW light. This eliminates the need for a CW light source in the interferometer, and improves the complexity and cost-effectiveness of the optical system compared to the conventional technology (fifth configuration example) shown in FIG. 31. Pulsed light is a collection of many spectral lines spaced apart by the repetition frequency. In this specification, a mode refers to one of these spectral lines.

[0070] Also, it is possible to correct phase fluctuations in the multi-tone signal resulting from instability in the sweep speed of the variable delay element, as in the fifth configuration example shown in Fig. 31. Since phase fluctuations in the corrected multi-tone signal obtained by the multi-tone signal sampling unit are reduced, the S / N ratio is improved, thereby making it possible to improve the accuracy of phase characteristic calibration.

[0071] The phase characteristic calibration device according to the present invention includes a pulse light source (2) that generates pulse light of a predetermined repetition frequency, an optical branching unit (3) that branches the pulse light, and a multi-tone intermediate frequency signal generating unit (10B) that outputs a multi-tone intermediate frequency signal obtained by modulating and combining three or more intermediate frequency signals having different frequencies with the same number of mutually orthogonal reference signals as the intermediate frequency signals, the calibration signal generating unit (20B) up-converting the multi-tone intermediate frequency signal using a local signal of a predetermined frequency and a frequency conversion unit (21) to generate a calibration signal, a synchronization processing unit (5) to which one of the pulse lights output from the optical branching unit is input and which controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulse light, an electro-optic sampling unit (30) to which the other of the pulse lights output from the optical branching unit is input and which samples the calibration signal in accordance with the pulse light and outputs it as an electrical signal, and a variable delay unit (4) for receiving one or the other of the pulsed lights and changing the relative time difference between the pulsed lights and the calibration signal input to the electro-optic sampling unit; a multi-tone signal separation unit (40B) for acquiring the electrical signal while changing the relative time difference and modulating the electrical signal with sine waves having the same frequency as each of the reference signals and being orthogonal to each other, thereby separating tone signals corresponding to the three or more intermediate frequency signals contained in the electrical signal; an interferometer (110) that multiplexes the CW light output from the first optical path and the CW light output from the second optical path to cause interference and output the interference light; a photoreceiver (106) that detects the intensity of the interference light; a frequency divider (107) that divides the frequency of the interference signal output from the photoreceiver; and a multi-tone signal sampling unit (120B) that samples each of the tone signals output from the multi-tone signal separation unit in accordance with the output of the frequency divider and outputs the sampled tone signals as corrected tone signals;a multi-tone phase difference measurement unit (50B) detecting a phase difference between the corrected tone signals, and a phase correction value calculation unit (55) calculating a phase correction value for correcting the phase-frequency characteristic of a down-converter (72, 73) of a signal measurement unit (70) from the phase difference between the corrected tone signals, wherein the phase characteristic calibration device (1B; 1C) calibrates the phase-frequency characteristic of the down-converter of the signal measurement unit that down-converts and measures a signal under measurement, wherein the pulsed light input to the variable delay unit is used instead of the CW light, and the interferometer includes an optical bandpass filter (108) that expands the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

[0072] As described above, the phase characteristic calibration device according to the present invention is provided with an optical bandpass filter to expand the pulse width of at least one of the pulse light output from the first optical path and the pulse light output from the second optical path so that the light input to the optical receiver interferes. An interference signal can be obtained by inputting the interference light in which the mode of the pulse light is limited by the optical bandpass filter to the optical receiver. Expanding the pulse width by providing an optical bandpass filter so that the pulse light of the first optical path and the pulse light of the second optical path interfere with each other means transmitting only a part of the mode of the pulse light on the frequency axis. One of the modes constituting the pulse light corresponds to CW light. This eliminates the need for a CW light source in the interferometer, and improves the complexity and cost-effectiveness of the optical system compared to the conventional technology (sixth configuration example) shown in FIG. 32.

[0073] 32, each tone signal output from the multi-tone signal separation unit is sampled according to the output of a frequency divider that divides the frequency of the interference signal, so that each tone signal obtained by electro-optic sampling is sampled at regular intervals with respect to the delay amount itself, regardless of the sweep speed of the variable delay unit. Since the phase fluctuation of the corrected multi-tone signal obtained by the multi-tone signal sampling unit is reduced, the S / N ratio is improved, and the accuracy of phase characteristic calibration can be improved.

[0074] Also, as in Fig. 28, each tone signal is separated in the multi-tone signal separator placed before the multi-tone phase difference measurement unit, so it is possible to arrange each tone signal at a frequency interval narrower than the frequency resolution Δf=1 / T determined by the sweep width T of the variable delay device, and the frequency interval can be narrowed without increasing the size of the variable delay device. In other words, phase measurement is possible with high frequency resolution regardless of the sweep width of the variable delay device.

[0075] In order to achieve the above object, the phase characteristic calibration device according to the present invention includes a pulse light source (2) that generates pulse light of a predetermined repetition frequency, an optical branching unit (3) that branches the pulse light, and a multi-tone intermediate frequency signal generating unit (10, 17) that combines three or more intermediate frequency signals having different frequencies and outputs a multi-tone intermediate frequency signal modulated by a reference signal, wherein a signal generating unit (80) that up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, a synchronization processing unit (5) that receives one of the pulse lights outputted from the optical branching unit and controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulse light, and an electro-optic sampling unit (6) that receives the other of the pulse lights outputted from the optical branching unit and samples the calibration signal in accordance with the pulse light to output it as an electrical signal. a variable delay (4) to which one or the other of the pulsed lights output from the optical splitter is input and which changes the relative time difference between the pulsed light input to the electro-optic sampling unit and the calibration signal; a lock-in detection unit (40) which acquires the electrical signal while changing the relative time difference and modulates the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the three or more intermediate frequency signals contained in the electrical signal; an interferometer (110) that multiplexes and interferes with the CW light output from the first optical path and the CW light output from the second optical path and outputs the interference light; a photoreceiver (106) that detects the intensity of the interference light; a frequency divider (107) that divides the frequency of the interference signal output from the photoreceiver; and a multi-tone signal sampling unit (120) that samples the multi-tone signal output from the lock-in detection unit in accordance with the output of the frequency divider and outputs the multi-tone signal as a corrected multi-tone signal;a multi-tone phase difference measurement unit (50) that detects a phase difference between three or more tone signals corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal, and a phase correction value calculation unit (55) that calculates a phase correction value for correcting the phase frequency characteristic of the up-converter of the signal generating unit from the phase difference between the tone signals, the pulsed light input to the variable delay unit is used instead of the CW light, and the interferometer includes an optical bandpass filter (108) that expands the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

[0076] As described above, the phase characteristic calibration device according to the present invention is provided with an optical bandpass filter to expand the pulse width of at least one of the pulse light output from the first optical path and the pulse light output from the second optical path so that the light input to the optical receiver interferes. An interference signal can be obtained by inputting the interference light in which the mode of the pulse light is limited by the optical bandpass filter to the optical receiver. Expanding the pulse width by providing an optical bandpass filter so that the pulse light of the first optical path and the pulse light of the second optical path interfere with each other means transmitting only a part of the mode of the pulse light on the frequency axis. One of the modes constituting the pulse light corresponds to CW light. This eliminates the need for a CW light source in the interferometer, and improves the complexity and cost-effectiveness of the optical system compared to the conventional technology (seventh configuration example) shown in FIG. 33.

[0077] Also, as in FIG. 33, when correcting the phase-frequency characteristic of the up-converter of the signal generating section which up-converts the measurement intermediate frequency signal and outputs it as a measurement signal, it is possible to reduce phase fluctuation of the multi-tone signal caused by instability in the sweep speed of the variable delay device, etc., and improve the S / N ratio.

[0078] In order to achieve the above object, the phase characteristic calibration device according to the present invention includes a pulse light source (2) that generates pulse light of a predetermined repetition frequency, an optical branching device (3) that branches the pulse light, and a multi-tone intermediate frequency signal generating unit (10B) that outputs a multi-tone intermediate frequency signal obtained by modulating and combining three or more intermediate frequency signals having different frequencies with the same number of mutually orthogonal reference signals as the intermediate frequency signals, and a signal generating unit (80) that up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, and generates the multi-tone intermediate frequency signal by using a local oscillator signal of a predetermined frequency. a synchronization processing unit (5) which receives one of the pulsed lights output from the optical splitter and controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the upconverted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulsed light; and an electro-optical sampling unit (6) which receives the other of the pulsed lights output from the optical splitter and samples the calibration signal in accordance with the pulsed light to output it as an electrical signal. a variable delay unit (4) to which one or the other of the pulsed lights output from the optical splitter is input and which changes the relative time difference between the pulsed light input to the electro-optic sampling unit and the calibration signal; a multi-tone signal separation unit (40B) which acquires the electrical signal while changing the relative time difference and modulates the electrical signal with sine waves having the same frequency as each of the reference signals and which are orthogonal to each other, thereby separating tone signals corresponding to the three or more intermediate frequency signals contained in the electrical signal; an interferometer (110) that multiplexes the CW light output from the first optical path and the CW light output from the second optical path, causes interference between the CW light and outputs the interference light; a photoreceiver (106) that detects the intensity of the interference light; a frequency divider (107) that divides the frequency of the interference signal output from the photoreceiver; and a multi-tone signal sampling unit (120B) that samples each of the tone signals output from the multi-tone signal separation unit in accordance with the output of the frequency divider, and outputs the sampled tone signals as corrected tone signals;a multi-tone phase difference measurement unit (50B) that detects a phase difference between the corrected tone signals, and a phase correction value calculation unit (55) that calculates a phase correction value for correcting the phase frequency characteristic of the up-converter of the signal generating unit from the phase difference between the corrected tone signals, the pulsed light input to the variable delay unit is used instead of the CW light, and the interferometer includes an optical bandpass filter (108) that expands the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

[0079] As described above, the phase characteristic calibration device according to the present invention is provided with an optical bandpass filter to expand the pulse width of at least one of the pulse light output from the first optical path and the pulse light output from the second optical path so that the light input to the optical receiver interferes. An interference signal can be obtained by inputting the interference light in which the mode of the pulse light is limited by the optical bandpass filter to the optical receiver. Expanding the pulse width by providing an optical bandpass filter so that the pulse light of the first optical path and the pulse light of the second optical path interfere with each other means transmitting only a part of the mode of the pulse light on the frequency axis. One of the modes constituting the pulse light corresponds to CW light. This eliminates the need for a CW light source in the interferometer, and improves the complexity and cost-effectiveness of the optical system compared to the conventional technology (eighth configuration example) shown in FIG. 34.

[0080] Also, as in FIG. 34, when correcting the phase-frequency characteristic of the up-converter of the signal generating section which up-converts the measurement intermediate frequency signal and outputs it as a measurement signal, the accuracy of phase characteristic calibration can be improved by reducing the phase fluctuation of each tone signal caused by instability in the sweep speed of the variable delay device, etc., and improving the S / N ratio.

[0081] 30, each tone signal is separated in the multi-tone signal separator placed before the multi-tone phase difference measurement unit, so it is possible to arrange each tone signal at a frequency interval narrower than the frequency resolution Δf=1 / T determined by the sweep width T of the variable delay device, and the frequency interval can be narrowed without increasing the size of the variable delay device. In other words, phase measurement is possible with high frequency resolution regardless of the sweep width of the variable delay device.

[0082] In the phase characteristic calibration device according to the present invention, the optical bandpass filter may be provided in at least one of the first optical path and the second optical path, or between a multiplexing section that multiplexes the pulsed light output from the first optical path and the pulsed light output from the second optical path, and the optical receiver.

[0083] As described above, the phase characteristic calibration device according to the present invention has an optical BPF in at least one of the first optical path and the second optical path. This expands the pulse width of at least one of the pulse light output from the first optical path and the pulse light output from the second optical path. Alternatively, an optical BPF is provided between the multiplexing section and the optical receiver. This expands the pulse width of both the pulse light output from the first optical path and the pulse light output from the second optical path. An interference signal can be obtained by inputting interference light in which the mode of the pulse light is limited by the optical BPF to the optical receiver. This eliminates the need for a CW light source in the interferometer, and improves the complexity and cost-effectiveness of the optical system compared to the conventional techniques (configuration examples 5 to 8) shown in Figs. 31 to 34.

[0084] In the phase characteristic calibration device according to the present invention, the optical bandpass filter may be configured to limit the spectral width of the pulsed light and pass a plurality of line spectral components of the pulsed light.

[0085] As described above, in the phase characteristic calibration device according to the present invention, the optical BPF provided for interfering the pulsed light in the first optical path and the pulsed light in the second optical path passes a plurality of line spectrum components, so the passband of the optical BPF may be approximately the same as or larger than the repetition frequency of the pulsed light. Therefore, the finesse required for the optical BPF is not high compared to the case where the optical BPF passes only one line spectrum of the pulsed light. Therefore, the optical BPF can be realized relatively easily.

[0086] In the phase characteristic calibration device according to the present invention, the optical bandpass filter may include a first etalon (108a) having a free spectral range (FSR) narrower than the spectral width of the pulsed light, and a second etalon (108b) having a free spectral range (FSR) narrower than the spectral width of the pulsed light and having a free spectral range (FSR) different from that of the first etalon.

[0087] As described above, by combining two etalons with different FSRs (i.e., cavity lengths), the least common multiple of the two FSRs becomes the FSR of the combined etalons (i.e., the optical BPF), which can be made larger than the FSR of a single etalon. Since the FSR of each etalon can be made narrower than the spectral width of the pulsed light, the finesse of each etalon does not need to be high, and the optical BPF can be realized relatively easily. Here, the spectral width of the pulsed light does not mean the width of a single line spectrum, but the width of the envelope of the entire spectrum consisting of multiple line spectra of the pulsed light. This eliminates the need for a CW light source in the interferometer, improving the complexity and cost-effectiveness of the optical system compared to conventional techniques.

[0088] In the phase characteristic calibration device according to the present invention, the optical bandpass filter may include an etalon (108c) whose free spectral range (FSR) is narrower than the spectral width of the pulsed light, and a wavelength filter (108d) whose passband is narrower than twice the free spectral range (FSR) of the etalon.

[0089] For example, a wavelength filter with a passband width of several tens of GHz can be made using products that use Bragg reflectors or diffraction gratings. An etalon with an FSR equivalent to the passband width of the wavelength filter can be used, and the finesse of the etalon does not need to be high, so an optical BPF can be easily realized. This eliminates the need for a CW light source in the interferometer, improving the complexity and cost-effectiveness of the optical system compared to conventional technologies.

[0090] In the phase characteristic calibration device according to the present invention, the interferometer includes a first optical splitter (103) that is provided at a branching point between the first optical path and the second optical path, splits the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputs the first pulsed light toward the first optical path, and outputs the second pulsed light toward the second optical path; and a second optical splitter (104) that is provided on the opposite side of the first optical splitter across the variable delay device in the first optical path, receives as input the first pulsed light that has passed through the variable delay device, splits the input first pulsed light into a third pulsed light and a fourth pulsed light, and outputs the third pulsed light toward the first optical path. the optical multiplexer (105) provided at a joining portion of the first optical path and the second optical path, the optical multiplexer configured to multiplex the second pulsed light separated by the first optical multiplexer and the third pulsed light separated by the second optical multiplexer to generate a fifth pulsed light; and the optical bandpass filter provided between the optical multiplexer and the photodetector, the optical bandpass filter receiving the fifth pulsed light and generating the interference light, wherein the optical bandpass filter expands the pulse width of both the pulsed light output from the first optical path and the pulsed light output from the second optical path.

[0091] With this configuration, the phase characteristic calibration device according to the present invention has an optical BPF between the optical multiplexer and the optical receiver. This expands the pulse width of both the pulse light output from the first optical path and the pulse light output from the second optical path. Since the optical BPF is provided to restrict the mode of the pulse light so that the light input to the optical receiver interferes, a CW light source is not required for the interferometer light, and the complexity and cost-effectiveness of the optical system are improved compared to the conventional technology.

[0092] In the phase characteristic calibration device according to the present invention, the interferometer includes a first optical splitter (103) provided at a branching point of the first optical path and the second optical path, splitting the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputting the first pulsed light toward the first optical path, and outputting the second pulsed light toward the second optical path; and an optical bandpass filter that is provided between the optical multiplexer / demultiplexer and the photodetector and receives the third pulsed light and generates the interference light, wherein the optical bandpass filter expands the pulse width of both the pulsed light output from the first optical path and the pulsed light output from the second optical path.

[0093] With this configuration, the phase characteristic calibration device according to the present invention has an optical BPF between the optical multiplexer / demultiplexer and the optical receiver. This expands the pulse width of both the pulse light output from the first optical path and the pulse light output from the second optical path. Since the optical BPF is provided to restrict the mode of the pulse light so that the light input to the optical receiver interferes, a CW light source is not required as light for the interferometer, and the complexity and cost-effectiveness of the optical system are improved compared to the conventional technology. In addition, compared to the configuration shown in FIG. 6, the optical demultiplexer 104 in FIG. 6 is not required, so the configuration of the optical system is simplified and the cost is reduced.

[0094] In the phase characteristic calibration device according to the present invention, the interferometer includes a first optical demultiplexer (103) that is provided at a branching point between the first optical path and the second optical path, demultiplexes the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputs the first pulsed light toward the first optical path, and outputs the second pulsed light toward the second optical path; a second optical demultiplexer (104) that is provided on the first optical path on the opposite side to the first optical demultiplexer with the variable delay device interposed therebetween, receives the first pulsed light that has passed through the variable delay, demultiplexes the input first pulsed light into a third pulsed light and a fourth pulsed light, and outputs the third pulsed light to the first optical path; The optical bandpass filter may be provided in a first optical path on the opposite side of the variable delay device side with the second optical demultiplexer therebetween or in the second optical path, and an optical combiner (105) is provided at a junction of the first optical path and the second optical path, and generates the interference light by combining a fifth pulse light output from the optical bandpass filter provided in one of the first optical path and the second optical path and a sixth pulse light output from the other of the first optical path and the second optical path, wherein the optical bandpass filter expands a pulse width of either the pulse light output from the first optical path or the pulse light output from the second optical path.

[0095] With this configuration, the impulse response of the optical BPF is not inversion symmetric with respect to time, so the interference signal is not positive-negative symmetric with respect to zero optical path length difference. Therefore, the delay amount (optical path difference) L is L=c / 2f rep Even when the interference signal is not zero (f rep is the repetition frequency of the pulsed light. This makes it possible to correct variable delay devices with long delay amounts.

[0096] In the phase characteristic calibration device according to the present invention, the interferometer includes a first optical demultiplexer (103) that is provided at a branching point between the first optical path and the second optical path, demultiplexes the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputs the first pulsed light toward the first optical path, and outputs the second pulsed light toward the second optical path; a second optical demultiplexer (104) that is provided on the first optical path on the opposite side to the first optical demultiplexer across the variable delay device, receives the first pulsed light that has passed through the variable delay device, demultiplexes the input first pulsed light into a third pulsed light and a fourth pulsed light, and outputs the third pulsed light to the first optical path; and a first optical band splitter (105) that is provided on the first optical path on the opposite side to the variable delay device across the second optical demultiplexer, receives the third pulsed light, and outputs a fifth pulsed light. a sixth optical bandpass filter (108A) provided in the second optical path, receiving the second pulsed light and outputting a sixth pulsed light; and an optical combiner (105) provided at a junction of the first optical path and the second optical path, combining the fifth pulsed light outputted from the first optical bandpass filter and the sixth pulsed light outputted from the second optical bandpass filter to generate the interference light, wherein the optical bandpass filter includes the first optical bandpass filter (108A) and the second optical bandpass filter (108B), the first optical bandpass filter expands the pulse width of the pulsed light outputted from the first optical path, and the second optical bandpass filter expands the pulse width of the pulsed light outputted from the second optical path.

