Phase characteristic calibration device and phase characteristic calibration method

Abstract

To provide a phase characteristic calibration device with which it is possible to improve the performance of separating into CW light and short-pulse light by using an optical component having high cost effectiveness, without increasing the complexity of an optical system.SOLUTION: The phase of a multitone signal for calibration is measured using an electrooptical sampling method. CW light is inputted to a first optical path in which a variable delay device 4 is included and a second optical path in which the variable delay device is not included, and CW light outputted from the first optical path and CW light outputted from the second optical path are interfered by an interferometer 110, with the result outputted as interference light. The intensity of the interference light is detected by an optical receiver 106 and outputted as an interference signal, the frequency of which is then divided by a frequency demultiplier 107. The multitone signal obtained by an electrooptical sampling unit 30, etc. is sampled in accordance with the output of the frequency demultiplier, and the multitone signal is corrected. In the interferometer, the propagation direction of the pulse light inputted to the variable delay device included in the first optical path and the propagation direction of the CW light inputted to the first optical path are mutually opposite.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

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

[0003] Generally, as frequencies become higher and wider, 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 transmission characteristics, so accurate calibration of the phase characteristics is required.

[0004] Typically, test equipment for testing the performance of millimeter-wave band receivers is equipped with a millimeter-wave band signal generator to generate measurement signals, and test equipment for testing the performance of millimeter-wave band transmitters is equipped with a millimeter-wave band signal measuring instrument to measure the signal under test. It is easy to connect these millimeter-wave band signal generator and millimeter-wave band signal measuring instrument and calibrate their frequency characteristics simultaneously. However, 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 minimal phase error and input it to the millimeter-wave band receiver. Furthermore, 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 instrument and accurately measure the millimeter-wave band modulated signal (signal under test) 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 characteristics 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 illustrating an electro-optic sampling method used to measure the time waveform of an electrical pulse used as a calibration signal. A pulsed beam emitted from a short-pulse light source (not shown) is branched. One of the branched pulsed beams is input to a DUT (Device Under Test) 201, such as a photodiode, while the other pulsed beam is input as a sampling pulsed beam via an optical variable delay 204 to an electric field detector 202, such as an electro-optic crystal. The DUT 201 outputs a millimeter-waveband electric pulse in response to the input pulsed beam, 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 in response to the sampling pulsed beam based on the electro-optic effect. The optical variable delay 204 then changes the delay amount (delay time) of the sampling pulsed beam, thereby shifting the sampling time of the millimeter-waveband electric pulse and detecting the electric field intensity of the electric pulse. In this manner, the time waveform of the millimeter-waveband electric pulse can be measured.

[0007] FIG. 2(a) is a timing chart of the signals in FIG. 1. The diagram in the first row from the top of FIG. 2(a) shows the 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 diagram in the second row of FIG. 2(a) shows the electrical pulse, which is the signal under test output from the DUT 201, which is an electrical pulse with a repetition frequency f. The diagram in the third row of FIG. 2(a) shows the 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 diagram in the fourth row of FIG. 2(a), the electric field detected by the electric field detector 202 is the electric field at a time in the electrical pulse corresponding to the delayed sampling pulse light (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 used 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. 20 shows a first configuration example of a conventional phase characteristic calibration device. The conventional phase characteristic calibration device 1000A calibrates the phase characteristics of a downconverter (frequency conversion unit 72, intermediate frequency signal conversion unit 73) of a millimeter wave band signal measurement unit 70 that measures a signal under measurement by frequency converting (downconverting) it. To this end, the phase characteristic calibration device 1000A 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 three-tone phase difference measurement unit 50, and a phase correction value calculation unit 55. Each of the components shown in Fig. 20 will now be described.

[0011] A short pulse light source 2 outputs short pulse light P1 at a predetermined repetition rate. 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 input to an optical variable delay device 4 and a synchronization processing unit 5, respectively. The optical variable delay device 4 continuously changes the delay time of the light by mechanically moving the position of a mirror 4a.