[0097] With this configuration, the phase characteristic calibration device according to the present invention divides the optical BPF into two, the first optical BPF and the second optical BPF, and places them on both optical paths. This expands the pulse width of both the pulse light output from the first optical path and the pulse light output from the second optical path. Since the optical BPF is provided to limit the mode of the pulse light so that the light input to the photodetector interferes, a CW light source is not required for the interferometer as light for the interferometer, and the complexity and cost-effectiveness of the optical system are improved compared to the conventional technology. Line spectrum components that pass only one optical BPF do not interfere after combining, and only line spectrum components that pass two optical BPFs interfere. Therefore, by configuring the first optical BPF and the second BPF with etalons with different FSRs or configuring them with an etalon and a wavelength filter, the FSR of the etalon does not need to be large, that is, the finesse does not need to be high. Therefore, the optical BPF can be realized relatively easily.

[0098] In the phase characteristic calibration device according to the present invention, the optical multiplexer may be an optical multiplexer / demultiplexer (105B) that multiplexes the fifth pulse light and the sixth pulse light to generate a first interference light and a second interference light as the interference light, and the optical receiver may be a differential optical receiver (106A) that receives the first interference light and the second interference light and differentially detects intensities of the interference lights.

[0099] With this configuration, the phase characteristic calibration device according to the present invention can eliminate in-phase noise, increase the intensity of the interference signal, and improve the S / N ratio. In addition, by detecting the zero-crossing point, it is possible to extract phase information without being affected by amplitude fluctuations.

[0100] In the phase characteristic calibration device according to the present invention, the optical multiplexer may be an optical multiplexer / demultiplexer (105B) that multiplexes the fifth pulse light and the sixth pulse light to generate a first interference light and a second interference light as the interference light, and the optical receiver may be a differential optical receiver (106A) that receives the first interference light and the second interference light and differentially detects intensities of the interference lights.

[0101] With this configuration, the phase characteristic calibration device according to the present invention can eliminate in-phase noise, increase the intensity of the interference signal, and improve the S / N ratio. In addition, by detecting the zero-crossing point, it is possible to extract phase information without being affected by amplitude fluctuations.

[0102] A phase characteristic calibration method according to the present invention includes splitting pulse light having a predetermined repetition frequency by an optical splitter (3), multiplexing three or more intermediate frequency signals having different frequencies, outputting a multi-tone intermediate frequency signal modulated by a reference signal, up-converting the multi-tone intermediate frequency signal using a local signal having a predetermined frequency and a frequency conversion unit (21) to generate a calibration signal, controlling the frequencies of the three or more intermediate frequency signals and the local signal using one of the pulse lights output from the optical splitter so that the frequency of each of the up-converted intermediate frequency signals included in the calibration signal becomes an integer multiple of the repetition frequency of the pulse light, sampling the calibration signal by an electro-optic effect using the other of the pulse lights output from the optical splitter, and outputting the calibration signal as an electrical signal, and using a variable delay device to which one or the other of the pulse lights output from the optical splitter is input, the calibration signal is used for sampling the calibration signal. and acquiring the electrical signal while changing a relative time difference between the pulsed light and the calibration signal, modulating the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the intermediate frequency signal of three or more waves contained in the electrical signal, inputting CW light to a first optical path including the variable delay device and a second optical path not including the variable delay device, causing the CW light output from the first optical path to interfere with the CW light output from the second optical path, outputting the interfered light as an interference signal, detecting an intensity of the interfered light as an interference signal, sampling the multi-tone signal according to a signal obtained by dividing a frequency of the interfered signal to generate a corrected multi-tone signal, detecting a phase difference between three or more tone signals corresponding to the intermediate frequency signal of three or more waves contained in the corrected multi-tone signal, and calculating a phase difference between the three or more tone signals from a phase difference between the tone signals.73), and calculating a phase correction value for correcting the phase frequency characteristic of the down-converter of the signal measuring unit that down-converts and measures the signal under test, the method for calibrating the phase frequency characteristic of the down-converter of the signal measuring unit is characterized in that the pulsed light input to the variable delay device is used instead of the CW light, and optical bandpass filtering is performed to expand the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

[0103] With this configuration, the phase characteristic calibration method according to the present invention performs optical bandpass filtering to expand the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other when correcting the phase frequency characteristic of the downconverter of the signal measurement unit that downconverts and measures the signal under test. This makes it unnecessary to use a CW light source in generating the interference light, and improves the complexity and cost-effectiveness of the optical system compared to the conventional techniques shown in Figures 31 and 32.

[0104] A phase characteristic calibration method according to the present invention includes splitting pulse light having a predetermined repetition frequency by an optical splitter (3), multiplexing three or more intermediate frequency signals having different frequencies, generating a multi-tone intermediate frequency signal modulated by a reference signal, up-converting the multi-tone intermediate frequency signal by an up-converter (84) of a signal generating unit (80) using a local oscillator signal having a predetermined frequency to generate a calibration signal, controlling the frequencies of the three or more intermediate frequency signals and the local oscillator signal by using one of the pulse lights output from the optical splitter so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulse light, sampling the calibration signal by an electro-optic effect using the other of the pulse lights output from the optical splitter, and outputting the calibration signal as an electrical signal, obtaining the electrical signal while changing the relative time difference between the pulse light used for sampling the calibration signal and the calibration signal by a variable delay device to which one or the other of the pulse lights output from the optical splitter is input, and modulating the electrical signal with a sine wave having the same frequency as the reference signal, a first optical path including the variable delay unit and a second optical path not including the variable delay unit, causing the CW light output from the first optical path to interfere with the CW light output from the second optical path and outputting the interfered light, detecting the intensity of the interfered light as an interfered signal, sampling the multi-tone signal according to a signal obtained by dividing the frequency of the interfered signal to generate a compensated multi-tone signal, and a phase correction value for correcting the phase-frequency characteristic of the up-converter of the signal generating unit, which up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, comprising: detecting a phase difference between three or more tone signals corresponding to the first and second optical paths; and calculating a phase correction value for correcting the phase-frequency characteristic of the up-converter of the signal generating unit from the phase difference between the tone signals;The present invention is characterized in that optical bandpass filtering is performed to expand the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path.

[0105] With this configuration, the phase characteristic calibration method according to the present invention performs optical bandpass filtering to expand the pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other when correcting the phase frequency characteristic of the up-converter of the signal generating unit that up-converts the measurement intermediate frequency signal and outputs it as a measurement signal. This makes it unnecessary to use a CW light source in generating the interference light, and improves the complexity and cost-effectiveness of the optical system compared to the conventional techniques shown in Figs. 33 and 34. Effect of the Invention

[0106] According to the present invention, it is possible to provide a phase characteristic calibration device and a phase characteristic calibration method that do not require a CW light source in an interferometer and are highly cost-effective. [Brief description of the drawings]

[0107] [Figure 1] FIG. 1 is a diagram for explaining an electro-optic sampling method. [Diagram 2] FIG. 2A is a timing chart of the signals in FIG. 1, and FIG. 2B is a diagram showing how waveform information is acquired by measuring an electric field while changing a delay time. [Diagram 3] 1A is a diagram showing a conventional configuration example, FIG. 1B is a diagram showing a configuration example of the main part of the present invention, and FIG. 1C is a diagram showing an interference signal of FIG. [Figure 4] 1 is a diagram showing an example of the overall configuration of a phase characteristic calibration device according to the present invention; [Diagram 5] 1 is a configuration diagram of a phase characteristic calibration device according to a first embodiment of the present invention. [Figure 6] FIG. 6 is a diagram illustrating the configuration of the interferometer in FIG. 5. [Figure 7]FIG. 1A shows an example in which an optical BPF is configured by combining two etalons, and FIG. 1B shows an example in which an optical BPF is configured by combining an etalon and a wavelength filter. [Figure 8] FIG. 13 is a diagram showing wavelength selectivity by a combination of multiple etalons. [Figure 9] FIG. 1A is a diagram for explaining wavelength selectivity obtained by combining two etalons, and FIG. 1B is a diagram for explaining wavelength selectivity obtained by combining an etalon and a wavelength filter. [Figure 10] FIG. 13 is a diagram showing changes in the number and intensity of modes passing through an optical BPF when frequency drift occurs in a pulsed laser used as a short-pulse light source. [Figure 11] FIG. 13 is a diagram showing a phase change of an interference signal due to a frequency drift of a pulsed laser serving as a short pulse light source. [Figure 12] Graphs (a-1), (b-1), and (c-1) show the change in amplitude of an interference signal due to frequency drift of a pulsed laser, and graphs (a-2), (b-2), and (c-2) show the relationship between the amount of delay and the amplitude of the interference signal. [Figure 13] 11 is a diagram showing the relationship between the delay time and the amplitude of an interference signal when the passband width is changed. FIG. [Figure 14] FIG. 11 is another configuration diagram of the interferometer (Modification 1). [Figure 15] FIG. 11 is another configuration diagram of the interferometer (Modification 2). [Figure 16] FIG. 1(a) shows a phase change of an interference signal due to frequency drift of a pulsed laser when an optical BPF is placed only on one of the optical paths, and FIG. 1(b) shows the relationship between the amount of delay and the amplitude of the interference signal. [Figure 17] FIG. 11 is another configuration diagram of the interferometer (Modification 3). [Figure 18] FIG. 13 is another configuration diagram of the interferometer (Modification 4). [Figure 19] FIG. 13 is a diagram showing another configuration of the interferometer (Modification 5). [Figure 20] FIG. 11 is a configuration diagram of a phase characteristic calibration device according to a second embodiment of the present invention. [Figure 21]FIG. 11 is a configuration diagram of a phase characteristic calibration device according to a third embodiment of the present invention. [Figure 22] FIG. 11 is a configuration diagram of a phase characteristic calibration device according to a fourth embodiment of the present invention. [Diagram 23] FIG. 13 is a configuration diagram of a phase characteristic calibration device according to a fifth embodiment of the present invention. [Figure 24] FIG. 13 is a configuration diagram of a phase characteristic calibration device according to a sixth embodiment of the present invention. [Diagram 25] FIG. 13 is a configuration diagram of a phase characteristic calibration device according to a seventh embodiment of the present invention. [Figure 26] FIG. 13 is a configuration diagram of a phase characteristic calibration device according to an eighth embodiment of the present invention. [Figure 27] 1 shows a first configuration example of a conventional phase characteristic calibration device. [Figure 28] 1 shows a second configuration example of a conventional phase characteristic calibration device. [Figure 29] 13 shows a third configuration example of a conventional phase characteristic calibration device. [Diagram 30] 13 shows a fourth configuration example of a conventional phase characteristic calibration device. [Diagram 31] 13 shows a fifth configuration example of a conventional phase characteristic calibration device. [Diagram 32] 13 shows a sixth example of the configuration of a conventional phase characteristic calibration device. [Diagram 33] 13 shows a seventh example of the configuration of a conventional phase characteristic calibration device. [Diagram 34] 13 shows an eighth configuration example of a conventional phase characteristic calibration device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0108] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0109] (Basic configuration) 3(a) is a diagram showing a configuration example of a conventional device, and (b) and (c) are diagrams showing configuration examples of the main parts of a phase characteristic calibration device according to an embodiment of the present invention. As shown in FIG. 3(a), in the conventional device in which an optical variable delay device 4 is disposed between an optical branching device 3 and a synchronization processing unit 5, a short pulse light output from a short pulse light source 2 passes through the optical variable delay device 4 and is input to a high-speed photodiode (PD) 5a of the synchronization processing unit 5.

[0110] When the optical variable delay device 4 is disposed between the optical splitter 3 and the synchronization processing unit 5, the phase characteristic calibration device according to the embodiment of the present invention is configured to include an interferometer 110, an optical receiver 106, a frequency divider 107, and an A / D converter 111 in addition to the configuration of the conventional device in FIG. 3(a), as shown in FIG. 3(b). The interferometer 110 includes a splitter 103, a splitter 104, a multiplexer 105, and an optical BPF 108, and multiplexes short pulse light through an optical path that passes through the optical variable delay device 4 and an optical path that does not pass through the optical variable delay device 4. An optical BPF 108 that restricts the short pulse light mode and generates interference light is provided between the multiplexer 105 and the optical receiver 106 of the interferometer 110. If one mode is passed from the pulse light to generate CW light, delay correction using CW light in the conventional technology is possible. However, the present invention is not limited to this, and also includes a case where multiple modes are passed from the pulse light. The optical BPF 108 has an impulse response longer than the delay caused by the optical path difference of the interferometer. Therefore, the pulse light passing through the optical BPF 108 interferes. The length of the impulse response of the optical BPF needs only to be longer than the time difference corresponding to the optical path difference of the interferometer including the delay device for correction. The intensity of the interference light is detected by the photoreceiver 106 and output as an interference signal, which is divided by the frequency divider 107 and used as a clock signal for A / D conversion of the electro-optic sampling signal by the A / D converter 111. FIG. 3(c) shows the waveform of the interference signal when the horizontal axis is the optical path difference ΔL and the vertical axis is the signal intensity. The interference signal is a sinusoidal repetitive signal in which the intensity of the interference signal is maximized when the optical path difference ΔL is an integer multiple of the center wavelength λ of the mode of the short pulse light passing through the optical BPF 108.

[0111] 4 is a diagram showing an example of the overall configuration of a phase characteristic calibration device according to an embodiment of the present invention in the case where an optical variable delay device 4 is disposed between an optical branching device 3 and a synchronization processing device 5. As shown in FIG. 4, the phase characteristic calibration device includes a short pulse light source 2, an optical variable delay device 4, a synchronization processing device 5 (including a high-speed PD 5a and a PLL 5b), a calibration signal generating unit 20 having a millimeter-wave tone signal generator, and an electro-optic sampling unit 30 (including an electro-optic probe 30a and a polarization detector 30b) as the same configuration as the conventional device. The phase characteristic calibration device of this embodiment further includes an interferometer 110 (including an optical splitter 103, an optical splitter 104, an optical multiplexer 105, and an optical BPF 108), an optical receiver 106 such as a low-speed PD, a frequency divider 107, and an A / D converter 111, and an optical BPF 108 is provided between the optical multiplexer 105 and the optical receiver 106 of the interferometer 110.

[0112] The short pulse light source 2 is, for example, a fiber laser that outputs short pulse light at a predetermined repetition frequency. The short pulse light that passes through the optical branching device 103 and the variable optical delay device 4 is sent to the synchronization processing device 5 via the optical branching device 104. In the synchronization processing device 5, the short pulse light is converted into an electric signal by a photoreceiver such as a high-speed PD 5a, and sent to the PLL 5b, where synchronization processing is performed on the millimeter-wave multi-tone signal generated by the calibration signal generating device 20. The multi-tone signal is sent to the electro-optic sampling device 30, and electro-optic sampling of the millimeter-wave multi-tone signal is performed using the short pulse light that is output from the short pulse light source 2 and branched by an optical branching device (not shown) without passing through the variable optical delay device 4.

[0113] In the interferometer 110, short pulse light is input to a first optical path including the optical variable delay device 4 and a second optical path not including the variable delay device 4, the short pulse light output from the first optical path is combined with the short pulse light output from the second optical path, the pulse width of the two pulse lights is expanded by the optical BPF so that the two pulse lights interfere with each other, and the interferometer 110 outputs the two pulse lights as interference light. For example, the short pulse light output from the short pulse light source 2 made of a pulse laser is split by the optical splitter 103, one of which is sent to the optical variable delay device 4 and the other is sent to the optical multiplexer 105. The short pulse light that has passed through the optical variable delay device 4 is sent to the optical multiplexer 105 via the optical splitter 104, and is combined with the short pulse light sent from the optical splitter 103 side by the optical multiplexer 105. The combined light is input to the optical BPF to expand the pulse width of the pulse light and output as interference light. This causes interference between the short pulse light that has passed through the optical variable delay device 4 and the short pulse light that has not passed through the optical variable delay device 4. The interference light is light consisting of a mode of the short pulse light limited by the optical BPF 108. The intensity of the interference light is detected by the photoreceiver 106 and sent to the frequency divider 107 as an interference signal. The interference signal is divided by the frequency divider 107 and used as a clock signal (trigger) for A / D conversion of the electro-optic sampling signal in the A / D converter 111. The interference signal is, for example, a sinusoidal repetitive signal that has a peak when the optical path length difference (delay time) is equal to an integer multiple of the central wavelength λ (period) of the mode of the short pulse light that passes through the optical BPF 108. Therefore, the multi-tone signal obtained by the electro-optic sampling is sampled at a constant interval with respect to the delay amount regardless of the sweep speed of the optical variable delay device 4. This makes it possible to correct the phase fluctuation of the millimeter-wave multi-tone signal caused by the instability of the sweep speed of the optical variable delay device 4.

[0114] (First embodiment) 5 is a configuration diagram of a phase characteristic calibration device 1 according to a first embodiment of the present invention. The phase characteristic calibration device 1 corrects the phase frequency characteristics of a down converter (frequency conversion unit 72, intermediate frequency signal conversion unit 73) of a millimeter wave band signal measurement unit 70 that performs frequency conversion (down conversion) on a signal to be measured and measures it. For this purpose, the phase characteristic calibration device 1 includes a short pulse light source 2, an optical branching unit 3, an optical variable delay unit 4, a calibration signal generation unit 20, a synchronization processing unit 5, an electro-optic sampling unit 30, a lock-in detection unit 40, a multi-tone phase difference measurement unit 50, a phase correction value calculation unit 55, and a delay amount correction unit 100 for correcting the amount of delay caused by the optical variable delay unit 4.

[0115] The millimeter waveband signal measuring unit 70, the short pulse light source 2, and the optical variable delay unit 4 in this embodiment correspond to the signal measuring unit, the pulse light source, and the variable delay unit of the present invention, respectively, and the three-tone intermediate frequency signal generating unit 10 and the reference signal modulating unit 17 in this embodiment correspond to the multi-tone intermediate frequency signal generating unit of the present invention.

[0116] The short pulse light source 2 outputs a short pulse light P1 at a predetermined repetition frequency. Specifically, for example, a mode-locked fiber laser generates a short pulse light P1 with a repetition frequency of 100 MHz and a pulse width of about 100 fs. The short pulse light P1 output from the short pulse light source 2 is branched by an optical brancher 3 into two short pulse lights P2 and P3. The short pulse light P2 is input to an optical variable delay device 4 via an optical demultiplexer 103, and the short pulse light P3 is input to a synchronization processing unit 5.

[0117] The variable optical delay device 4 continuously changes the delay time of the light by mechanically moving the position of the mirror 4a. The short pulse light P4 output from the variable optical delay device 4 is input to the electro-optic sampling unit 30 via the optical splitter 104.

[0118] In this embodiment, the optical variable delay unit 4 is disposed between the optical splitter 3 and the electro-optic sampling unit 30, but is not limited to this arrangement. The optical variable delay unit 4 divides the short pulse light P4 input to the electro-optic sampling unit 30 and the calibration signal S output from the calibration signal generating unit 20 and input to the electro-optic sampling unit 30. 20 Therefore, the variable optical delay device 4 may be placed between the optical splitter 3 and the synchronization processing unit 5.