[0012] Calibration signal generating section 20 includes three-tone intermediate frequency signal generating section 10, reference signal modulating section 17, frequency converting section 21, and local oscillator signal generating section 22. Three-tone intermediate frequency signal generating section 10 includes intermediate frequency signal generators 11a to 11c and adder 15. Intermediate frequency signal generators 11a to 11c generate sine waves of different frequencies with a predetermined phase difference, and adder 15 adds the three sine waves to generate three-tone intermediate frequency signal S 10 Output as

[0013] The reference signal modulation unit 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 position in FIG. 20, 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 is the reference signal S 18 and 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 position in FIG. 20, the modulator 19 is bypassed and the three-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 oscillation signal S from a local oscillation 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 Output as

[0015] The synchronization processing unit 5 generates a three-tone intermediate frequency signal S 10 and local oscillator signal S 22 and the repetition frequency of the short pulse light source 2, a millimeter wave band 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 with the local oscillator signal S 22 The local oscillator 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 position in FIG. 20 and the switches SW1 and SW2 are set to the upper position 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 is applied to the electro-optic crystal 31, and the short pulse light P4 from the optical variable 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 photodetector 33 via the polarization separator 32. When the 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 photodetector 33. The electrical signal S output from the photodetector 33 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 unit 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 from the reference synchronization signal generator 16. 17 According to the reference synchronization 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 and 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 is the reference signal S 42 and a low-pass filter 45 extracts the low-frequency components.

[0019] The three-tone phase difference measuring unit 50 includes phase detection units 51a to 51c and a phase difference calculation unit 52. The phase detection unit 51a detects the electrical signal S 30 Similarly, phase detector 51b and phase detector 51c detect the phases of the second and third tones, respectively. Phase difference calculator 52 calculates the second derivative of each of the phases of the three tones and outputs the phase difference measurement result S using electro-optic sampling unit 30. 50 Specifically, the above processing is performed to output the calibration signal S 20 The frequency of these three tones is changed and repeated to measure the second derivative of the phase over a predetermined frequency range. The frequency characteristics of the phase can be obtained by integrating the second derivative of the phase twice. The phase difference measurement result S 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. 20, 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 converting unit 72, an intermediate frequency signal converting unit 73, and a phase correcting unit 74. The frequency converting unit 72 converts the CW local oscillator signal S 71 Using this, 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 or the like 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 from the electro-optic sampling unit 30 30 Similarly to the phase difference measurement in the previous section, the phase detectors 51a to 51c detect the phases of the three tones, and the phase difference calculator 52 calculates the second order differential of the phases of the three tones, and the calibration signal S 20 The frequency of the three tones is changed and repeated, and the second-order differential 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, set the switches SW11 and SW12 to the lower side of FIG. 20, and the switches SW1 and SW2 to the upper side of 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 Next, the switches SW11 and SW12 are set to the upper side in the same figure, 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. 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 characteristics of the calibration signal S 20and the frequency characteristics 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 measurement unit 70 are calculated from the frequency characteristics of the downconverter and the phase correction value calculation unit 55. The phase correction value calculation 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 measurement unit 70.

[0024] The signal S under test transmitted from the millimeter wave band signal transmitting unit 60 60 When measuring, the switches SW3 and SW4 are set to the lower position in FIG. 20. 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 signal under test 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 the output signal S 70' is input to the phase correction unit 74. The phase correction unit 74 divides the result by the frequency characteristic of the downconverter 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.

[0025] <Second configuration example> 21 shows a second configuration example of a conventional phase characteristic calibration apparatus. The conventional phase characteristic calibration apparatus 1000B calibrates the phase characteristics of a downconverter (frequency conversion unit 72, intermediate frequency signal conversion unit 73) of a millimeter wave band signal measurement unit 70 using a four-tone signal as a calibration signal. For this purpose, the phase characteristic calibration apparatus 1000B includes a short pulse light source 2, an optical branching unit 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 apparatus 1000B according to the second configuration example differs 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. The other configurations are the same as those of the first configuration example. Therefore, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0026] Calibration signal generation section 20B includes multi-tone intermediate frequency signal generation / reference signal modulation section 10B, multi-tone intermediate frequency signal generation section 25, frequency conversion section 21, and local oscillator signal generation section 22. Multi-tone intermediate frequency signal generation / reference signal modulation section 10B includes intermediate frequency signal generators 11a-11d, reference signal generators 12a and 12b, 90-degree phase shifters 14a and 14b, modulators 13a-13d, adder 15, and 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 (for example, sine waves) having different frequencies and a predetermined phase difference. 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 but 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 these signals in an adder 15 to generate a multi-tone intermediate frequency signal S 10 The reference signals S5 and S7 and the orthogonal reference signals S6 and 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 It is set to output the following.

[0029] When the switches SW10 and SW1 are set to the upper positions in FIG. 21, 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 generate 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 from the local oscillation signal generation unit 22. 22 The multi-tone intermediate frequency signal S from the multi-tone intermediate frequency signal generating unit 25 is generated using the 15 is up-converted to the millimeter wave band to generate the calibration signal S 21 The 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 from the reference synchronization signal generator 16. 17 According to the above, the reference signal S5 is a sine wave having the same frequency as the reference signal S5. 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 and adjust the phase of the reference signal S 42 Output as

[0031] The modulator 44a receives the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 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 modulates the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 42 and a reference signal S 43 and the low-frequency components are extracted by a 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, the reference signal S7 is a sine wave having the same frequency as the reference signal S7. 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 and adjust the phase of the reference signal S 44 Output as

[0033] The modulator 44c receives the electrical signal S from the electro-optic sampling unit 30.30 is the reference signal S 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 modulates the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 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 by the low-pass filter 45d. 42 ~S 45 are orthogonal to each other in all combinations. 30 The four-tone signals that have passed through low-pass filters 45a to 45d are sent to multi-tone phase difference measuring section 50B via 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 from the electro-optic sampling unit 30. 30 The phase difference calculation unit 52 calculates the second derivative of the phase of each 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 characteristics of the phase. 50 Output as

[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. 21, and the switches SW3 and SW4 are set to the upper side in FIG. 15is sent to the frequency converter 21 via the switch SW10 and up-converted to the second calibration signal S 21 The 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 are input to the phase detectors 51a to 51d of the multi-tone phase difference measuring unit 50 via the switches SW4 and SW21 to 24, and the phases of the four tones are detected. Then, the phase difference calculating unit 52 calculates the second derivative of the phase of each 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 value of the phase is integrated twice to obtain the frequency characteristic of the phase. The phase difference measurement result S 50' Output as

[0036] The calibration method is as follows. First, the switches SW10, SW1, and SW21 to SW24 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 Next, the switches SW10, SW1, and SW21 to SW24 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. 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 characteristics of the calibration signal S 20 and the frequency characteristics 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 measurement unit 70 are calculated from the frequency characteristics of the downconverter and the phase correction value calculation unit 55. The phase correction value calculation 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 measurement unit 70.

[0037] The signal S under test transmitted from the millimeter wave band signal transmitting unit 60 60 When measuring, the switches SW3 and SW4 are set to the lower position in Fig. 21. 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 signal under test 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 the output signal S 70' is input to the phase correction unit 74. The phase correction unit 74 divides the result by the frequency characteristic of the downconverter 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.

[0038] <Third configuration example> 22 shows a third configuration example of a conventional phase characteristic calibration apparatus. The conventional phase characteristic calibration apparatus 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. To this end, the phase characteristic calibration apparatus 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 device 1000C according to the third configuration example differs from the first configuration example (FIG. 20) in that it calibrates the phase characteristic of the upconverter of the millimeter wave band signal generating unit 80, and calibrates the phase characteristic of the downconverter of the millimeter wave band signal measuring unit 70. The other configurations are the same as those of the first configuration example, and the same components are denoted by the same reference numerals, 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 oscillator 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. 83 The phase-corrected intermediate frequency signal is up-converted to generate the millimeter-wave measurement signal S 80' Generate the measurement signal S 80' is sent to the millimeter wave band signal receiving unit 90 via the switch SW7.