[0119] When the switches SW11 and SW12 are set to the lower position in FIG. 5, the calibration signal generating unit 20 outputs a CW local oscillator signal S 22 is used to generate a modulated multi-tone intermediate frequency signal S 19 is up-converted to the millimeter wave frequency to generate the calibration signal S 20 For this purpose, the calibration signal generating section 20 includes a three-tone intermediate frequency signal generating section 10, a reference signal modulating section 17, a local oscillator signal generating section 22, and a frequency converting section 21.

[0120] The intermediate frequency signal generators 11a to 11c of the three-tone intermediate frequency signal generating unit 10 generate sine waves (intermediate frequency signals S1, S2, S3) of different frequencies with a predetermined phase difference, and the three sine waves are added together in an adder 15 to generate a multi-tone intermediate frequency signal S. 10 The output is as follows:

[0121] The reference signal generator 18 of the reference signal modulation unit 17 receives the reference synchronization signal S 16 According to the above, a reference signal S with a frequency lower than that of each of the three sine waves is 18 The modulator 19 generates a multi-tone intermediate frequency signal S 10 Let S be the reference signal. 18 and modulating the modulated multi-tone intermediate frequency signal S 19 The reference synchronization signal S 16 may or may not be synchronized with the repetition frequency of the short pulse light source 2.

[0122] The modulated multi-tone intermediate frequency signal S, which is the output signal from the reference signal modulation unit 17, 19 is up-converted to a millimeter wave frequency by the local signal generator 22 and the frequency converter 21 to generate a calibration signal S 20 When the switches SW1 and SW2 are set to the upper side in FIG. 5, the calibration signal S 20 The phase difference is measured.

[0123] The synchronization processor 5 receives the multi-tone intermediate frequency signal S 10 and the local oscillator signal S 22 and the repetition frequency of the short pulse light source 2, a millimeter wave calibration signal S synchronized with the repetition frequency of the short pulse light source 2 is generated. 20 Specifically, the synchronization processing unit 5 receives the short pulse light P3 output from the optical splitter 3 and outputs the calibration signal S 20 is an integer multiple of the repetition frequency of the short pulse light P3, and the phases of the up-converted intermediate frequency signals at the pulse timing of the short pulse light P3 are constant. 22 The frequency of the input signal is controlled by the oscilloscope.

[0124] Specifically, the synchronization processing unit 5 uses a phase-locked loop (PLL) circuit to synchronize the local oscillator signal S output from the local oscillator signal generating unit 22. 22 and the frequency of each of the sine waves output from the intermediate frequency signal generators 11a to 11c are set to an integer multiple of the repetition frequency of the short pulse light source 2, and the local signal S at the pulse timing of the short pulse light P3 is set to 22 The local signal generating unit 22 and the voltage controlled oscillators (VCOs) in the intermediate frequency signal generators 11a to 11c are controlled so that the phases of the sine waves output from the intermediate frequency signal generators 11a to 11c are constant. 20 The repetition frequency of this pulse is an integer multiple of the repetition frequency of the short pulse light source 2.

[0125] The calibration signal S is obtained by using the electro-optic sampling unit 30. 20 When measuring the phase difference, the switches SW1 and SW2 are set to the upper positions in FIG.

[0126] The electro-optic sampling unit 30 outputs a calibration signal S 20 The electric field is applied to the electro-optic crystal 31, and linearly polarized short pulse light P4 from the variable optical delay device 4 is input to the electro-optic crystal 31 via the polarization separator 32, and the short pulse light reflected at the tip of the electro-optic crystal 31 is input to the optical receiver 33 via the polarization separator 32. When an electric field is applied to the electro-optic crystal 31, the polarization of the reflected light from the electro-optic crystal 31 changes due to the electro-optic effect, and the polarization change of the reflected light is detected by the polarization separator 32 and the optical receiver 33 to produce an electrical signal S 30 The electrical signal S output from the optical receiver 33 is 30 is proportional to the electric field applied to the electro-optic crystal 31 and also to the optical power of the short pulse light P4.

[0127] The pulse width of the short pulse light P1 is calibrated by the calibration signal S 20 If the frequency is made sufficiently shorter than half the reciprocal of the maximum frequency of the electrical signal S 30 is the calibration signal S 20 The repetition period of the short pulse light source 2 is the same as the calibration signal S 20 Since it is an integer multiple of the repetition period of the calibration signal S 20 By changing the delay time of the optical variable delay device 4, the calibration signal S 20 Since the time when the short pulse light P4 is sampled changes, the delay time of the variable optical delay device 4 is swept while the electrical signal S from the electro-optic sampling unit 30 is sampled. 30 When this is recorded, the millimeter-wave calibration signal S is generated by the low-speed receiver 33. 20 The time waveform can be measured.

[0128] In general, the electrical signal S from the electro-optic sampling unit 30 30Since the phase characteristic calibration device 1 shown in FIG. 5 is very small, a reference signal modulation section 17 is provided in the calibration signal generation section 20 to generate a reference signal S 18 The lock-in detector 40 is provided after the electro-optic sampling unit 30 to obtain a reference signal S 41 The lock-in detection is performed by the

[0129] The reference signal generator 18 of the reference signal modulation unit 17 receives the reference synchronization signal S 16 According to the above, a reference signal S with a frequency lower than that of each of the three sine waves is 18 The modulator 19 generates a multi-tone intermediate frequency signal S 10 Let S be the reference signal. 18 and modulating the modulated multi-tone intermediate frequency signal S 19 The reference synchronization signal S 16 may or may not be synchronized with the repetition frequency of the short pulse light source 2.

[0130] The output signal S from the reference signal modulation unit 17 19 is up-converted to a millimeter wave frequency by the local signal generator 22 and the frequency converter 21 to generate a calibration signal S 20 When the switches SW1 and SW2 are set to the upper side in FIG. 5, the calibration signal S 20 The phase difference is measured.

[0131] The electrical signal S from the electro-optic sampling unit 30 30 is input to the lock-in detection unit 40. The reference signal generator 41 of the lock-in detection unit 40 receives the reference synchronization signal S 17 According to the above, the reference signal S 18 A reference signal S, which is a sine wave of the same frequency as 41 The phase shifter 42 generates the reference signal S in the calibration signal sampled by the electro-optic sampling unit 30 in the modulator 44. 18 and the phase of the reference signal S 41The reference signal S 41 Adjust the phase of the reference signal S 42 The modulator 44 outputs the electrical signal S from the electro-optic sampling unit 30. 30 Let S be the reference signal. 42 and the low-frequency components are extracted by a low-pass filter 45.

[0132] In general, the cutoff frequency of the low-pass filter 45 is set to a value smaller than the reference signal S 41 The frequency of the electrical signal S from the electro-optic sampling unit 30 is lower than that of the signal S1 and is determined by the sweep speed of the variable optical delay unit 4. 30 The cutoff frequency of the low-pass filter 45 is set higher than any of the frequencies of the three-tone signals in. If the cutoff frequency of the low-pass filter 45 is lowered, the sweep speed of the variable optical delay device 4 must be slowed down, and measurement takes time, but the frequency band is narrowed and the signal-to-noise ratio is improved.

[0133] Normally, the phase detection sections 51a to 51c of the subsequent three-tone phase difference measurement section 50 have frequency selectivity for detecting the frequencies of the three tones, and the measurement band of the phase detection sections 51a to 51c is narrower than the band of the low-pass filter 45 of the lock-in detection section 40, so that the S / N ratio of the phase measurement is determined by the latter.

[0134] Therefore, the low-pass filter 45 of the lock-in detection section 40 should be set to a cutoff frequency appropriate for use as an anti-aliasing filter when A / D conversion is performed before the three-tone phase difference measurement section 50 as in this embodiment, or when the sampling rate is lowered to reduce the amount of calculation in the phase detection sections 51a to 51c.

[0135] The advantage of lock-in detection is that it detects a signal modulated by a reference signal, e.g., the reference signal S 18 By setting the frequency to several MHz, the effects of DC drift and 1 / f noise of photodetector 33 of electro-optic sampling unit 30 can be avoided, and measurement sensitivity can be improved even if phase detection units 51a to 51c have the same measurement band.

[0136] The output signal from lock-in detection section 40 is input to A / D converter 111 of multi-tone signal sampling section 120 provided in delay amount correction section 100 (described later), converted to a digital signal, and output as a corrected multi-tone signal. The output signal from A / D converter 111 is input to three-tone phase difference measurement section 50.

[0137] The three-tone phase difference measurement unit 50 detects the phase of each tone by digital signal processing, and calculates the phase difference. 30 The phase of the first tone of the three tones in the intermediate frequency signal generators 11a to 11c is detected. Similarly, phase detector 51b and phase detector 51c detect the phases of the second tone and the third tone, respectively. Here, the phase difference between the sine waves generated by intermediate frequency signal generators 11a to 11c may be corrected.

[0138] Generally, in phase measurement of a high-frequency signal, the absolute phase and the frequency slope of the phase are indefinite, so the phase difference calculation unit 52 calculates the second-order differential of each phase of the three tones and outputs it as the phase difference measurement result using the electro-optic sampling unit 30. In order to calculate the second-order differential, the phases of at least three tones are required. The above processing is performed on the calibration signal S 20 The frequency of the three tones is changed and repeated to measure the second derivative of the phase over a predetermined frequency range. The frequency characteristic of the phase can be obtained by integrating the second derivative of the phase twice. 50 is output from the phase difference calculation unit 52.

[0139] When the switches SW1 and SW2 are set to the lower position in FIG. 5 and the switches SW3 and SW4 are set to the upper position in the same figure, the calibration signal S 20 The phase difference is measured.

[0140] In the millimeter wave band signal measuring section 70, a CW local oscillator signal S 71 and a frequency converter 72 such as a mixer to generate a millimeter-wave calibration signal S20 The local oscillator signal S is frequency converted (down-converted) to an intermediate frequency signal. 71 does not necessarily need to be synchronized with the short pulse light P1, but the local signal S 71 The synchronization processing unit 5 may control the local signal generating unit 71 so that the frequency of the intermediate frequency signal becomes an integer multiple of the repetition frequency of the short pulse light source 2. The intermediate frequency signal converting unit 73 may include a frequency converter for converting the intermediate frequency signal into a second intermediate frequency signal, an orthogonal frequency converter for converting the intermediate frequency signal into an I / Q signal, etc. The intermediate frequency signal converting unit 73 also includes an A / D converter for converting the intermediate frequency signal, the second intermediate frequency signal, or the I / Q signal into a digital signal, and outputs the digital signal to the three-tone phase difference measuring unit 50 or the phase correction unit 74.

[0141] The switches SW1 and SW2 are set to the lower position in FIG. 5, and the switches SW3 and SW4 are set to the upper position in FIG. 5, and the calibration signal S 20 When measuring the phase difference between the reference signal modulation unit 17 and the electro-optic sampling unit 30, the lock-in detection unit 40, and the A / D converter 111, the reference signal modulation unit 17 is not performed by setting the switches SW11 and SW12 to the upper side in FIG.

[0142] The output signal S from the intermediate frequency signal conversion unit 73 of the millimeter wave band signal measurement unit 70 70 is input to the three-tone phase difference measuring unit 50 via the switch SW2 from a path that bypasses the electro-optic sampling unit 30, the lock-in detection unit 40, and the A / D converter 111, and the electrical signal S 30 Similarly to the phase difference measurement in , the phase detection units 51a to 51c detect the phases of the three tones, and the phase difference calculation unit 52 calculates the second order differential of the phases of the three tones to obtain the calibration signal S 20 The frequency of the three tones is changed and repeated, and the second derivative of the phase is integrated twice to obtain the frequency characteristic of the phase. 50' will be output.

[0143] [Delay compensation section] Next, the delay amount correcting section 100 will be described.

[0144] The delay amount correction unit 100 corrects phase fluctuations in the multi-tone signal obtained by electro-optic sampling, which are caused by instability in the sweep speed of the optical variable delay unit 4, and as shown in Figures 5 and 6, it includes a short pulse light source 2, an interferometer 110 including an optical BPF 108, a photoreceiver 106, a frequency divider 107, and a multi-tone signal sampling unit 120.

[0145] In the interferometer 110, short pulse light is input to a first optical path OP1 including the optical variable delay device 4 and a second optical path OP2 not including the optical variable delay device 4, the short pulse light output from the first optical path OP1 and the short pulse light output from the second optical path OP2 are multiplexed, and output to the optical BPF 108. The optical BPF 108 expands the pulse width of the optical pulse and outputs interference light.

[0146] Specifically, the interferometer 110 includes an optical splitter 103 such as a half mirror, an optical splitter 104 such as a half mirror, an optical multiplexer 105, and an optical BPF 108. The optical splitter 103 is provided at the branch point of the first optical path OP1 and the second optical path OP2, and splits the short pulse light output from the short pulse light source 2 and passed through the optical splitter 3 into a first short pulse light and a second short pulse light. The first short pulse light is sent to the optical variable delay device 4 of the first optical path OP1, and the second short pulse light is sent to the optical multiplexer 105 through the second optical path OP2. The optical splitter 104 is provided on the first optical path OP1 on the opposite side to the optical splitter 103 side with the optical variable delay device 4 interposed therebetween, and receives the first short pulse light transmitted via the optical variable delay device 4, splits it into a third short pulse light and a fourth short pulse light, outputs the third short pulse light to the first optical path OP1 toward the optical multiplexer 105, and outputs the fourth short pulse light toward the electro-optic sampling unit 30. The optical multiplexer 105 is provided at the joining point of the first optical path OP1 and the second optical path OP2, and multiplexes the second short pulse light split by the optical splitter 103 and the third short pulse light split by the optical splitter 104 to generate a fifth pulse light. The fifth pulse light is input to an optical BPF, and an interference light is output by expanding the pulse width of the pulse light. That is, the third short pulse light that has passed through the variable optical delay device 4 and is demultiplexed by the optical demultiplexer 104 and the second short pulse light that has not passed through the variable optical delay device 4 and is sent from the optical demultiplexer 103 interfere with each other.

[0147] The spectrum of the short pulse light consists of many line spectra spaced apart by the repetition frequency, and when only one of these line spectra is extracted by the optical BPF 108, it becomes CW light, and interference light similar to that obtained by a conventional interferometer using CW light is obtained. When multiple line spectra are extracted by the optical BPF 108, CW light is not obtained, but the pulse width of the short pulse light is expanded by the optical BPF, and if the pulse width is longer than the propagation time difference due to the optical path length difference between the first and second optical paths, interference occurs and interference light is obtained. In other words, when ordinary short pulse light is simply combined by the combiner 105, the pulse width is shorter than the propagation time difference due to the optical path length difference between the first and second optical paths, and no interference occurs, but by providing an optical BPF 108 with an appropriate spectral width, interference light can be obtained using short pulse light.

[0148] The optical receiver 106 includes, for example, a low-speed photodiode, detects the intensity of the interference light that has passed through the optical BPF 108, and outputs it as an interference signal. The interference signal is a sinusoidal repetitive signal that reaches a peak when the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 is equal to an integer multiple of the central wavelength (period) of the interference light.

[0149] The frequency divider 107 divides the frequency of the interference signal output from the photoreceiver 106. If the division ratio of the frequency divider 107 is N (N is an integer), then the frequency divider 107 outputs a rectangular wave in which the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 rises every N times the central wavelength (period) of the interference light.

[0150] Multi-tone signal sampling section 120 samples the multi-tone signal output from lock-in detection section 40 in accordance with the output of frequency divider 107, and outputs the sampled multi-tone signal as a corrected multi-tone signal. Specifically, multi-tone signal sampling section 120 includes an A / D converter 111 that performs A / D conversion on the multi-tone signal detected by lock-in detection section 40, and the output signal of frequency divider 107 is used as an A / D conversion clock signal for A / D converter 111. For example, A / D converter 111 A / D converts the multi-tone signal at the rising edge of the output signal of frequency divider 107.

[0151] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at constant intervals relative to the delay amount, regardless of the sweep speed of the variable optical delay device 4. Since the center frequency of the interference light is about three orders of magnitude higher than the frequency of the millimeter-wave multi-tone signal, if an optical BPF with a relatively stable center frequency in the passband is used as the optical BPF 108, the phase fluctuation of the multi-tone signal obtained by electro-optic sampling, which is caused by the instability of the sweep speed of the variable optical delay device 4, can be corrected.

[0152] [Division ratio / oversampling ratio] The frequency of the interference signal is the frequency obtained by multiplying the center frequency of the interference light by the sweep rate of the optical variable delay device 4, and the frequency of the multi-tone signal obtained by the electro-optic sampling is the frequency obtained by multiplying the frequency of the millimeter wave signal by the sweep rate of the optical variable delay device 4. Since the center frequency of the interference light is about three orders of magnitude higher than the frequency of the millimeter wave signal, the frequency of the interference signal is about three orders of magnitude higher than the frequency of the multi-tone signal obtained by the electro-optic sampling. If the interference signal is used as it is as the A / D conversion clock, the sampling frequency will be higher than necessary, and a high-speed A / D converter and a large-capacity memory will be required. Therefore, if the division ratio of the frequency divider 107 is appropriately set and the output of the frequency divider 107 is used as the A / D conversion clock, a necessary and sufficient sampling frequency can be obtained.

[0153] The division ratio of the frequency divider 107 is N, and the center frequency of the interference light is f opt , the frequency of the millimeter wave signal is f rf If the oversampling ratio is r, the division ratio N is expressed by the following equation. N=f opt / 2rf rf (1) where f rfuses the highest tone frequency of the millimeter-wave tone signal. When r=1, it becomes the minimum sampling frequency that satisfies the sampling theorem. Normally, it is desirable to use oversampling such as r=2 or r=4. Oversampling relaxes the cutoff characteristic requirements of the low-pass filter 45 (which also serves as an anti-aliasing filter) of the lock-in detection unit 40.

[0154] For example, if the central wavelength of the interference light is 1550 nm, the frequency of the millimeter-wave signal is 300 GHz, and the oversampling ratio is 2, the division ratio is 161, which means that an A / D converter with a sampling frequency of 1 / 161 will be sufficient compared to the case where the interference signal is used directly as the A / D conversion clock.

[0155] [Optical BPF] Next, the optical BPF 108 will be described. 31 to 34 (the fifth to eighth configuration examples), an interference signal is generated using a CW light source 101. In this embodiment, the CW light source 101 is omitted by applying an optical BPF 108 to a short pulse light (short pulse laser light) used for electro-optic sampling.

[0156] The frequency resolution of the phase characteristic calibration device 1 is the repetition frequency f rep Therefore, the repetition frequency f rep It is desirable to keep it low (for example, 100 MHz). By using an etalon (a Fabry-Perot interferometer used as an optical BPF), it is in principle possible to extract one mode from a short pulse light. A mode refers to one of the frequency spectra of a short pulse light. If short pulse light is considered to be a collection of many CW lights, one mode is equivalent to CW light. Therefore, if one mode can be extracted from a short pulse light, it is possible to omit the CW light source 101.

[0157] The frequency f(n) of the n-th mode of a short pulse of light is given by the following equation: f(n)=nf rep +f ceo (2) where f rep is the repetition frequency of the short pulse light, f ceo is the carrier envelope offset frequency.

[0158] [assignment] There are three issues to be considered in the configuration in which one mode of short pulse light is extracted by the optical BPF 108: (1) It is difficult to realize an optical BPF with a narrow passband: To extract one mode, the passband width BW(BPF) of the optical BPF 108 is set to BW(BPF)< <f rep However, f rep Since it determines the limit of the resolution of the phase characteristic calibration, it cannot be a high frequency. Furthermore, it is necessary to tune the passband frequency of the optical BPF 108 to one mode of the short pulse light and stabilize the passband frequency (temperature control, etc.). If, as will be described later, an etalon and a wavelength filter are used together as the optical BPF, and an etalon with an FSR equivalent to the passband width of a realistic wavelength filter is used, then BW(BPF) = 10 MHz (< <f rep = 100 MHz), FSR = 150 GHz, and a mirror with a finesse of 15000 and a reflectivity of 99.98% are required. Such mirrors exist, but they are expensive and difficult to handle. (2) Difficulty in stabilizing the center frequency of the optical BPF: The center frequency of the optical BPF 108 must be sufficiently stable compared to the passband width. If the fluctuation is less than 1 MHz, -8 Frequency stabilization is required (FSR = 150 GHz, wavelength 1.5 μm). (3) Frequency stabilization of short pulse light sources is required: In order to suppress the frequency drift of the short pulse light, the short pulse light source 2 requires a complex system for stabilizing the frequency of each mode, but the same degree of stability as the optical BPF 108 is required. rep Frequency stabilization alone is not sufficient, and f ceo The frequency drift here refers to the frequency drift corresponding to the wavelength drift of each mode (f rep(not the frequency drift of the

[0159] [Consideration] The above three issues are considered under the following conditions. Repetition frequency of short pulse light f rep Assume that is very small compared to the frequency f of the short pulse light and the millimeter wave frequency. The passband width BW(BPF) of the optical BPF 108 is f rep For example, f = 200 THz (wavelength 1.5 μm), f rep =100MHz.

[0160] In this condition, two modes may pass through the optical BPF 108. rep When the mode passes through the optical bandpass filter 108, the interference signal is cos(2πfΔL / c)+cos{2π(f+f rep )ΔL / c} where ΔL is the optical path difference and c is the speed of light. rep Beats with a frequency equal to are also observed, but can be filtered out by a low-pass filter. Rewriting the above equation gives 2cos{2π(f+f rep / 2)ΔL / c}×cos{2π(f rep / 2)ΔL / c} It becomes.

[0161] The first term is the interference term, which is f rep The center frequency is different by f / 2, but the effect is very small when calculated as the phase of a millimeter wave. For example, when correcting the delay of 1 ns, f and f+f rep At / 2, the error is about 0.03 degrees when converted to a 300 GHz phase. The second term is the beat component, f rep Since ΔL is small, the change is very slow even if ΔL changes. In this example, the repetition wavelength is 3 m. If the optical path difference is sufficiently smaller than half of this repetition wavelength, the interference term can be observed without any problem. Under this condition, the passband of the optical BPF is f repTherefore, even if the frequency of the mode of the short pulse light drifts, one or more modes will exist in the transmitted light. Therefore, under the above conditions, if the optical BPF 108 is stabilized, the short pulse light can be used even in a free-running state.

[0162] [Feasibility of optical BPF] Next, we discuss the feasibility of narrow-band optical BPF. Repetition frequency f rep An optical BPF with a passband width of approximately the same frequency (e.g. 100 MHz) is required. Consider the case where this is realized by using an etalon and temperature stabilization. For example, the frequency spectrum width of a Fourier limit pulse width of 90 fs is about 5 THz (assuming the pulse shape is Gaussian). When converted to a wavelength, this equates to a width of about 40 nm centered at 1.55 μm. However, since a high finesse is required, it is difficult to realize an etalon with an FSR of 5 THz and a passband width of several 100 MHz.

[0163] Therefore, in this embodiment, the following two configurations are used as the optical BPF. (i) Combining multiple etalons with different FSRs (ii) Combining an etalon with a wavelength filter having a passband width comparable to the FSR of the etalon

[0164] Fig. 7(a) shows a configuration example (i), in which the optical BPF 108 is composed of a first etalon 108a and a second etalon 108b. Fig. 7(b) shows a configuration example (ii), in which the optical BPF 108 is composed of an etalon 108c and a wavelength filter 108d.

[0165] The pass frequency (resonant frequency) f of the etalon is f=mc / 2l, and the FSR (spacing of the resonant frequencies) is FSR=c / 2l, where l is the resonator length, c is the speed of light, and m is a natural number.

[0166] [(i) Combination of multiple etalons] The wavelength selectivity is improved by combining etalons with different FSRs (different cavity lengths l). Fig. 9(a) is an explanatory diagram of an optical BPF constructed by combining two etalons. As shown in Fig. 9(a), when FSR1 of etalon 1 and FSR2 of etalon 2 are different, the least common multiple of FSR1 and FSR2 becomes the FSR of the optical BPF. As a result, by combining multiple etalons with FSRs smaller than the frequency band of the short pulse light, the effective FSR can be made larger than the frequency band of the short pulse light, and it becomes possible to extract only a small number of modes of the short pulse light.

[0167] FIG. 8 shows the relationship between the frequency of the input light and the amplitude transmittance for an optical BPF composed of a combination of multiple etalons. FIG. 8(a) shows the frequency characteristics of an optical BPF composed of a combination of an etalon with a resonator length of 1 mm and an etalon with a resonator length of 1.06 mm (passband width BW=400 MHz). By using two etalons with an FSR of about 150 GHz, a small number of modes can be selected within the band of short pulse light, ±5 THz. The least common multiple of the two FSRs is the FSR of the optical BPF. FIG. 8(b) shows the frequency characteristics of an optical BPF composed of a combination of an etalon with a resonator length of 10 mm and an etalon with a resonator length of 10.6 mm (passband width BW=200 MHz). The FSR of these etalons is about 15 GHz. As shown in FIG. 8(b), depending on the finesse (linewidth), a weak passband can be created on the side in addition to the passband of the FSR period. This causes the amplitude fluctuation of the interference signal. However, this can be blocked by a high-pass filter, etc. Also, if differential light reception is used as in Modification 4 described later, there is no effect.

[0168] [(ii) Etalon + wavelength filter] Wavelength filters with a passband width of several tens of GHz include products that use Bragg reflectors or diffraction gratings. When used in combination with an etalon with a similar FSR, an optical BPF can be realized that can extract a small number of modes of short pulse light.

[0169] Figure 9(b) is an explanatory diagram of an optical BPF constructed by combining an etalon and a wavelength filter. As shown in Figure 9(b), if wavelength filtering is performed on a signal that has passed through an etalon with multiple resonance frequencies with high transmittance, a signal with one of the etalon's resonance frequencies can be extracted. As a result, by combining an etalon with an FSR smaller than 1 / 2 the frequency band of a short pulse light with a wavelength filter, it becomes possible to extract only a small number of modes of the short pulse light.

[0170] [Frequency drift of pulsed laser] f rep By setting the frequency of the pulsed laser as 0 Hz, it is possible to extract one mode of the short pulsed light using the optical BPF. However, a realistic narrowband optical BPF (etalon) has a passband characteristic resembling a Lorentz curve (not rectangular) as shown in Fig. 10. Therefore, the number and strength of the modes passing through the optical BPF change when the frequency of the pulsed laser serving as the short pulsed light source 2 drifts. Fig. 10(a) shows the passband characteristic of the etalon when the frequency drift of the pulsed laser is 0 Hz, and Fig. 10(b) shows the passband characteristic of the etalon when the frequency drift is 50 MHz. In Fig. 10, the vertical lines indicate each mode of the short pulsed light. As shown in Fig. 10, when the frequency of the pulsed laser drifts, the number and strength of the modes passing through the etalon change.

[0171] FIG. 11 is a diagram showing the relationship between the frequency drift (horizontal axis) of the pulse laser as the short-pulse light source 2 and the phase (vertical axis) of the interference signal. FIG. 11(a) shows the passband width BW(BPF) of the optical BPF=f rep In the case of Fig. 11(b), BW(BPF)=2f rep In the case of Fig. 11(c), BW(BPF)=4f rep The pulse laser repetition rate f repWe assumed an optical BPF of etalon + wavelength filter under the conditions of = 100 MHz, etalon length l = 1 mm (FSR = 150 GHz), and wavelength filter width 100 GHz (rectangle). As shown in Figure 11, the narrower the BW (BPF), the larger the phase fluctuation. Delay amount L < 1.5 m (c / 2f rep If this is possible, then even if the frequency of the short-pulse light mode drifts, the phase of the interference signal will not change discontinuously.

[0172] 12(a-1), (b-1), and (c-1) are diagrams showing the change in amplitude of the interference signal due to the frequency drift of the pulse laser as the short-pulse light source 2. FIG. 12(a-1) shows the passband width BW(BPF)=f rep In the case of Fig. 12(b-1), BW(BPF)=2f rep In the case of Fig. 12(c-1), BW(BPF)=4f rep When the center frequency of the optical BPF and the frequency of a certain mode of the pulse laser are the same, the interference signal from that mode is large. However, when there is a short pulse light mode symmetrical to the center frequency of the optical BPF, the amplitudes of the interference signals of the modes symmetrical to the center frequency of the optical BPF are equal, and the delay amount L is L=c / 2f rep = 1.5m, the phases are reversed and cancel each other out. Figures 12(a-2), (b-2), and (c-2) show the relationship between the delay amount L and the amplitude of the interference signal when the optical variable delayer 4 is swept in a situation where there are short pulse light modes symmetrical with respect to the center frequency of the passband of the optical BPF. As shown in Figures 12(a-2), (b-2), and (c-2), the delay amount L = c / 2f rep When the optical BPF has a wide passband (BW) (i.e., many modes pass through), the amplitude of the interference signal increases.

[0173] As mentioned above, the delay L=c / 2f repAt 1.5 m, the amplitude of the interference signal becomes zero and the phase changes discontinuously, so it must be avoided, and it is also desirable to avoid the vicinity of that point. The phase fluctuation of the interference signal is very small when converted to millimeter waves. Even with a delay of 1.4 m, it is within ±50 degrees. Therefore, the phase conversion for a 300 GHz millimeter wave signal is ±0.08 degrees. When the passband width of the optical BPF is wide and many modes pass through, the amplitude fluctuation becomes large. That is, when the delay time is small, the interference signal is large, but when the delay time is large, the interference signal becomes small. Figure 13 is a diagram showing the relationship between the delay time and the amplitude of the interference signal when the passband width BW of the optical BPF is changed (when the frequency drift of the pulse laser as the short pulse light source 2 is 50 MHz). As shown in Figure 13, there is an appropriate passband width BW of the optical BPF for the delay time to be corrected. For example, when the delay time is 1 ns or less, the interference signal becomes larger when the passband width of the optical BPF is 400 MHz compared to when it is 100 MHz or 200 MHz. Therefore, it is desirable to select an appropriate passband width BW of the optical BPF depending on the dynamic range of the PD of the optical receiver 106 and the delay time to be corrected.

[0174] This embodiment is intended to solve the above three problems. (1) Passband width of optical BPF The passband width of the optical BPF does not need to be as narrow as 10 MHz, but can be around 100 MHz or 400 MHz. When using a wavelength filter and an etalon with an FSR of 150 GHz, which is narrower than the frequency band of short pulse light, as the optical BPF, the reflectivity of the etalon mirror can be 99.8% or 99.2% (cavity length 1 mm). (2) Stabilization of optical BPF The condition for stability of the passband frequency of the optical BPF is relaxed. The passband frequency drift of the optical BPF becomes the phase drift of the interference signal. For example, when the frequency drift is 500 MHz (3.75 pm@λ=1.5 μm), assuming a delay time of 1 ns, the phase change of the interference signal is less than 0.3 degrees at 300 GHz. Therefore, the frequency stability required for the optical BPF is 10 -6 That'll be fine. (3) Stabilization of short pulse light If the optical BPF is stabilized, there is no need to stabilize the frequency of the short pulse light. rep Since it has a spectrum of intervals, f ceo F rep Once the frequency drifts across the board, it will return to normal.

[0175] Note that the interferometer 110 according to this embodiment may be configured to use optical fiber for all or part of the optical path, or may be configured to set the optical path in free space such as air without using optical fiber for the optical path.

[0176] <Variation 1> Another example of the configuration of the interferometer will be described with reference to FIG.

[0177] The interferometer 110A in FIG. 14 includes an optical splitter 103 provided at the branching point of the first optical path OP1 and the second optical path OP2, an optical multiplexer / demultiplexer 105A provided at the joining point of the first optical path OP1 and the second optical path OP2, and an optical BPF 108.

[0178] In the interferometer 110A, short pulse light is input to a first optical path OP1 including an optical variable delay device 4 and a second optical path OP2 not including an optical variable delay device 4, the short pulse light output from the first optical path OP1 and the short pulse light output from the second optical path OP2 are multiplexed, and output to the optical BPF 108. The optical BPF 108 expands the pulse width of the optical pulse and outputs interference light.

[0179] Specifically, the interferometer 110A includes an optical splitter 103 such as a half mirror, an optical multiplexer / demultiplexer 105A such as a half mirror, and an optical BPF 108. The optical splitter 103 splits the short pulse light output from the short pulse light source 2 and passing through the optical splitter 3 into a first short pulse light and a second short pulse light. The first short pulse light is sent to the optical variable delay device 4 of the first optical path OP1, and the second short pulse light is sent to the optical multiplexer / demultiplexer 105A through the second optical path OP2. The optical multiplexer / demultiplexer 105A multiplexes the first short pulse light that has passed through the optical variable delay device 4 and the second short pulse light split by the optical splitter 103 to generate a third short pulse light and a fourth short pulse light. The third short pulse light is input to the optical BPF 108. The optical BPF 108 expands the pulse width of the third short-pulse light multiplexed by the optical multiplexer / demultiplexer 105A to generate interference light. The fourth short-pulse light is sent toward the electro-optic sampling unit 30.

[0180] The spectrum of the short pulse light consists of many line spectra spaced apart by the repetition frequency, and when only one of these line spectra is extracted by the optical BPF 108, it becomes CW light, and interference light similar to that obtained by a conventional interferometer using CW light is obtained. When multiple line spectra are extracted by the optical BPF 108, CW light is not obtained, but the pulse width of the short pulse light is expanded by the optical BPF, and if the pulse width is longer than the propagation time difference due to the optical path length difference between the first and second optical paths, interference occurs and interference light is obtained. In other words, when ordinary short pulse light is simply multiplexed by the multiplexer / demultiplexer 105A, the pulse width is shorter than the propagation time difference due to the optical path length difference between the first and second optical paths, and no interference occurs, but by providing an optical BPF 108 with an appropriate spectral width, interference light can be obtained using short pulse light.

[0181] The optical receiver 106 includes, for example, a low-speed photodiode, detects the intensity of the interference light that has passed through the optical BPF 108, and outputs it as an interference signal. The interference signal is a sinusoidal repetitive signal that reaches a peak when the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 is equal to an integer multiple of the central wavelength (period) of the interference light that passes through the optical BPF 108.

[0182] The frequency divider 107 divides the frequency of the interference signal output from the photoreceiver 106. If the division ratio of the frequency divider 107 is N (N is an integer), then the frequency divider 107 outputs a rectangular wave in which the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 rises every N times the central wavelength (period) of the interference light.

[0183] The interferometer 110A in Fig. 14 has one less optical splitter and is therefore simpler in configuration than the interferometer 110 in Fig. 6. This interferometer 110A has the problem that short pulse light that has not passed through the optical variable delay device 4 is input to the electro-optic sampling unit. However, since the millimeter wave is always sampled with the same phase, it becomes DC, and this basically poses no problem for observing the millimeter wave.

[0184] <Variation 2> Another example of the configuration of the interferometer will be described with reference to FIG.

[0185] 15 includes an optical splitter 103 provided at the branching point of the first optical path OP1 and the second optical path OP2, an optical splitter 104 provided on the first optical path OP1 on the opposite side of the optical splitter 103 with the optical variable delay device 4 interposed therebetween, an optical BPF 108 provided on the second optical path OP2, and an optical multiplexer 105 provided at the joining point of the first optical path OP1 and the second optical path OP2. The optical BPF 108 may be provided on the first optical path OP1, preferably between the optical splitter 104 and the optical multiplexer 105.

[0186] The interferometer 110B is configured such that short pulse light is input to a first optical path OP1 including an optical variable delay device 4 and a second optical path OP2 not including an optical variable delay device 4, and causes the short pulse light output from the first optical path OP1 to interfere with the optical BPF passing light output from the second optical path OP2, and outputs the interference light.

[0187] Specifically, the optical splitter 103 is made of, for example, a half mirror and splits the short pulse light output from the short pulse light source 2 and passing through the optical splitter 3 into a first short pulse light and a second short pulse light. The first short pulse light is sent to the optical variable delay device 4 of the first optical path OP1, and the second short pulse light is sent to the optical BPF 108 of the second optical path OP2. The optical splitter 104 is made of, for example, a half mirror and splits the first short pulse light that has passed through the optical variable delay device 4 into a third short pulse light and a fourth short pulse light. The third short pulse light is sent to the optical multiplexer 105, and the fourth short pulse light is sent to the electro-optic sampling unit 30. The optical BPF 108 expands the pulse width of the second optical pulse light. The optical multiplexer 105 multiplexes the third short pulse light split by the optical splitter 104 and the optical BPF passing light that has passed through the optical BPF 108 to generate interference light. When the pulse width of the optical BPF passing light is wider than the propagation time difference due to the optical path length difference between the optical paths OP1 and OP2, interference occurs and interference light is obtained. The interference light is sent to the optical receiver 106.

[0188] The optical receiver 106 includes, for example, a low-speed photodiode, detects the intensity of the interference light, and outputs it as an interference signal. The interference signal is a sinusoidal repetitive signal that reaches a peak when the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 is equal to an integer multiple of the central wavelength (period) of the optical BPF passing light.

[0189] The frequency divider 107 divides the frequency of the interference signal output from the optical receiver 106. If the division ratio of the frequency divider 107 is N (N is an integer), then the frequency divider 107 outputs a rectangular wave in which the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 rises every N times the central wavelength (period) of the optical BPF passing light.

[0190] FIG. 16(a) is a diagram showing the relationship between the phase of the interference signal and the frequency drift of the pulse laser as the short-pulse light source 2 when an optical BPF is inserted in only one of the optical paths. The optical BPF is configured as an etalon + wavelength filter. The passband width of the optical BPF BW(BPF)=f repThe wavelength filter is a rectangle with a width of 100 GHz. The relationship between the phase of the interference signal and the frequency drift of the pulse laser shows a sine-wave curve on the graph, and is almost the same even if the delay amount L is changed.

[0191] Fig. 16(b) is a diagram showing the relationship between the delay amount L and the amplitude of the interference signal when the frequency drift of the pulse laser is set to 50 MHz under the same conditions as Fig. 16(a). The delay amount (optical path difference) L is L=c / 2f rep Even when the optical fiber is 1.5 m, the interference signals of the modes symmetric with respect to the center frequency of the optical BPF do not have equal amplitude and opposite phase, and the interference signal does not become zero.

[0192] The interferometer 110B of this embodiment is configured such that the optical BPF 108 is inserted into only one of the first optical path OP1 and the second optical path OP2. In the interferometer 110B, the impulse response of the optical BPF 108 is not inversion symmetric with respect to time, so the interference signal is not positive-negative symmetric with respect to zero optical path length difference. Therefore, the delay amount (optical path difference) L is L=c / 2f rep Even when the delay is 0 m or 3 m (c / f = 1.5 m), the interference signal does not become zero, so it is possible to correct an optical variable delay device with a long delay. The time response of the optical BPF 108 is asymmetric, and the transmitted light has a large delay component, so it is desirable to install the optical BPF 108 on the side with a shorter optical path length. rep ) the phase changes suddenly by 90 degrees (when the frequency drift is ±25 MHz), so it is desirable to avoid this.