[0040] The millimeter wave band signal receiving section 90 includes a local signal generating section 91, a frequency converting section 92, and an intermediate frequency signal converting section 93. The millimeter wave band measurement signal S 80' is converted by the frequency converter 92 into the local oscillator signal S from the local oscillator signal generator 91. 91 , and then undergoes processing such as frequency conversion in the intermediate frequency signal conversion unit 93 to generate the intermediate frequency signal S 90 is output as

[0041] The calibration method is as follows. First, set the switches SW6 and SW7 to the upper position in the figure. 10 is the reference signal S 18 and modulated three-tone intermediate frequency signal S 19 is input to the frequency converter 84 of the millimeter wave band signal generator 80, and the frequency converted millimeter wave band signal S 80 Phase difference measurement result S 50 to millimeter wave signal S 80 This becomes the frequency characteristic of the up-converter (frequency conversion unit 84) of the millimeter wave band signal generation unit 80. The phase correction value calculation unit 55 calculates the frequency characteristic of the up-converter over a predetermined frequency range and outputs it to the phase correction unit 82 of the millimeter wave band signal generation 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 positions in FIG. 81 The intermediate frequency signal whose phase has been 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 frequency converter 92 receives the local oscillator signal S from the local oscillator signal generator 91. 91 , and then performs frequency conversion etc. in the intermediate frequency signal converter 93 to generate the 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 of reception by the millimeter wave band signal receiving unit 90, which is the measurement target, can be obtained.

[0043] <Fourth configuration example> 23 shows a fourth example configuration of a conventional phase characteristic calibration device. A conventional phase characteristic calibration device 1000D calibrates the phase characteristic of an up-converter (frequency conversion unit 84) of a millimeter wave band signal generation unit 80 by using a four-tone signal as a calibration signal. To this end, 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 generation / reference signal modulation unit 10B, 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. A phase characteristic calibration apparatus 1000D according to the fourth configuration example differs from the second configuration example (FIG. 21) in that the calibration signal generating section 20B 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, in that the phase characteristic calibration apparatus 1000D according to the fourth configuration example is the same as the second configuration example. Furthermore, 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. 22). The same components are denoted by the same reference numerals, and detailed descriptions thereof will be omitted where appropriate.

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

[0045] The calibration method is as follows. First, set the switches SW6 and SW7 to the upper side in Fig. 23. 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 generation unit 80 are calculated from the above. The phase correction value calculation unit 55 calculates the frequency characteristics of the frequency conversion unit 84 over a predetermined frequency range and outputs them to the phase correction unit 82 of the millimeter wave band signal generation 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 positions in FIG. 23. 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 wave band signal receiving unit 90, whereby the frequency characteristics of the frequency conversion unit 84 are corrected to produce a measurement signal S 80' The result of reception by the millimeter wave band signal receiving unit 90, which is the measurement target, can be obtained. In all of the configuration examples shown in Figures 20 to 23, the optical variable delay device 4 is placed between the optical branching device 3 and the electro-optic sampling unit 30, but since it is only necessary to change the relative time difference between the short pulse light input to the electro-optic sampling unit and the calibration signal / millimeter-wave band 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] Japanese Patent Application Publication No. 2020-193848 Summary of the Invention [Problem to be solved by the invention]

[0048] In 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 regular time intervals. However, in actual sweeping of an optical variable delay, unpredictable random fluctuations in the sweep speed, such as mechanical rattle, can occur. If the sweep speed of the optical variable delay is not constant, the time intervals for electro-optic sampling will not be constant, causing fluctuations in the phase of the electro-optically sampled tone signal and a decrease in the signal-to-noise ratio, which leads to a problem of degraded accuracy in phase characteristic calibration.

[0049] To address this issue, the present inventors have proposed a method for correcting the delay based on an interference signal obtained from the interference light generated by the interferometer, using an optical path in which the output of a CW laser passes through a variable optical delay device and an optical path in which it does not. Specifically, an interferometer is constructed using an optical path in which the output of a CW laser passes through a variable optical delay device and an optical path in which it does not. Sweeping the variable optical delay device at a nearly constant speed and inputting the output of the interferometer to a photodetector produces an interference signal with a nearly constant period. The peak of this interference signal waveform is observed when the optical path length difference is an integer multiple of the wavelength of the CW light. The interference signal is divided by an appropriate frequency divider, and the signal obtained by electro-optically sampling a millimeter-wave tone signal (calibration signal) is used as a clock signal for the A / D converter, and then A / D conversion is performed. The CW light and short-pulse light can be separated using a polarizing beam splitter (PBS) or a wavelength filter.