[0193] <Variation 3> Another example of the configuration of the interferometer will be described with reference to FIG.

[0194] The interferometer 110C in FIG. 17 includes an optical splitter 103 provided at the branching point of the first optical path OP1 and the second optical path OP2, an optical splitter 104 provided on the first optical path OP1 on the opposite side of the optical splitter 103 across the optical variable delay device 4, a first optical BPF 108A provided downstream of the optical splitter 104 on the first optical path OP1, a second optical BPF 108B provided on the second optical path OP2, and an optical multiplexer 105 provided at the joining point of the first optical path OP1 and the second optical path OP2.

[0195] The interferometer 110C inputs short pulse light to a first optical path OP1 including an optical variable delay device 4 and a second optical path OP2 not including an optical variable delay device 4, and causes interference between a first optical BPF passing light output from a first optical BPF 108A provided in the first optical path OP1 and a second optical BPF passing light output from a second optical BPF 108B provided in the second optical path OP2, and outputs the interference light.

[0196] Specifically, the optical splitter 103 is made of, for example, a half mirror and splits the short pulse light output from the short pulse light source 2 and passed through the optical splitter 3 into a first short pulse light and a second short pulse light. The first short pulse light is sent to the variable optical delay device 4 of the first optical path OP1, and the second short pulse light is sent to the second optical BPF 108B of the second optical path OP2. The optical splitter 104 is made of, for example, a half mirror and splits the first short pulse light that has passed through the variable optical delay device 4 into a third short pulse light and a fourth short pulse light. The third short pulse light is sent to the optical multiplexer 105 via the first optical BPF 108A, and the fourth short pulse light is sent to the electro-optic sampling unit 30. The optical multiplexer 105 multiplexes the first optical BPF passing light that has passed through the first optical BPF 108A and the second optical BPF passing light that has passed through the second optical BPF 108B to generate interference light. The interference light is sent to the optical receiver 106.

[0197] The photoreceiver 106 includes, for example, a low-speed photodiode, detects the intensity of the interference light, and outputs it as an interference signal. The interference signal is a sinusoidal repetitive signal that reaches a peak when the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 is equal to an integer multiple of the central wavelength (period) of the interference light.

[0198] The frequency divider 107 divides the frequency of the interference signal output from the photoreceiver 106. If the division ratio of the frequency divider 107 is N (N is an integer), then the frequency divider 107 outputs a rectangular wave in which the optical path length difference (delay time) between the first optical path OP1 and the second optical path OP2 rises every N times the central wavelength (period) of the interference light.

[0199] The interferometer 110C of this embodiment is a type in which the optical BPF is split into two and installed in both optical paths. For example, the optical BPF 108A may be an etalon and the optical BPF 108B may be a wavelength filter, or vice versa. Alternatively, the first optical BPF 108A may be a first etalon and the second optical BPF 108B may be a second etalon having a different FSR (i.e., resonator length) from the first etalon.

[0200] <Modification 4> Another example of the configuration of the interferometer will be described with reference to FIG.

[0201] Interferometer 110D in Fig. 18 differs from Modification 2 shown in Fig. 15 in that optical multiplexer 105 is optical multiplexer / demultiplexer 105B, and optical receiver 106 is differential optical receiver 106A. The other configurations are the same as in Modification 2, and the same configurations are denoted by the same reference numerals and detailed descriptions are omitted as appropriate.

[0202] The optical multiplexer / demultiplexer 105B receives the third short pulse light demultiplexed from the optical demultiplexer 104, reflects a predetermined ratio of the input light, and transmits a predetermined ratio of the input light, and also receives the optical BPF-passing light sent from the optical BPF 108, reflects a predetermined ratio of the input light, and transmits a predetermined ratio of the input light. The transmitted third short pulse light and the reflected optical BPF-passing light are multiplexed to generate a first interference light IL1. The reflected third short pulse light and the transmitted optical BPF-passing light are multiplexed to generate a second interference light IL2. The first interference light IL1 and the second interference light IL2 are reflected and transmitted in the optical multiplexer / demultiplexer 105B inversely, so that they are complementary interferences. The differential photoreceiver 106A receives the first interference light IL1 and the second interference light IL2, differentially detects the intensities of the interference lights, and outputs them as an interference signal. The frequency divider 107 divides the interference signal to an appropriate frequency.

[0203] With this configuration, the phase characteristic calibration device according to this embodiment has twice the amplitude of the interference signal (S / N is √2 times) compared to the second modification of Fig. 15, and by detecting the zero crossing point, it is possible to extract phase information without being affected by amplitude fluctuations. Therefore, in addition to the effects of the second modification of Fig. 15, it is possible to remove in-phase noise, increase the intensity of the interference signal, and improve the S / N ratio.

[0204] <Variation 5> Another example of the configuration of the interferometer will be described with reference to FIG.

[0205] Interferometer 110E in Fig. 19 differs from Modification 3 shown in Fig. 17 in that optical multiplexer 105 is optical multiplexer / demultiplexer 105B, and optical receiver 106 is differential optical receiver 106A. The other configurations are the same as in Modification 3, and the same configurations are denoted by the same reference numerals and detailed descriptions are omitted as appropriate.

[0206] The optical multiplexer / demultiplexer 105B receives the first optical BPF passing light sent from the first optical BPF 108A, reflects a predetermined ratio of the input light, and transmits a predetermined ratio of the input light, and receives the second optical BPF passing light sent from the second optical BPF 108B, reflects a predetermined ratio of the input light, and transmits a predetermined ratio of the input light. The transmitted first optical BPF passing light and the reflected second optical BPF passing light are multiplexed to generate a first interference light IL1. The reflected first optical BPF passing light and the transmitted second optical BPF passing light are multiplexed to generate a second interference light IL2. The first interference light IL1 and the second interference light IL2 are reflected and transmitted in the optical multiplexer / demultiplexer 105B in the opposite directions, so that they are complementary interferences. The differential photoreceiver 106A receives the first interference light IL1 and the second interference light IL2, differentially detects the intensities of the interference lights, and outputs them as an interference signal. The frequency divider 107 divides the interference signal to an appropriate frequency.

[0207] With this configuration, the phase characteristic calibration device according to this embodiment has twice the amplitude of the interference signal (S / N is √2 times) compared to the third modification in Fig. 17, and by detecting the zero crossing point, it is possible to extract phase information without being affected by amplitude fluctuations. Therefore, in addition to the effects of the third modification in Fig. 17, it is possible to remove in-phase noise, increase the intensity of the interference signal, and improve the S / N ratio.

[0208] Moreover, the interferometers of the above-mentioned modifications 1 to 5 can be used not only in the first embodiment but also as interferometers of the phase characteristic calibration devices of the second to eighth embodiments described later.

[0209] [Calibration method] Next, returning to FIG. 5, a method for calibrating the frequency characteristics of the frequency conversion units (down converters) 72 and 73 of the millimeter wave band signal measuring unit 70 will be described.

[0210] Here, the frequency characteristic is expressed as a complex number A·e containing amplitude A and phase θ. jθ It can be used to calibrate the frequency characteristics of both phase and amplitude. 20 The frequency characteristic (complex number) of X c(f), the frequency characteristics (complex numbers) of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 are G(f), and the calibration signal S 20 is input to the millimeter wave band signal measuring unit 70, the output signal S from the intermediate frequency signal converting unit 73 is 70 The frequency characteristic (complex number) of Y c (f). As mentioned above, the calibration signal S 20 is input to the electro-optic sampling unit 30 and measured. 20 Phase characteristic S 50 From X c (f) is obtained, and the calibration signal S 20 is input to the millimeter wave band signal measuring unit 70 and the frequency converted output signal S 70 Phase characteristic S 50' From Y c Once (f) is found, G(f) can be found using the following equation. G(f)=Y c (ff LO ) / X c (f) (3) where f LO is the local oscillator frequency of the millimeter wave band signal measuring unit 70.

[0211] The phase correction value calculation unit 55 calculates G(f) over a predetermined frequency range and outputs it to the phase correction unit 74 of the millimeter wave band signal measurement unit .

[0212] Signal under test S 60 The frequency characteristic (complex number) of X(f) and the measured signal S 60 is input to the millimeter wave band signal measuring unit 70, the output signal S from the intermediate frequency signal converting unit 73 is 70' If the frequency characteristic (complex number) of is Y(f), then X(f) in which the frequency characteristics of the frequency conversion units 72 and 73 of the millimeter waveband signal measuring unit 70 have been corrected can be found as the measurement result using the following equation. X(f)=Y(ff LO ) / G(f) (4)

[0213] The switches SW3 and SW4 are set to the lower side in FIG. 5, and the measured signal S 60is input to the millimeter wave band signal measuring unit 70, and the output signal S 70' is input to the phase correction unit 74. The phase correction unit 74 divides the signal by the frequency characteristic G(f) of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 (if only the phase is to be corrected, the phase characteristic of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 is subtracted), thereby obtaining a measurement result in which the frequency characteristics of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 have been corrected.

[0214] <Effects> The phase characteristic calibration device 1 of this embodiment can simultaneously perform electro-optic sampling and acquire an interference signal to correct unpredictable random fluctuations in the sweep speed of the variable optical delay device 4, such as mechanical "wobble," and can improve the complexity and cost-effectiveness of the optical system compared to the conventional technology (fifth configuration example) shown in FIG. 31, since the short-pulse light output from the short-pulse light source 2 and passing through the variable optical delay device 4 is used for electro-optic sampling and also for the interferometer 110, the influence of deformation due to temperature change and the like is the same for both, and the influence can be accurately corrected. For example, in a method of correcting the sweep speed by separately arranging an encoder that detects the sweep speed of the variable optical delay device 4, an error occurs between the delay time of the short-pulse light and the encoder output due to deformation due to temperature change, making it difficult to accurately correct the sweep speed of the variable optical delay device 4.

[0215] Second embodiment Next, a phase characteristic calibrating apparatus 1A according to a second embodiment of the present invention will be described with reference to FIG.

[0216] The phase characteristic calibration apparatus 1A according to this embodiment differs from that of the first embodiment in the configuration of a multi-tone signal sampling section 120A. The other configurations are the same as those of the first embodiment, and the same configurations are denoted by the same reference numerals and detailed descriptions are omitted as appropriate.

[0217] As shown in FIG. 20, multi-tone signal sampling section 120A includes an A / D converter 111 that converts the multi-tone signal output from lock-in detection section 40 into a digital signal, a low-pass filter 112 that blocks harmonic components of the rectangular wave output from frequency divider 107 and converts it into a sine wave, a second A / D converter 113 that performs A / D conversion on the output signal of low-pass filter 112, and a resampling processing section 130 that detects equal phase intervals based on a signal obtained by frequency-dividing the interference signal and resamples the digital signal output from A / D converter 111 at the detected equal phase intervals.

[0218] Specifically, the resampling processing unit 130 includes a Hilbert transform unit 114 that performs a Hilbert transform on the digital signal obtained by the second A / D converter 113, an equal phase interval detection unit 115 that detects equal phase intervals from the output data of the Hilbert transform unit 114, and a resampling unit 116 that resamples the output signal of the A / D converter 111 at the detected equal phase intervals.

[0219] When detecting the timing of equal phase intervals from a sine wave signal obtained by dividing an interference signal and passing it through a low-pass filter, the phase cannot be uniquely determined by the sine wave alone, so a Hilbert transform is performed to create a sine wave and a cosine wave and generate a complex amplitude signal. This allows the equal phase interval detection unit 115 to uniquely calculate the phase of the complex amplitude signal using an arctangent function, and to accurately detect equal phase intervals.

[0220] In the resampling method, since the sampling frequency of resampling can be changed by changing the phase interval detected by equal phase interval detection unit 115, it is not necessary to set the division ratio to an oversampling ratio r≧1. For example, if the division ratio is set so that the oversampling ratio r=1 / 2 and the frequency of the output of frequency divider 107 is approximately the same as the frequency of the multi-tone signal output from lock-in detection unit 40, the two A / D converters 111 and 113 can be operated at the same sampling frequency, simplifying the configuration. In this case, if the phase interval detected by equal phase interval detection unit 115 is set to π / 2, the resampling output will be 2x oversampling.

[0221] As described above, by using a configuration in which the multi-tone signal is resampled at equal phase intervals of the output signal of frequency divider 107, which divides the interference signal, the multi-tone signal obtained by electro-optic sampling can be resampled at constant intervals with respect to the delay amount, regardless of the sweep speed of variable optical delay device 4. This makes it possible to correct phase fluctuations in the signal obtained by electro-optic sampling that are caused by instability in the sweep speed of variable optical delay device 4.

[0222] (Third embodiment) Next, a phase characteristic calibrating apparatus 1B according to a third embodiment of the present invention will be described with reference to FIG.

[0223] A phase characteristic calibration apparatus 1B according to this embodiment differs from the first embodiment in the configurations of a calibration signal generating section 20B, a multi-tone signal separating section 40B, a multi-tone signal sampling section 120B, and a multi-tone phase difference measuring section 50B. The other configurations are the same as those of the first embodiment, and the same configurations are denoted by the same reference numerals and detailed descriptions are omitted as appropriate.

[0224] When the switch SW10 is set to the upper side in the figure, the calibration signal generating unit 20B generates a local oscillator signal S 22 Using the multi-tone intermediate frequency signal S 10 is up-converted to produce a calibration signal S 20For this purpose, the calibration signal generating section 20B includes a multi-tone intermediate frequency signal generating / reference signal modulating section 10B, a local oscillator signal generating section 22, and a frequency converting section .

[0225] The multi-tone intermediate frequency signal generating and reference signal modulating unit 10B generates multi-tone signals (intermediate frequency signals) S1 to S4 with three or more tones, modulates them with the same number of reference signals as the intermediate frequency signals (i.e., mutually orthogonal reference signals) S5 to S8, which have different frequencies or phases differing by 90 degrees from each other, and combines the modulated signals to generate a multi-tone intermediate frequency signal S 10 Specifically, the multi-tone intermediate frequency signal generating / reference signal modulating unit 10B generates intermediate frequency signals S1 to S4 having different frequencies, and modulates and combines the intermediate frequency signals with reference signals S5 and S7 having different frequencies from each other, or orthogonal reference signals S6 and S8 having the same frequency as the reference signals and a phase difference of 90 degrees, to generate a multi-tone intermediate frequency signal S 10 In this embodiment, an example of generating a four-tone signal is shown. The reference signal S5 and the reference signal S7, the reference signal S5 and the orthogonal reference signal S8, the reference signal S7 and the orthogonal reference signal S6, and the orthogonal reference signal S6 and the orthogonal reference signal S8 are orthogonal because they have different frequencies, and the reference signal S5 and the orthogonal reference signal S6, and the reference signal S7 and the orthogonal reference signal S8 are orthogonal because they have the same frequency but a phase difference of 90 degrees. Therefore, the reference signals S5, S7 and the orthogonal reference signals S6, S8 are orthogonal to each other in all combinations.

[0226] More specifically, the multi-tone intermediate frequency signal generation / reference signal modulation section 10B includes intermediate frequency signal generators 11a-11d, reference signal generators 12a, 12b, 90 degree phase shifters 14a, 14b, modulators 13a-13d, an adder 15, and a reference synchronization signal generator 16.

[0227] The intermediate frequency signal generators 11a to 11d generate intermediate frequency signals S1 to S4, respectively. The intermediate frequency signals S1 to S4 are repetitive signals having different frequencies and a predetermined phase difference. Usually, a sine wave is used, but any repetitive signal having a desired frequency component may be used. As will be described later, in order to simplify the phase measurement data processing, it is desirable to set the frequencies of the intermediate frequency signals S1 to S4 at a constant frequency interval according to the frequency resolution of the phase measurement.

[0228] The reference signal generator 12a receives a reference synchronization signal S from a reference synchronization signal generator 16. 16 The reference signal generator 12a outputs a repetitive signal having a frequency synchronized with the reference synchronization signal S5. 16 The modulator 13b outputs a sine wave or square wave having a frequency three times that of the reference signal S5. The reference signal S5 is input to the modulator 13a, which modulates the intermediate frequency signal S1 with the reference signal S5. The reference signal S5 is also input to the modulator 13b via the 90-degree phase shifter 14a, which modulates the intermediate frequency signal S2 with the orthogonal reference signal S6 that is 90 degrees out of phase with the reference signal S5.

[0229] The reference signal generator 12b has a frequency different from that of the reference signal S5 and receives the reference synchronization signal S from the reference synchronization signal generator 16. 16 The reference signal generator 12b outputs a repetitive signal having a frequency synchronized with the reference synchronization signal S7. 16 The modulator 13c outputs a sine wave or square wave having a frequency four times that of the reference signal S7. The reference signal S7 is input to the modulator 13c, which modulates the intermediate frequency signal S3 with the reference signal S7. The reference signal S7 is also input to the modulator 13d via the 90-degree phase shifter 14b, which modulates the intermediate frequency signal S4 with the orthogonal reference signal S8 that is 90 degrees out of phase with the reference signal S7.

[0230] The reference signals S5, S7 and the orthogonal reference signals S6, S8 may be unipolar signals with a voltage of zero or more or bipolar signals with both positive and negative polarities, but bipolar signals without a DC component are preferable because they can increase the modulation depth. If the reference signals S5, S7 and the orthogonal reference signals S6, S8 are repetitive signals other than sine waves, such as rectangular waves, there are harmonic components that are integer multiples of the fundamental frequency, so it is advisable to set the frequencies of both signals so that, for example, the integer multiple of the frequency of the reference signal S5 does not match the frequency of the reference signal S7.

[0231] The multi-tone intermediate frequency signal generating and reference signal modulating unit 10B adds (combines) the intermediate frequency signals modulated by the modulators 13a to 13d in an adder 15 to generate a multi-tone intermediate frequency signal S 10 The output is as follows:

[0232] The signal generated by the multi-tone intermediate frequency signal generating and reference signal modulating section 10B is generated in advance by digital calculation and stored in a waveform memory, and the data in the waveform memory is input to a D / A converter and converted into an analog signal to generate a multi-tone intermediate frequency signal S 10 It may be output as:

[0233] Here, one reference sync signal S 16 The reference signal S5 and the reference signal S7 are generated in synchronization with each other. 16A and the reference sync signal S 16B The reference signal S5 is the reference sync signal S 16A and the reference signal S7 is synchronized with the reference synchronization signal S 16B The configuration may be such that the two are synchronized with each other.

[0234] The calibration signal generating unit 20B generates a CW local oscillator signal S 22 and a frequency converter 21 such as a mixer to generate a multi-tone intermediate frequency signal S 10 is up-converted to the millimeter wave band to produce the calibration signal S 20 The frequency converter 21 extracts either the upper sideband or the lower sideband in the frequency conversion after the mixer and outputs the local oscillator signal S 22A filter to remove leakage of the signal may be included. The following example shows the case where the upper sideband is used in the frequency conversion. When the lower sideband is used, the frequency relationship is different, but the method can be applied in the same way.

[0235] The local signal generator 22 or the frequency converter 21 receives a local signal S 22 In this case, the frequency multiplier may be included to multiply the frequency of the local oscillator signal S 22 This is interpreted as the frequency of.

[0236] The synchronization processor 5 synthesizes the intermediate frequency signals S1 to S4 and the local oscillator signal S 22 and the repetition frequency of the short pulse light source 2, a millimeter wave calibration signal S synchronized with the repetition frequency of the short pulse light source 2 is generated. 20 Specifically, the synchronization processing unit 5 receives the short pulse light P3 output from the optical splitter 3 and outputs the calibration signal S 20 The intermediate frequency signals S1 to S4 and the local signal S are converted so that the frequencies of the up-converted intermediate frequency signals included in the short pulse light P3 are integer multiples of the repetition frequency of the short pulse light P3 and the phases of the up-converted intermediate frequency signals are constant at the pulse timing of the short pulse light P3. 22 The frequency of the signal is controlled by the oscilloscope.

[0237] More specifically, the synchronization processor 5 uses a phase-locked loop (PLL) circuit to synchronize the local oscillator signal S 22 The frequency of each of the intermediate frequency signals S1 to S4 is an integer multiple of the repetition frequency of the short pulse light source 2, and the local signal S 22 The local signal generating section 22 and the voltage controlled oscillators (VCOs) in the intermediate frequency signal generators 11a to 11d are controlled so that the phases of the sine waves output from the intermediate frequency signal generators 11a to 11d are constant.

[0238] In addition, the reference sync signal S 16may or may not be synchronized with the repetition frequency of the short pulse light source 2. As described above, when the multi-tone intermediate frequency signal generating / reference signal modulating section 10B is configured with a waveform memory and a D / A converter, the D / A conversion clock is synchronized with the repetition frequency of the short pulse light source 2, and the data in the waveform memory is created so that each frequency of the intermediate frequency signals in the multi-tone intermediate frequency signal is an integer multiple of the repetition frequency of the short pulse light source 2. This causes the calibration signal S (excluding the modulation by the reference signals S5, S7 and the orthogonal reference signals S6, S8) to 20 The repetition frequency of this pulse is an integer multiple of the repetition frequency of the short pulse light source 2.

[0239] The calibration signal S is obtained by using the electro-optic sampling unit 30. 20 When measuring the phase difference between the two, the switches SW1 and SW21 to SW24 are set to the upper side in FIG. 21. The electro-optic sampling unit 30 detects the calibration signal S 20 The electric field is applied to the electro-optic crystal 31, and the short pulse light P4 from the variable optical delay device 4 is input to the electro-optic crystal 31 via the polarization separator 32, and the short pulse light reflected at the tip of the electro-optic crystal 31 is input to the photoreceiver 33 via the polarization separator 32. When an electric field is applied to the electro-optic crystal 31, the polarization of the reflected light from the electro-optic crystal 31 changes due to the electro-optic effect, and the polarization change of the reflected light is detected by the polarization separator 32 and the photoreceiver 33 to produce an electrical signal S 30 The output is as follows:

[0240] The pulse width of the short pulse light P4 is the calibration signal S 20 If the frequency is made sufficiently shorter than half the reciprocal of the maximum frequency of the electrical signal S 30 is the calibration signal S 20 The repetition period of the short pulse light source 2 is the same as the repetition period of the calibration signal S (excluding the modulation by the reference signals S5 and S7 and the orthogonal reference signals S6 and S8). 20 Since the repetition period of the calibration signal S (excluding the modulation by the reference signals S5 and S7 and the orthogonal reference signals S6 and S8) is an integer multiple of 20By changing the delay time of the optical variable delay device 4, the calibration signal S 20 Since the time when the short pulse light P4 is sampled changes, the delay time of the variable optical delay device 4 is swept while the electrical signal S from the electro-optic sampling unit 30 is sampled. 30 When the signal is recorded, the millimeter-wave calibration signal S is generated by the low-speed receiver 33. 20 The time waveform can be measured.

[0241] Specifically, the electrical signal S from the electro-optic sampling unit 30 30 is the calibration signal S 20 The time axis of the time waveform of is multiplied by the sweep rate of the variable optical delay device 4. For example, if the sweep rate of the variable optical delay device 4 is set to 1 ps per 1 s, the calibration signal S 20 The time waveform can be measured by expanding the time axis from 1ps to 1s. In terms of frequency, the calibration signal S of the 300GHz millimeter wave band is 20 can be converted into a low-frequency signal of 0.3 Hz and measured.

[0242] The electrical signal S from the electro-optic sampling unit 30 30 is input to multi-tone signal separation section 40B.

[0243] The multi-tone signal separator 40B separates the calibration signal S 20 While changing the relative time difference between the electrical signal S and the short pulse light P4, 30 and a sine wave S with the same frequency and a specified phase difference as the reference signals S5 and S7 is obtained. 42 ,S 44 Or a sine wave S that is 90 degrees out of phase with the sine wave 43 ,S 45 and the electrical signal S 30 By modulating the electrical signal S 3021. To this end, multi-tone signal separation section 40B includes reference signal generators 41a-41b, phase shifters 42a-42b, 90-degree phase shifters 43a-43b, modulators 44a-44d, and low-pass filters 45a-45d. 42 and the sine wave S 44 , sine wave S 42 and the sine wave S 45 , sine wave S 44 and the sine wave S 43 , sine wave S 43 and the sine wave S 45 are orthogonal because they have different frequencies, and the sine wave S 42 and the sine wave S 43 , sine wave S 44 and the sine wave S 45 are orthogonal because they have the same frequency but a phase difference of 90 degrees. 42 ~S 45 are mutually orthogonal in all combinations.

[0244] The reference signal generator 41a receives the reference synchronization signal S from the reference synchronization signal generator 16. 17 According to the above, a reference signal S5, which is a sine wave having the same frequency as the reference signal S5, is 40 Here, the reference sync signal S 17 is usually the reference sync signal S 16 However, the present invention is not limited to this, and may be applied to, for example, a reference synchronization signal S 17 is the reference sync signal S 16 Even if the frequency is half that of the reference signal S5 and the reference signal S 40 The reference signal generator 41a may be appropriately set so that the frequencies are equal to each other.

[0245] The phase shifter 42a converts the calibration signal S sampled by the electro-optic sampling unit 30 into a phase signal S 1 , which is then input to the modulator 44a. 20 The phase of the reference signal S5 in 40 The reference signal S 40 Adjust the phase of the reference signal S 42Here, the reference signal S 40 The order of the reference signal generator 41a and the phase shifter 42a is changed to adjust the phase of the reference synchronization signal S 17 The phase of the reference signal S is adjusted by the reference signal generator 41a. 42 Alternatively, the frequency of the reference signal S5 may be low and the calibration signal S 20 and the reference sync signal S 17 If the phase difference due to the difference in propagation delay time can be ignored, the phase shifter 42a can be omitted.

[0246] The modulator 44a receives the electrical signal S from the electro-optic sampling unit 30. 30 Let S be the reference signal. 42 The output of the phase shifter 42a is input to a modulator 44b via a 90-degree phase shifter 43a, and the modulator 44b converts the electrical signal S 30 Let S be the reference signal. 42 and a reference signal S 43 and the low-frequency components are extracted by low-pass filter 45b.

[0247] The reference signal generator 41b receives the reference synchronization signal S from the reference synchronization signal generator 16. 17 According to the above, a reference signal S7, which is a sine wave having the same frequency as the reference signal S7, is 41 occurs.

[0248] The phase shifter 42b converts the calibration signal S sampled by the electro-optic sampling unit 30 into a signal S in the modulator 44c. 20 The phase of the reference signal S7 in 41 The reference signal S 41 Adjust the phase of the reference signal S 44 Here, the phase shifter 42b outputs the reference signal S 41 The order of the reference signal generator 41b and the phase shifter 42b is changed to adjust the phase of the reference synchronization signal S 17The phase of the reference signal S is adjusted by the reference signal generator 41b. 44 Alternatively, the frequency of the reference signal S7 may be low and the calibration signal S 20 and the reference sync signal S 17 If the phase difference due to the difference in propagation delay time can be ignored, the phase shifter 42b can be omitted.

[0249] The modulator 44c receives the electrical signal S from the electro-optic sampling unit 30. 30 Let S be the reference signal. 44 The output of the phase shifter 42b is input to a modulator 44d via a 90-degree phase shifter 43b, and the modulator 44d converts the electrical signal S 30 Let S be the reference signal. 44 and a reference signal S 45 and the low-frequency components are extracted by a low-pass filter 45d.

[0250] Here, the reference sync signal S 16 ,S 17 According to the above, the reference signal S5, the reference signal S7, and the reference signal S 40 and the reference signal S 41 However, a reference signal generator A and a reference signal generator B that generate sine waves with different frequencies are prepared, and the output signal of the reference signal generator A is the reference signal S5 and the reference signal S 40 and the output signal of the reference signal generator B is used as the reference signal S7 and the reference signal S 41 It may be configured to be used as such.

[0251] With the above configuration, the electrical signal S 30 The four tones are separated.

[0252] In the following, the calibration signal S 20 The angular frequencies of the four tones are expressed as ω RF1 ,ω RF2 ,ω RF3 ,ω RF4 , each phase is φ1, φ2, φ3, φ4, reference signal S40 The angular frequency of ω r1 , reference signal S 41 The angular frequency of ω r2 , the sweep rate of the optical variable delay device 4 is R.

[0253] In general, the low-pass filters 45a to 45d are r1 -ω r2 The electric signal S from the electro-optic sampling unit 30 is 30 The angular frequency of the four-tone signal at Rω RF1 ,Rω RF3 ,Rω RF2 ,Rω RF4 By setting the cutoff frequency to pass the tones, it is possible to separate the tones. If the cutoff frequency of the low-pass filters 45a to 45d is lowered, the sweep speed of the variable optical delay 4 must be slowed down, and measurement takes time, but the measurement frequency band is narrowed and the signal-to-noise ratio is improved.

[0254] In addition, the phase detection sections 51a-51d of the subsequent multi-tone phase difference measurement section 50B generally have frequency selectivity for detecting the frequencies of each of the four tones, and it is easy to set the measurement band of the phase detection sections 51a-51d narrower than the band of the low-pass filters 45a-45d of the multi-tone signal separation section 40B. In this case, since the S / N ratio of the phase measurement is determined by the latter, the low-pass filters 45a-45d of the multi-tone signal separation section 40B may be set to a cutoff frequency appropriate for use as an anti-aliasing filter when A / D conversion is performed before the multi-tone phase difference measurement section 50B as in this embodiment, or when the sampling rate is lowered to reduce the amount of calculation in the phase detection sections 51a-51d.

[0255] In addition, the electrical signal S from the electro-optic sampling unit 30 30 In the case of the sampled four-tone signal, the angular frequency Rω RF1 ,Rω RF3 ,Rω RF2 ,Rω RF4 Instead, the angular frequency ω modulated by the reference signal S5 and the reference signal S7 is r1 ±Rω RF1 ,ωr1 ±Rω RF3 ,ω r2 ±Rω RF2 ,ω r2 ±Rω RF4 To detect the components of, for example, ω r1 and ω r2 to several MHz, a signal with a frequency of several MHz can be measured, making it possible to avoid DC drift and 1 / f noise in the photoreceiver 33 of the electro-optic sampling unit 30 and perform measurements with a high S / N ratio. In this way, the multi-tone signal separation unit 40B of this embodiment has both the function of lock-in detection and the function of separating multi-tone signals, enabling measurements with good sensitivity.

[0256] Since each tone signal is separated in the multi-tone signal separation unit 40B, it is also possible to arrange each tone signal at a frequency interval narrower than the frequency resolution Δf=1 / T determined by the sweep width T of the variable optical delay device 4. This makes it possible to measure the phase characteristics with a narrow frequency interval without increasing the size of the variable optical delay device 4.

[0257] In addition, the calibration signal S 20 Even if there is phase fluctuation in the calibration signal S, it is possible to prevent leakage of adjacent tone signals and perform accurate phase measurement. 20 To generate the local oscillator signal S 22 This is useful because the phase fluctuation of

[0258] In addition, electrical components such as high-frequency mixers and amplifiers generally have nonlinear distortion, and when two sine waves with different frequencies are input, new spectra are generated on both sides of the spectrum of the two input sine waves due to third-order intermodulation distortion. 20 The frequencies of the first, second, third, and fourth tones are f RF1 ,f RF2 ,f RF3 ,f RF4 , the reference signal S5 is at frequency f r1 A sine wave of reference signal S7 with frequency f r2sine wave, modulation of each tone by reference signal S5 or reference signal S7 produces an upper sideband and a lower sideband.

[0259] This calibration signal S 20 When this is input to a third-order nonlinear element, the third-order intermodulation between the lower sideband of the first tone and the upper sideband of the first tone results in f RF1 From 3F r1 A spectrum is generated at distant frequencies, and the third-order intermodulation between the lower sideband of the first tone and the upper sideband of the second tone produces f RF3 2F from r2 +f r1 A spectrum is generated at distant frequencies, and the third-order intermodulation between the upper sideband of the first tone and the upper sideband of the second tone produces f RF3 2F from r2 -f r1 Similarly, the calibration signal S 20 A spectrum of third-order intermodulation distortion occurs around the first to fourth tones.

[0260] In this way, a total of 24 spectra due to third-order intermodulation distortion are generated near the first to fourth tones, but do not overlap with either the upper sideband or the lower sideband of the first to fourth tones. r2 - 2nd floor r1 If it is set narrower than |, the spectrum due to third-order intermodulation distortion will be outside the band of low-pass filters 45a to 45d of multi-tone signal separation unit 40B or outside the measurement band of phase detection units 51a to 51d. Therefore, accurate phase measurement is possible without being affected by third-order intermodulation distortion.

[0261] The phase detector 51a of the multi-tone phase difference measuring unit 50B detects the electrical signal S 30 The first tone of the four tones in RF1 ) to detect the phase.

[0262] Phase detection section 51a is implemented by digital calculations that input the corrected multi-tone signal obtained by A / D converter 111a of multi-tone signal sampling section 120B, multiply it by a sine function and a cosine function, integrate the two multiplication results a predetermined number of samples, and calculate the phase using the arctangent function. Alternatively, phase detection section 51a may input the corrected multi-tone signal obtained by A / D converter 111a of multi-tone signal sampling section 120B, store it in memory, and use a CPU to multiply it by a sine function and a cosine function offline, integrate the results a predetermined number of samples, and calculate the phase using the arctangent function.

[0263] Similarly, the phase detectors 51c, 51b, and 51d detect the electrical signal S 30 The second, third and fourth tones (frequency: Rf RF2 ,Rf RF3 ,Rf RF4 The phase calculation result using the arctangent function may be corrected so as to correct the phase differences of the intermediate frequency signals S1 to S4 generated by the intermediate frequency signal generators 11a to 11d.

[0264] Generally, in phase measurement of a high-frequency signal, the absolute phase and frequency slope of the phase are indefinite, so the phase difference calculation unit 52 calculates the second derivative of each phase of the four tones and outputs it as the phase difference measurement result by the electro-optic sampling unit 30. The phases of three tones are required to calculate the second derivative, and the second derivative of the phase at two frequencies is obtained from the phase of the four tones. In the same manner, the second derivative of the phase at the frequency of N-2 points can be obtained from the phase of N tones, so this method can be extended to any number of tones greater than or equal to three.

[0265] This process is used as the calibration signal S 20 The frequency of these four tones is changed and repeated to measure the second-order differential value of the phase over a predetermined frequency range. The frequency characteristic of the phase can be obtained by integrating the second-order differential of the phase twice. In this manner, the phase difference measurement result S 50 is output from the phase difference calculation unit 52.

[0266] The calibration signal S is measured using the millimeter wave band signal measuring unit 70. 20 21, and switches SW3 and SW4 are set to the upper side of the figure. The multi-tone intermediate frequency signal generating section 25 includes intermediate frequency signal generators 26a to 26d and an adder 27, and adds intermediate frequency signals S 11 ~S 14 The multi-tone intermediate frequency signal S 15 It outputs a multi-tone intermediate frequency signal S 15 is sent to the frequency conversion unit 21 via the switch SW10, and a millimeter-wave calibration signal S 20 The calibration signal S 20 is input to the millimeter wave band signal measuring unit 70 via the switches SW1 and SW3.

[0267] The intermediate frequency signal converter 73 may include a second frequency converter that converts the frequency of the intermediate frequency signal output from the frequency converter 72 again, or an orthogonal frequency converter that converts the intermediate frequency (IF) signal into an in-phase (I) signal and a quadrature (Q) signal. When the intermediate frequency signal converter 73 includes a frequency converter, the local oscillator signal S 71 The local frequency of the intermediate frequency signal conversion unit 73 in addition to the frequency of the intermediate frequency signal conversion unit 72 is interpreted as the local frequency of the millimeter wave band signal measurement unit 70. The frequency conversion unit 72 of this embodiment and the intermediate frequency signal conversion unit 73 in the case where frequency conversion is included correspond to the downconverter of the present invention. The intermediate frequency signal conversion unit 73 also includes an A / D converter that converts the intermediate frequency signal or the I / Q signal into a digital signal, and outputs the digital signal to the multi-tone phase difference measurement unit 50B or the phase correction unit 74.

[0268] The output signal S from the intermediate frequency signal conversion unit 73 of the millimeter wave band signal measurement unit 70 70are input to phase detection units 51a to 51d of multi-tone phase difference measurement unit 50B via switches SW21 to 24. The phases of the four tones are detected in phase detection units 51a to 51d of multi-tone phase difference measurement unit 50B, and second-order differentials of the phases of the four tones are calculated in phase difference calculation unit 52, and a calibration signal S 20 The frequency of the four tones is changed and the measurement of the second-order differential value of the phase is repeated. The second-order differential of the phase is integrated twice to obtain the frequency characteristic of the phase. 50' will be output as:

[0269] In the phase detection units 51a to 51d, the intermediate frequency signals S generated by the intermediate frequency signal generators 26a to 26d are 11 ~S 14 The phase difference may be corrected.

[0270] [Calibration method] Next, a method for calibrating the frequency characteristics of the frequency conversion units (down converters) 72 and 73 of the millimeter wave band signal measuring unit 70 will be described with reference to FIG. Here, the frequency characteristic is expressed as a complex number A·e containing amplitude A and phase θ. jθ and can be applied to both the calibration of the phase frequency characteristic and the calibration of both the amplitude and phase frequency characteristics.

[0271] The amplitude frequency characteristic is A·e jθ The real part of the function is x and the imaginary part is y, and the arctangent function tan ―1 Absolute value (x) instead of (y / x) 2 +y 2 ) 1 / 2 It may be calculated, or it may be measured by a spectrum analyzer separate from the phase characteristic calibration apparatus 1B, or it may be measured by a power meter separate from the phase characteristic calibration apparatus 1B using a CW signal.

[0272] Calibration signal S 20 is input to the electro-optic sampling unit 30, the electrical signal S from the photodetector 33 is 30 The frequency characteristic (complex number) of X c (fEO ), calibration signal S 20 is input to the millimeter wave band signal measuring unit 70, the output signal S from the intermediate frequency signal converting unit 73 is 70 The frequency characteristic (complex number) of Y c (f IF ), and the frequency characteristic (complex number) of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 is G(f RF ), where f EO is the electrical signal S sampled by the electro-optic sampling unit 30. 30 The frequency of IF is the signal S 70 The frequency of RF is the calibration signal S 20 and millimeter wave signal S 60 is the frequency.