[0050] More specifically, the configuration is as shown in FIG. The phase characteristic calibration device 1000E corrects the phase frequency characteristics of the downconverter (frequency conversion unit 72, intermediate frequency signal conversion unit 73) of the millimeter wave band signal measurement unit 70, which measures the signal under test by frequency converting (downconverting) it. To this end, 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 delay amount 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 detecting 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 prior art shown in FIG. 20, and therefore the same reference numerals are used and their explanations will be omitted. Next, the delay amount correcting unit 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. 24, includes a CW light source 101, an interferometer 110, a photodetector 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 configured 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 the CW light output from the first optical path and the CW light output from the second optical path interfere with each other and are output as interference light.

[0054] Specifically, interferometer 110 includes optical demultiplexer 102, optical multiplexer 103 such as a half mirror, optical demultiplexer 104 such as a half mirror, and optical multiplexer 105. Optical demultiplexer 102 is provided at the branch point between the first optical path and the second optical path, and is configured to demultiplex the CW light output from CW light source 101 into first CW light and second CW light. Optical multiplexer 103 is provided on the first optical path, and receives as input the first CW light and short pulse light sent from short pulse light source 2 via optical demultiplexer 3, and multiplexes the first CW light and the short pulse light to output the combined light to the first optical path. The optical demultiplexer 104 is provided on the first optical path on the opposite side of the optical multiplexer 103 with the optical variable delay device 4 in between, 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 junction of the first optical path and the second optical path, and multiplexes the first CW light and short pulse light output by the optical demultiplexer 104 with the second CW light demultiplexed by the optical demultiplexer 102 to generate interference light. 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 photodetector 106 includes, for example, a low-speed photodiode, and 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 between the first optical path and the second optical path (the delay time of the optical variable delay device 4) 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 photodetector 106. If the division ratio of the frequency divider 107 is N (N is an integer), then a rectangular wave is output from the frequency divider 107, where the optical path length difference between the first optical path and the second optical path (the delay time of the optical variable delay device 4) rises every N times the wavelength (period) of the CW light.

[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 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 regular 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, it is possible to correct phase fluctuations in the multi-tone signal obtained by electro-optic sampling that are caused by instability in the sweep speed of the variable optical delay device 4.

[0059] FIG. 25 shows another configuration of the prior art. The calibration signal generator 20B, multi-tone signal separator 40B, and multi-tone phase difference measurer 50B are the same as those in Fig. 21, and their descriptions will be omitted. The short pulse light source 2, optical brancher 3, optical variable delay device 4, synchronization processor 5, electro-optic sampling unit 30, phase correction value calculator 55, and delay amount corrector 100 are the same as those in Fig. 24, and their descriptions will be omitted. The multi-tone signal sampler 120B samples each tone signal output from the multi-tone signal separator 40B in accordance with the output of frequency divider 107, and outputs four corrected tone signals.

[0060] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at regular 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, it is possible to correct phase fluctuations in the multi-tone signal obtained by electro-optic sampling that are caused by instability in the sweep speed of the variable optical delay device 4. 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] FIG. 26 shows another configuration of the prior art for calibrating the phase characteristics of the millimeter wave band signal generating section 80. The three-tone intermediate frequency signal generating unit 10, reference signal modulating unit 17, lock-in detecting unit 40, multi-tone signal sampling unit 120, short pulse light source 2, optical branching unit 3, optical variable delay unit 4, synchronization processing unit 5, electro-optic sampling unit 30, three-tone phase difference measuring unit 50, phase correction value calculating unit 55, and delay amount correcting unit 100 are the same as those in Fig. 24, and their explanations will be omitted. The millimeter wave band signal generating unit 80 and millimeter wave signal receiving unit 90 are the same as those in Fig. 22, and the phase characteristic calibration method for the millimeter wave band signal generating unit 80 is also the same.

[0062] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at regular 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, it is possible to correct phase fluctuations in the multi-tone signal obtained by electro-optic sampling that are caused by instability in the sweep speed of the variable optical delay device 4.

[0063] FIG. 27 shows another configuration of the prior art for calibrating the phase characteristics of the millimeter wave band signal generating section 80. The multi-tone intermediate frequency signal generating and reference signal modulating unit 10B, multi-tone signal separating unit 40B, multi-tone signal sampling unit 120B, multi-tone phase difference measuring unit 50B, 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 in Fig. 25 and will not be described again. The millimeter wave band signal generating unit 80 and millimeter wave signal receiving unit 90 are the same as those in Fig. 23, and the phase characteristic calibrating method for millimeter wave band signal generating unit 80 is also the same.