[0273] As described above, the switches SW10, SW1, SW21, SW22, SW23, and SW24 in FIG. 21 are set to the upper side in the same figure, and the calibration signal S 20 is input to the electro-optic sampling unit 30, and X is calculated from the phase measured by the multi-tone phase difference measurement unit 50B. c (f EO In addition, the switches SW10, SW1, SW21, SW22, SW23, and SW24 are set to the lower side in the figure, and the switches SW3 and SW4 are set to the upper side in the figure, and the calibration signal S 20 is input to the millimeter wave band signal measuring unit 70, and Y is calculated from the phase measured by the multi-tone phase difference measuring unit 50B. c (f IF ) is obtained. Then, from the following equation, G(f RF ) can be obtained. G(f RF )=Y c (f RF -f LO ) / X c (R f RF ) (5)

[0274] where f LOis the local frequency of the millimeter wave band signal measuring unit 70, and R is the sweep rate (the amount of change in delay time per unit time) of the optical variable delay unit 4. The phase correction value calculation unit 55 calculates G(f RF ) and outputs it to the phase correction unit 74 of the millimeter wave band signal measuring unit 70.

[0275] Signal under test S 60 The frequency characteristic (complex number) of X(f RF ), switches SW3 and SW4 are set to the lower position in the figure to measure the signal S 60 is input to the millimeter wave band signal measuring unit 70, the output signal S from the intermediate frequency signal converting unit 73 is 70' The frequency characteristic (complex number) of Y(f IF ), the phase characteristics of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 are corrected as follows: X(f RF ) can be obtained. X(f RF )=Y(f RF -f LO ) / G(f RF ) (6)

[0276] Therefore, the output signal S from the intermediate frequency signal conversion unit 73 of the millimeter wave band signal measurement unit 70 70' For the millimeter wave signal measuring unit 70, the local frequency f LO The frequency characteristic G(f RF ) in the phase correction unit 74, it becomes possible to correct the frequency characteristics of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70.

[0277] For example, the inverse H(f IF )=1 / G(f IF +f LO) to calculate a time domain impulse response at the intermediate frequency of the millimeter wave band signal measuring unit 70, and an FIR digital filter with the impulse response as a coefficient is configured in the phase correction unit 74, thereby making it possible to correct the intermediate frequency signal of the millimeter wave band signal measuring unit 70 in the time domain. When the intermediate frequency signal converting unit 73 of the millimeter wave band signal measuring unit 70 performs orthogonal frequency conversion of the intermediate frequency (IF) signal into an in-phase (I) signal and a quadrature (Q) signal, it is sufficient to calculate a complex impulse response and use a complex FIR digital filter.

[0278] The millimeter wave band signal transmitting section 60 is composed of, for example, an intermediate frequency signal generating section 61, a local signal generating section 62, and a frequency converting section 63. When the switches SW3 and SW4 in FIG. 21 are set to the lower side, the signal S to be measured from the millimeter wave band signal transmitting section 60 is 60 is input to the millimeter wave band signal measuring unit 70, and the output signal S 70' to the phase correction unit 74, it is possible to obtain a measurement result in which the frequency characteristics of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 have been corrected. The millimeter wave band signal measurement unit 70 may include, after the phase correction unit 74, a signal analyzer function that analyzes the modulated signal and displays error vector magnitude (EVM) and the like.

[0279] (Fourth embodiment) Next, a phase characteristic calibrating apparatus 1C according to a fourth embodiment of the present invention will be described with reference to FIG.

[0280] A phase characteristic calibration apparatus 1C according to this embodiment differs from that of the third embodiment in the configuration of a multi-tone signal sampling unit 120C. The other configurations are the same as those of the third embodiment, and the same configurations are denoted by the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0281] Specifically, as shown in FIG. 22, multi-tone signal sampling unit 120C includes A / D converters 111a, 111b, 111c, and 111d that convert the tone signals separated by multi-tone signal separation unit 40B into digital signals, low-pass filter 112 that blocks harmonic components of the rectangular wave output from frequency divider 107 and converts it into a sine wave, a second A / D converter 113 that performs A / D conversion on the output signal of low-pass filter 112, and resampling processing unit 130C that detects equal phase intervals based on a signal obtained by frequency-dividing the interference signal, and resamples the digital signals obtained by A / D converters 111a, 111b, 111c, and 111d at the detected equal phase intervals.

[0282] Specifically, the resampling processing unit 130C includes a Hilbert transform unit 114 that performs a Hilbert transform on the digital signal obtained by the second A / D converter 113, an equal phase interval detection unit 115 that detects equal phase intervals from the output data of the Hilbert transform unit 114, and resampling units 116a, 116b, 116c, and 116d that resample the output signals of the A / D converters 111a, 111b, 111c, and 111d, respectively, at the detected equal phase intervals.

[0283] With the above configuration, by resampling each tone signal at equal phase intervals of the output signal of the frequency divider 107 that divides the interference signal, each tone signal obtained by the electro-optic sampling unit 30 and the multi-tone signal separation unit 40B can be sampled at a constant interval with respect to the delay amount regardless of the sweep speed of the variable optical delay unit 4. This makes it possible to correct phase fluctuations in the signal obtained by electro-optic sampling, which are caused by instability in the sweep speed of the variable optical delay unit 4. Also, as in the second embodiment, it is not necessary to set the frequency division ratio to satisfy the oversampling ratio r≧1, and it is also possible to set the frequency division ratio so that the A / D converters 111a to 111d and 113 operate at the same sampling frequency.

[0284] Fifth embodiment Next, a phase characteristic calibration apparatus 1D according to a fifth embodiment of the present invention will be described with reference to FIG.

[0285] The phase characteristic calibration device 1D according to this embodiment receives a measurement intermediate frequency signal S 81 is frequency converted (up-converted) to produce the measurement signal S 80' The frequency characteristic of the phase of the frequency converter 84 of the millimeter wave band signal generator 80 is corrected, and the multi-tone intermediate frequency signal S 19 is up-converted by the local signal generator 83 and the frequency converter 84 of the millimeter wave band signal generator 80 to produce a millimeter wave band signal S 80 The second embodiment differs from the first embodiment in that the second embodiment generates the millimeter waveband signal S. The other configurations are the same as those of the first embodiment, and the same configurations are denoted by the same reference numerals and detailed descriptions thereof will be omitted as appropriate. 80 The millimeter waveband signal generating section 80 and the frequency converting section 84 correspond to the calibration signal, the signal generating section and the up-converter of the present invention, respectively.

[0286] As shown in FIG. 23, the three-tone intermediate frequency signal generating section 10 multiplexes three or more intermediate frequency signals S1, S2, and S3 having different frequencies to generate a three-tone intermediate frequency signal S 10 The reference signal modulation unit 17 outputs a three-tone intermediate frequency signal S 10 Let S be the reference signal. 18 A multi-tone intermediate frequency signal S modulated by 19 When the switches SW6 and SW7 are set to the upper side in the figure, the millimeter wave band signal generating unit 80 outputs a local oscillator signal S 83 Using the multi-tone intermediate frequency signal S 19 is up-converted by the up-converter 84 of the millimeter wave band signal generating unit 80 to generate a millimeter wave band signal S 80 Then, the millimeter wave signal S 80 is input to the electro-optic sampling section 30.

[0287] Next, a method for calibrating the phase frequency characteristics of the frequency conversion section 84 of the millimeter waveband signal generating section 80 will be described.

[0288] In the configuration shown in FIG. 23, the multi-tone intermediate frequency signal S output from the reference signal modulation section 17 19 The frequency characteristic (complex number) of X c1 (f IF1 ), and the frequency characteristic (complex number) of the frequency conversion unit 84 of the millimeter waveband signal generation unit 80 is G1(f RF ), the millimeter wave band signal S output from the frequency conversion unit 84 of the millimeter wave band signal generating unit 80 80 is input to the electro-optic sampling unit 30, the electrical signal S from the photodetector 33 is 30 The frequency characteristic (complex number) of Y c1 (f EO ), where f IF1 is the multi-tone intermediate frequency signal S 19 Frequency (intermediate frequency), f RF is the millimeter wave signal S 80 and the measurement signal S 80' The frequency of EO is the electrical signal S sampled by the electro-optic sampling unit 30. 30 is the frequency.

[0289] X c1 (f IF1 ) is a multi-tone intermediate frequency signal S generated by the three-tone intermediate frequency signal generating section 10 and the reference signal modulating section 17. 19 23. Since the frequency characteristics are known, the switches SW6 and SW7 are set to the upper side in FIG. 23, and the millimeter wave band signal S output from the frequency conversion unit 84 of the millimeter wave band signal generation unit 80 is 80 is input to the electro-optic sampling unit 30, and Y is calculated from the phase measured by the three-tone phase difference measurement unit 50. c1 (f EO ) is obtained, and G1(f RF ) can be obtained. G1(f RF )=Y c1 (R f RF ) / X c1 (f RF -f LO1 ) (7) where f LO1 is the local signal S of the millimeter wave band signal generator 80. 83is the frequency, and R is the sweep rate of the variable optical delay device 4 (the amount of change in delay time per unit time).

[0290] The phase correction value calculation unit 55 calculates G1(f RF ) is calculated. There are two methods for correcting the frequency characteristics of the frequency conversion unit 84: a method in which the frequency characteristics are corrected in the phase correction unit 82 of the millimeter wave band signal generation unit 80, and a method in which a phase correction unit is disposed after the intermediate frequency signal conversion unit 93 of the millimeter wave band signal reception unit 90 to correct the frequency characteristics. Fig. 23 shows the former case.

[0291] In the former case, the inverse H1(f IF1 )=1 / G1(f IF1 +f LO1 ) is subjected to an inverse Fourier transform to calculate the time domain impulse response at the intermediate frequency of the millimeter waveband signal generating unit 80, and an FIR digital filter using the impulse response as a coefficient is applied to the signal from the intermediate frequency signal generating unit 81 of the millimeter waveband signal generating unit 80.

[0292] In the latter case, the inverse H2(f IF2 )=1 / G1(f IF2 +f LO2 ) is inversely Fourier transformed to calculate the time domain impulse response at the intermediate frequency of the millimeter wave band signal receiving unit 90, and an FIR digital filter using the impulse response as a coefficient is applied to the signal from the intermediate frequency signal converting unit 93 of the millimeter wave band signal receiving unit 90. IF2 is the intermediate frequency signal S of the millimeter wave band signal receiving unit 90. 90 The frequency of LO2 is the local signal S of the millimeter wave band signal receiver 90 91 The millimeter wave band signal receiving unit 90 is composed of, for example, a local signal generating unit 91, a frequency converting unit 92, and an intermediate frequency signal converting unit 93. When the intermediate frequency signal converting unit 93 of the millimeter wave band signal receiving unit 90 includes frequency conversion, the frequency f LO2 is the local signal S 91This is interpreted as including the local frequency of the intermediate frequency signal conversion unit 93 in addition to the above frequency.

[0293] Switches SW6 and SW7 are set to the lower side in FIG. 23, and an arbitrary intermediate frequency signal S output from intermediate frequency signal generating section 81 of millimeter wave band signal generating section 80 is 81 is input to a phase correction unit 82 for phase correction, and is up-converted by a local signal generation unit 83 and a frequency conversion unit 84 to generate a millimeter wave band measurement signal S 80' is generated and input to the millimeter waveband signal receiving unit 90, thereby obtaining a measurement signal S in which the frequency characteristics of the frequency conversion unit 84 have been corrected. 80' Alternatively, an arbitrary intermediate frequency signal S output from the intermediate frequency signal generating section 81 of the millimeter wave band signal generating section 80 can be obtained. 81 The local signal generator 83 and the frequency converter 84 up-convert the signal to generate a measurement signal with no phase correction, which is input to the millimeter wave band signal receiver 90. The signal output from the intermediate frequency signal converter 93 is subjected to phase correction, and the measurement signal S 80' It is possible to obtain a result equivalent to that obtained when the signal is received by the millimeter waveband signal receiving unit 90 to be measured.

[0294] The intermediate frequency signal S generated by the intermediate frequency signal generating section 81 of the millimeter wave band signal generating section 80 81 may be a modulated signal such as QPSK, and the modulated signal output from the millimeter waveband signal receiving unit 90 may be analyzed to display error vector magnitude (EVM) or the like.

[0295] Sixth embodiment Next, a phase characteristic calibrating apparatus 1E according to a sixth embodiment of the present invention will be described with reference to FIG.

[0296] A phase characteristic calibration apparatus 1E according to this embodiment differs from that of the fifth embodiment in the configurations of a multi-tone intermediate frequency signal generating / reference signal modulating section 10B, a multi-tone signal separating section 40B, a multi-tone signal sampling section 120B, and a multi-tone phase difference measuring section 50B. The other configurations are the same as those of the fifth embodiment, and the same configurations are denoted by the same reference numerals and detailed explanations will be omitted as appropriate.

[0297] Specifically, as shown in FIG. 24, the multi-tone intermediate frequency signal generating / reference signal modulating unit 10B modulates three or more intermediate frequency signals S1, S2, S3, and S4 having different frequencies with the same number of mutually orthogonal reference signals S5, S6, S7, and S8 as the intermediate frequency signals, and generates a multi-tone intermediate frequency signal S 10 When the switches SW6 and SW7 are set to the upper side in the figure, the millimeter wave band signal generating unit 80 outputs a local oscillator signal S 83 Using the multi-tone intermediate frequency signal S 10 is up-converted by the up-converter 84 of the millimeter wave band signal generating unit 80 to generate a millimeter wave band signal S 80 Then, the millimeter wave signal S 80 is input to the electro-optic sampling section 30.

[0298] The configurations of multi-tone signal separating section 40B, multi-tone signal sampling section 120B, and multi-tone phase difference measuring section 50B are the same as those in the third embodiment. In addition, the method of calibrating the phase characteristics of up-converter 84 of millimeter waveband signal generating section 80 is the same as that in the fifth embodiment.

[0299] With the above-described configuration, the phase characteristic calibration device 1E according to the present embodiment uses the calibration signal S to correct the frequency characteristic of the phase of the up-converter of the millimeter wave band signal generating unit 80 that up-converts the measurement intermediate frequency signal and outputs it as a measurement signal. 80is input to electro-optic sampling unit 30, separated into individual tone signals by multi-tone signal separation unit 40B, and their phases measured by multi-tone phase difference measurement unit 50B. Since each tone signal is sampled in accordance with a signal obtained by dividing the frequency of the interference signal, fluctuations in the phase of each tone signal caused by instability in the sweep speed of variable optical delay unit 4 and the like can be reduced, thereby improving the S / N ratio.

[0300] Seventh embodiment Next, a phase characteristic calibration apparatus 1F according to a seventh embodiment of the present invention will be described with reference to Fig. 25. In the phase characteristic calibration apparatus 1F according to this embodiment, the configuration of a multi-tone signal sampling section 120A is different from that of the fifth embodiment (Fig. 23), but the other configurations are the same as those of the fifth embodiment. The same configurations are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0301] The configuration of multi-tone signal sampling unit 120A is the same as that of the second embodiment (FIG. 20). As shown in FIG. 25, multi-tone signal sampling unit 120A includes an A / D converter 111 that converts the multi-tone signal output from lock-in detection unit 40 into a digital signal, a low-pass filter 112 that blocks harmonic components of the rectangular wave output from frequency divider 107 and converts it into a sine wave, a second A / D converter 113 that performs A / D conversion on the output signal of low-pass filter 112, and a resampling processing unit 130 that detects equal phase intervals based on a signal obtained by frequency-dividing the interference signal and resamples the digital signal output from A / D converter 111 at the detected equal phase intervals.

[0302] Moreover, the method of calibrating the phase characteristics of the up-converter 84 of the millimeter waveband signal generating section 80 is the same as the calibration method described in the fifth embodiment, and therefore a description thereof will be omitted.

[0303] With the above-described configuration, the phase characteristic calibration device 1F according to the seventh embodiment uses a millimeter waveband signal S as a calibration signal in order to correct the frequency characteristic of the phase of the up-converter of the millimeter waveband signal generating unit 80 that up-converts a measurement intermediate frequency signal and outputs it as a measurement signal.80 is input to the electro-optic sampling unit 30, the multi-tone signal is detected by the lock-in detection unit 40, and the phase is measured by the three-tone phase difference measurement unit 50. Since each tone signal is resampled according to a signal obtained by dividing the frequency of the interference signal, it is possible to reduce fluctuations in the phase of each tone signal caused by instability in the sweep speed of the optical variable delay unit 4, etc., and improve the S / N ratio, thereby improving the accuracy of the phase characteristic calibration.

[0304] Eighth embodiment Next, a phase characteristic calibration device 1G according to an eighth embodiment of the present invention will be described with reference to Fig. 26. In the phase characteristic calibration device 1G according to this embodiment, the configuration of a multi-tone signal sampling unit 120C is different from that of the sixth embodiment (Fig. 24), but the other configurations are the same as those of the sixth embodiment. The same configurations are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0305] The configuration of multi-tone signal sampling unit 120C is the same as that of the fourth embodiment (FIG. 22). As shown in FIG. 26, multi-tone signal sampling unit 120C includes A / D converters 111a, 111b, 111c, and 111d that convert each tone signal separated by multi-tone signal separation unit 40B into a digital signal, low-pass filter 112 that blocks harmonic components of the rectangular wave output from frequency divider 107 and converts it to a sine wave, a second A / D converter 113 that performs A / D conversion on the output signal of low-pass filter 112, and resampling processing unit 130C that detects equal phase intervals based on a signal obtained by frequency-dividing the interference signal, and resamples the digital signals obtained by A / D converters 111a, 111b, 111c, and 111d at the detected equal phase intervals.

[0306] The method of calibrating the phase characteristics of the up-converter 84 of the millimeter waveband signal generating section 80 is the same as the calibration method described in the sixth embodiment, and therefore a description thereof will be omitted.

[0307] With the above-described configuration, the phase characteristic calibration device 1G according to the eighth embodiment uses a millimeter waveband signal S as a calibration signal in order to correct the frequency characteristic of the phase of the up-converter of the millimeter waveband signal generating unit 80 that up-converts a measurement intermediate frequency signal and outputs it as a measurement signal. 80 is input to the electro-optic sampling unit 30, separated into individual tone signals by the multi-tone signal separation unit 40B, and the phase is measured by the multi-tone phase difference measurement unit 50B. Since each tone signal is resampled in accordance with a signal obtained by dividing the frequency of the interference signal, it is possible to reduce fluctuations in the phase of each tone signal caused by instability in the sweep speed of the optical variable delay unit 4, etc., and improve the S / N ratio, thereby improving the accuracy of the phase characteristic calibration. [Industrial Applicability]

[0308] INDUSTRIAL APPLICABILITY As described above, the present invention has the advantage that a CW light source is not required for an interferometer and is highly cost-effective, and is useful for phase characteristic calibration devices and phase characteristic calibration methods in general. [Explanation of symbols]

[0309] 1, 1A, 1B, 1C, 1D, 1E, 1G Phase characteristic calibration device 2. Short pulse light source (pulsed light source) 3 Optical splitter 4, 204 Optical variable delay device (variable delay device) 5 Synchronization processing section 10 3-tone intermediate frequency signal generator 10B Multi-tone intermediate frequency signal generation and reference signal modulation section (multi-tone intermediate frequency signal generation section) 11a, 11b, 11c, 11d Intermediate frequency signal generator 12a, 12b Reference signal generator 13a, 13b, 13c, 13d Modulators 14a, 14b 90 degree phase shifter 15 Adder 16 Reference Sync Signal Generator 17 Reference signal modulation section 18 Local oscillator signal generator 19 Modulator 20 Calibration signal generation section 21 Frequency conversion section 22 Local oscillator signal generator 30 Electro-optical sampling section 31 Electro-optic crystals 32 Polarization separation section 33 Receiver 40 Lock-in detector 40B Multi-tone signal separation section (lock-in detection section) 41a, 41b Reference signal generator 42a, 42b phase shifter 43a, 43b 90 degree phase shifter 44a, 44b, 44c, 44d Modulators 45a, 45b, 45c, 45d Low-pass filters 50 3-tone phase difference measurement section 50B Multitone Phase Difference Measurement Unit 51a, 51b, 51c, 51d Phase detection unit 52 Phase difference calculation section 55 Phase correction value calculation section 60 Millimeter wave signal transmitter 70 Millimeter wave band signal measurement unit (signal measurement unit) 72 Frequency conversion section (down converter) 73 Intermediate frequency signal conversion section (down converter) 80 Millimeter wave band signal generator (signal generator) 82 Phase correction section 83 Local oscillator signal generator 84 Frequency conversion section (upconverter) 90 Millimeter wave signal receiver 91 Local oscillator signal generator 92 Frequency conversion section 93 Intermediate frequency signal conversion section 100 Delay amount correction section 101 CW light source 102, 103, 104 Optical demultiplexer 105 Optical multiplexer 105A, 105B Optical multiplexer / demultiplexer 106 Receiver 106A differential receiver 107 Frequency divider 108, 108A, 108B, 108a, 108b, 108c optical BPF 108d Wavelength Filter 110, 110A, 110B, 110C, 110D, 110E Interferometers 111, 111a, 111b, 111c, 111d A / D converter 112 Low-pass filter 113 A / D converter (second A / D converter) 114 Hilbert Transformer 115 Equal phase interval detection unit 116, 116a, 116b, 116c, 116d Resampling section 120, 120A, 120B, 120C Multitone signal sampling section 130, 130C Resampling processing section

Claims

1. A pulse light source (2) that generates pulsed light having a predetermined repetition frequency; an optical splitter (3) for splitting the pulsed light; a calibration signal generating section (20) including a multi-tone intermediate frequency signal generating section (10, 17) for multiplexing three or more intermediate frequency signals having different frequencies and outputting a multi-tone intermediate frequency signal modulated by a reference signal, and for up-converting the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency and a frequency converting section (21) to generate a calibration signal; a synchronization processing unit (5) which receives one of the pulsed lights output from the optical branching unit and controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulsed light; an electro-optic sampling unit (30) that receives the other of the pulsed lights output from the optical branching device, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay unit (4) to which one or the other of the pulsed lights output from the optical splitter is input and which changes a relative time difference between the pulsed light input to the electro-optic sampling unit and the calibration signal; a lock-in detection unit (40) that acquires the electrical signal while changing the relative time difference and modulates the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the three or more intermediate frequency signals included in the electrical signal; an interferometer (110) in which CW light is input to a first optical path including the variable delay device and a second optical path not including the variable delay device, and the CW light output from the first optical path and the CW light output from the second optical path are multiplexed and interfered with each other, and output as interference light; a light receiver (106) for detecting the intensity of the interference light; A frequency divider (107) that divides the frequency of the interference signal output from the optical receiver; a multi-tone signal sampling unit (120; 120A) that samples the multi-tone signal output from the lock-in detection unit in accordance with an output of the frequency divider and outputs the sampled multi-tone signal as a corrected multi-tone signal; a multi-tone phase difference measuring unit (50) for detecting a phase difference between three or more tone signals corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal; a phase correction value calculation unit (55) that calculates a phase correction value for correcting the frequency characteristic of the phase of a down converter (72, 73) of a signal measurement unit (70) from the phase difference between the tone signals; A phase characteristic calibration device (1; 1A) for calibrating a frequency characteristic of a phase of the down converter of the signal measurement unit that down-converts and measures a signal under test, the pulsed light input to the variable delay device is used in place of the CW light, and the interferometer includes an optical bandpass filter (108) that expands a pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

2. A pulse light source (2) that generates pulsed light having a predetermined repetition frequency; an optical splitter (3) for splitting the pulsed light; a multi-tone intermediate frequency signal generating section (10B) for outputting a multi-tone intermediate frequency signal obtained by modulating and combining three or more intermediate frequency signals having different frequencies with the same number of mutually orthogonal reference signals as the intermediate frequency signals, and a calibration signal generating section (20B) for up-converting the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency and a frequency converting section (21) to generate a calibration signal; a synchronization processing unit (5) which receives one of the pulsed lights output from the optical branching unit and controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulsed light; an electro-optic sampling unit (30) that receives the other of the pulsed lights output from the optical branching device, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay unit (4) to which one or the other of the pulsed lights output from the optical branching unit is input and which changes a relative time difference between the pulsed light input to the electro-optic sampling unit and the calibration signal; a multi-tone signal separation unit (40B) that acquires the electrical signal while changing the relative time difference, and modulates the electrical signal with sine waves having the same frequency as each of the reference signals and which are orthogonal to each other, thereby separating tone signals corresponding to the three or more intermediate frequency signals contained in the electrical signal; an interferometer (110) in which CW light is input to a first optical path including the variable delay device and a second optical path not including the variable delay device, and the CW light output from the first optical path and the CW light output from the second optical path are multiplexed and interfered with each other, and output as interference light; a light receiver (106) for detecting the intensity of the interference light; A frequency divider (107) that divides the frequency of the interference signal output from the optical receiver; a multi-tone signal sampling unit (120B; 120C) that samples each of the tone signals output from the multi-tone signal separation unit in accordance with an output of the frequency divider and outputs the sampled tone signals as corrected tone signals; a multi-tone phase difference measurement unit (50B) for detecting a phase difference between the corrected tone signals; a phase correction value calculation unit (55) that calculates a phase correction value for correcting the frequency characteristic of the phase of a down converter (72, 73) of a signal measurement unit (70) from a phase difference between the corrected tone signals; A phase characteristic calibration device (1B; 1C) for calibrating a frequency characteristic of a phase of the down converter of the signal measurement unit that down-converts and measures a signal under test, the pulsed light input to the variable delay device is used in place of the CW light, and the interferometer includes an optical bandpass filter (108) that expands a pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

3. A pulse light source (2) that generates pulsed light having a predetermined repetition frequency; an optical splitter (3) for splitting the pulsed light; a multi-tone intermediate frequency signal generating unit (10, 17) that multiplexes three or more intermediate frequency signals having different frequencies and outputs a multi-tone intermediate frequency signal modulated by a reference signal; a signal generating section (80) which up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, and an up-converter (84) of the signal generating section up-converts the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency to generate a calibration signal; a synchronization processing unit (5) which receives one of the pulsed lights output from the optical branching unit and controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulsed light; an electro-optic sampling unit (30) that receives the other of the pulsed lights output from the optical branching device, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay unit (4) to which one or the other of the pulsed lights output from the optical branching unit is input and which changes a relative time difference between the pulsed light input to the electro-optic sampling unit and the calibration signal; a lock-in detection unit (40) that acquires the electrical signal while changing the relative time difference and modulates the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the three or more intermediate frequency signals included in the electrical signal; an interferometer (110) in which CW light is input to a first optical path including the variable delay device and a second optical path not including the variable delay device, and the CW light output from the first optical path and the CW light output from the second optical path are multiplexed and interfered with each other, and output as interference light; a light receiver (106) for detecting the intensity of the interference light; A frequency divider (107) that divides the frequency of the interference signal output from the optical receiver; a multi-tone signal sampling unit (120; 120A) that samples the multi-tone signal output from the lock-in detection unit in accordance with an output of the frequency divider and outputs the sampled multi-tone signal as a corrected multi-tone signal; a multi-tone phase difference measuring unit (50) for detecting a phase difference between three or more tone signals corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal; a phase correction value calculation unit (55) that calculates a phase correction value for correcting a frequency characteristic of the phase of the up-converter of the signal generating unit from a phase difference between the tone signals; In a phase characteristic calibration device (1D; 1F) comprising: the pulsed light input to the variable delay device is used in place of the CW light, and the interferometer includes an optical bandpass filter (108) that expands a pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

4. A pulse light source (2) that generates pulsed light having a predetermined repetition frequency; an optical splitter (3) for splitting the pulsed light; a multi-tone intermediate frequency signal generating unit (10B) for outputting a multi-tone intermediate frequency signal obtained by modulating and multiplexing three or more intermediate frequency signals having different frequencies with the same number of mutually orthogonal reference signals as the intermediate frequency signals; a signal generating section (80) which up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, and an up-converter (84) of the signal generating section up-converts the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency to generate a calibration signal; a synchronization processing unit (5) which receives one of the pulsed lights output from the optical branching unit and controls the frequencies of the three or more intermediate frequency signals and the local signal so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of the repetition frequency of the pulsed light; an electro-optic sampling unit (30) that receives the other of the pulsed lights output from the optical branching device, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay unit (4) to which one or the other of the pulsed lights output from the optical branching unit is input and which changes a relative time difference between the pulsed light input to the electro-optic sampling unit and the calibration signal; a multi-tone signal separation unit (40B) that acquires the electrical signal while changing the relative time difference, and modulates the electrical signal with sine waves having the same frequency as each of the reference signals and which are orthogonal to each other, thereby separating tone signals corresponding to the three or more intermediate frequency signals contained in the electrical signal; an interferometer (110) in which CW light is input to a first optical path including the variable delay device and a second optical path not including the variable delay device, and the CW light output from the first optical path and the CW light output from the second optical path are multiplexed and interfered with each other, and output as interference light; a light receiver (106) for detecting the intensity of the interference light; A frequency divider (107) that divides the frequency of the interference signal output from the optical receiver; a multi-tone signal sampling unit (120B; 120C) that samples each of the tone signals output from the multi-tone signal separation unit in accordance with an output of the frequency divider and outputs the sampled tone signals as corrected tone signals; a multi-tone phase difference measurement unit (50B) for detecting a phase difference between the corrected tone signals; a phase correction value calculation unit (55) that calculates a phase correction value for correcting a frequency characteristic of the phase of the up-converter of the signal generating unit from a phase difference between the corrected tone signals; In a phase characteristic calibration device (1E; 1G) comprising: the pulsed light input to the variable delay device is used in place of the CW light, and the interferometer includes an optical bandpass filter (108) that expands a pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

5. 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter is provided in at least one of the first optical path and the second optical path, or between a multiplexing section that multiplexes the pulsed light output from the first optical path and the pulsed light output from the second optical path, and the optical receiver.

6. 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter limits a spectral width of the pulsed light and passes a plurality of line spectral components of the pulsed light.

7. 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter includes a first etalon (108a) having a free spectral range (FSR) narrower than a spectral width of the pulsed light, and a second etalon (108b) having a free spectral range (FSR) narrower than the spectral width of the pulsed light and having a free spectral range (FSR) different from that of the first etalon.

8. 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter includes an etalon (108c) having a free spectral range (FSR) narrower than a spectral width of the pulsed light, and a wavelength filter (108d) having a passband narrower than twice the free spectral range (FSR) of the etalon.

9. The interferometer comprises: a first optical demultiplexer (103) provided at a branching point between the first optical path and the second optical path, demultiplexing the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputting the first pulsed light toward the first optical path and outputting the second pulsed light toward the second optical path; a second optical demultiplexer (104) that is provided on the first optical path on the opposite side to the first optical demultiplexer side with the variable delay device between them, inputs the first pulse light that has passed through the variable delay device, demultiplexes the input first pulse light into a third pulse light and a fourth pulse light, and outputs the third pulse light to the first optical path; an optical multiplexer (105) provided at a joining portion of the first optical path and the second optical path, the optical multiplexer multiplexing the second pulse light separated by the first optical demultiplexer and the third pulse light separated by the second optical demultiplexer to generate a fifth pulse light; an optical bandpass filter provided between the optical multiplexer and the optical receiver, receiving the fifth pulsed light and generating the interference light; Equipped with 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter expands the pulse width of both the pulsed light output from the first optical path and the pulsed light output from the second optical path.

10. The interferometer comprises: a first optical demultiplexer (103) provided at a branching point between the first optical path and the second optical path, demultiplexing the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputting the first pulsed light toward the first optical path and outputting the second pulsed light toward the second optical path; an optical multiplexer / demultiplexer (105A) provided at a junction of the first optical path and the second optical path, receiving the first pulsed light that has passed through the variable delay device and the second pulsed light that has been demultiplexed by the first optical demultiplexer, and multiplexing the input first pulsed light and the second pulsed light to generate a third pulsed light and a fourth pulsed light; an optical bandpass filter that is provided between the optical multiplexer / demultiplexer and the optical receiver, to which the third pulsed light is input and that generates the interference light; Equipped with 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter expands the pulse width of both the pulsed light output from the first optical path and the pulsed light output from the second optical path.

11. The interferometer comprises: a first optical demultiplexer (103) provided at a branching point between the first optical path and the second optical path, demultiplexing the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputting the first pulsed light toward the first optical path and outputting the second pulsed light toward the second optical path; a second optical demultiplexer (104) that is provided on the first optical path on the opposite side to the first optical demultiplexer side with the variable delay device between them, inputs the first pulse light that has passed through the variable delay device, demultiplexes the input first pulse light into a third pulse light and a fourth pulse light, and outputs the third pulse light to the first optical path; the optical bandpass filter is provided on the first optical path on the opposite side of the variable delay device with the second optical demultiplexer therebetween, or on the second optical path; an optical multiplexer (105) provided at a junction of the first optical path and the second optical path, the optical multiplexer multiplexing a fifth pulsed light output from the optical bandpass filter provided on one of the first optical path and the second optical path and a sixth pulsed light output from the other of the first optical path and the second optical path to generate the interference light; Equipped with 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter expands a pulse width of either the pulsed light output from the first optical path or the pulsed light output from the second optical path.

12. The interferometer comprises: a first optical demultiplexer (103) provided at a branching point between the first optical path and the second optical path, demultiplexing the pulsed light output from the pulse light source into a first pulsed light and a second pulsed light, outputting the first pulsed light toward the first optical path and outputting the second pulsed light toward the second optical path; a second optical demultiplexer (104) that is provided on the first optical path on the opposite side to the first optical demultiplexer side with the variable delay device between them, inputs the first pulse light that has passed through the variable delay device, demultiplexes the input first pulse light into a third pulse light and a fourth pulse light, and outputs the third pulse light to the first optical path; a first optical bandpass filter (108A) that is provided on the first optical path on the opposite side of the variable delay device with the second optical demultiplexer therebetween, to which the third pulsed light is input and which outputs a fifth pulsed light; a second optical bandpass filter (108B) provided in the second optical path, receiving the second pulsed light and outputting a sixth pulsed light; an optical multiplexer (105) provided at a junction of the first optical path and the second optical path, the optical multiplexer multiplexing the fifth pulsed light output from the first optical bandpass filter and the sixth pulsed light output from the second optical bandpass filter to generate the interference light; Equipped with 5. The phase characteristic calibration device according to claim 1, wherein the optical bandpass filter includes the first optical bandpass filter (108A) and the second optical bandpass filter (108B), the first optical bandpass filter expands a pulse width of the pulsed light output from the first optical path, and the second optical bandpass filter expands a pulse width of the pulsed light output from the second optical path.

13. 12. The phase characteristic calibration device according to claim 11, wherein the optical multiplexer is an optical multiplexer / demultiplexer (105B) that multiplexes the fifth pulse light and the sixth pulse light to generate a first interference light and a second interference light as the interference light, and the optical receiver is a differential optical receiver (106A) that receives the first interference light and the second interference light and differentially detects intensities of the interference lights.

14. 13. The phase characteristic calibration device according to claim 12, wherein the optical multiplexer is an optical multiplexer / demultiplexer (105B) that multiplexes the fifth pulse light and the sixth pulse light to generate a first interference light and a second interference light as the interference light, and the optical receiver is a differential optical receiver (106A) that receives the first interference light and the second interference light and differentially detects intensities of the interference lights.

15. A pulsed light having a predetermined repetition frequency is split by an optical splitter (3), Three or more intermediate frequency signals having different frequencies are combined, and a multi-tone intermediate frequency signal modulated with a reference signal is output. The multi-tone intermediate frequency signal is up-converted using a local oscillator signal of a predetermined frequency and a frequency conversion section (21) to generate a calibration signal. controlling the frequencies of the three or more intermediate frequency signals and the local signal using one of the pulsed lights output from the optical branching device so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of a repetition frequency of the pulsed light; sampling the calibration signal by an electro-optic effect using the other of the pulsed lights output from the optical branching device, and outputting the sampled calibration signal as an electrical signal; acquiring the electrical signal while changing a relative time difference between the calibration signal and the pulsed light used for sampling the calibration signal by a variable delay device to which one or the other of the pulsed lights output from the optical branching device is input; modulating the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the three or more intermediate frequency signals contained in the electrical signal; inputting CW light into a first optical path including the variable delay device and a second optical path not including the variable delay device, causing the CW light output from the first optical path and the CW light output from the second optical path to interfere with each other and outputting them as interference light, detecting the intensity of the interference light as an interference signal, sampling the multi-tone signal according to a signal obtained by dividing the frequency of the interference signal to generate a corrected multi-tone signal, detecting a phase difference between three or more tone signals corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal; calculating a phase correction value for correcting the frequency characteristic of the phase of the down converter (72, 73) of the signal measurement unit (70) from the phase difference between the tone signals; A phase characteristic calibration method for calibrating a frequency characteristic of a phase of the down-converter of the signal measurement unit that down-converts and measures a signal under test, comprising: a phase characteristic calibration method, characterized in that the pulsed light input to the variable delay device is used in place of the CW light, and optical bandpass filtering is performed to expand a pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

16. A pulsed light having a predetermined repetition frequency is split by an optical splitter (3), three or more intermediate frequency signals having different frequencies are combined, a multi-tone intermediate frequency signal is generated by modulating the multi-tone intermediate frequency signal with a reference signal, and a calibration signal is generated by up-converting the multi-tone intermediate frequency signal with an up-converter (84) of a signal generating unit (80) using a local oscillator signal of a predetermined frequency; controlling the frequencies of the three or more intermediate frequency signals and the local signal using one of the pulsed lights output from the optical branching device so that the frequencies of the up-converted intermediate frequency signals included in the calibration signal become integer multiples of a repetition frequency of the pulsed light; sampling the calibration signal by an electro-optic effect using the other of the pulsed lights output from the optical branching device, and outputting the sampled calibration signal as an electrical signal; acquiring the electrical signal while changing a relative time difference between the calibration signal and the pulsed light used for sampling the calibration signal by a variable delay device to which one or the other of the pulsed lights output from the optical branching device is input; modulating the electrical signal with a sine wave having the same frequency as the reference signal to detect a multi-tone signal corresponding to the three or more intermediate frequency signals contained in the electrical signal; inputting CW light into a first optical path including the variable delay device and a second optical path not including the variable delay device, causing the CW light output from the first optical path and the CW light output from the second optical path to interfere with each other and outputting them as interference light, detecting the intensity of the interference light as an interference signal, sampling the multi-tone signal according to a signal obtained by dividing the frequency of the interference signal to generate a corrected multi-tone signal, detecting a phase difference between three or more tone signals corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal; calculating a phase correction value for correcting the frequency characteristic of the phase of the up-converter of the signal generating unit from the phase difference between the tone signals; A phase characteristic calibration method for calibrating a frequency characteristic of a phase of the up-converter of the signal generating unit, which up-converts a measurement intermediate frequency signal and outputs the up-converted signal as a measurement signal, comprising: a phase characteristic calibration method, characterized in that the pulsed light input to the variable delay device is used in place of the CW light, and optical bandpass filtering is performed to expand a pulse width of at least one of the pulsed light output from the first optical path and the pulsed light output from the second optical path so that the pulsed light output from the first optical path and the pulsed light output from the second optical path interfere with each other.

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