[0064] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at regular 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, it is possible to correct phase fluctuations in the multi-tone signal obtained by electro-optic sampling that are caused by instability in the sweep speed of the variable optical delay device 4. 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] 24 to 27, if a half mirror is used in the optical demultiplexer 104, the CW light is input to the electro-optic sampling unit 30, and the short-pulse light is input to the photoreceiver 106 of the delay amount correction unit 100. Even if the CW light is input to the electro-optic sampling unit 30 or the short-pulse light is input to the photoreceiver 106 of the delay amount correction unit 100, a multi-tone signal can be obtained by electro-optic sampling in the same way. However, in practice, there is a problem that the influence of noise and the like occurs. To solve this problem, a polarizing beam splitter can be used in the optical demultiplexer 104 to separate the CW light and the short-pulse light to some extent by polarization. However, actual polarizing beam splitters have a finite polarization extinction ratio, so there is a problem that the CW light and the short-pulse light cannot be completely separated.

[0066] In addition, there were issues that needed to be improved from the perspectives of loss of short pulse light, the complexity of the optical system, and cost-effectiveness due to the selection of optical components.

[0067] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a phase characteristic calibration device and a phase characteristic calibration method that can improve the performance of separating pulsed light and CW light using cost-effective optical components without making the optical system excessively complex. [Means for solving the problem]

[0068] 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 of different frequencies and outputs a multi-tone intermediate frequency signal modulated with a reference signal, a calibration signal generating unit (20) that up-converts the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency and a frequency converting unit (21) to generate a calibration signal, a synchronization processing unit (5) that receives one of the pulse light beams output from the optical branching unit and controls the frequencies of the three or more intermediate frequency signals and the local oscillator 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) that receives the other of the pulse light beams output from the optical branching unit and samples the calibration signal in accordance with the pulse light and outputs it as an electrical signal, and one or the other of the pulse light beams output from the optical branching unit. a variable delay (4) that receives the pulsed light and changes the relative time difference between the pulsed light and the calibration signal input to the electro-optic sampling unit; 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 intermediate frequency signals of three or more waves contained in the electrical signal; a CW light source (101) that generates CW light of a predetermined wavelength; the CW light is input to a second optical path not including the first optical path, the CW light output from the first optical path interferes with the CW light output from the second optical path, and the CW light is output as interference light; an interferometer (110) that detects the intensity of the interference light; a photoreceiver (106) 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 according to the output of the frequency divider and outputs the sampled 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 down-converters (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, and is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other;

[0069] With this configuration, in the phase characteristic calibration device according to the present invention, the interferometer has the pulsed light and the CW light propagating in the first optical path in opposite directions, making it possible to separate the CW light and the short pulsed light using cost-effective optical components without complicating the optical system.

[0070] Furthermore, 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 Figure 24. Because the phase fluctuations of 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 pulsed light of a predetermined repetition frequency, an optical branching unit (3) that branches the pulsed light, 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 of different frequencies with the same number of mutually orthogonal reference signals as the intermediate frequency signals, and a calibration signal generating unit (20B) that up-converts the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency and a frequency converting unit (21) to generate a calibration signal. a synchronization processing unit (5) that 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 oscillator 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 unit and samples the calibration signal according to the pulsed light and outputs it as an electrical signal; a variable delay unit (4) that receives one or the other of the pulsed lights output from the optical branching unit and changes the relative time difference between the pulsed light and the calibration signal input to the electro-optic sampling unit; a multi-tone signal separation unit (40B) that acquires the electrical signal while changing the relative time difference and separates tone signals corresponding to the three or more intermediate frequency signals included in the electrical signal by modulating the electrical signal with sine waves that are orthogonal to each other and have the same frequency as each of the reference signals; a CW light source (101) that generates CW light of a predetermined wavelength; the CW light is input to a second optical path not including a photodiode, and the CW light output from the first optical path interferes with the CW light output from the second optical path, and the CW light is output as interference light; an interferometer (110) that detects the intensity of the interference light; a photodetector (106) that divides the frequency of the interference signal output from the photodetector; and a multi-tone signal sampling unit (120B) that samples each of the tone signals output from the multi-tone signal separation unit according to the output of the frequency divider, and outputs the sampled signal as a corrected tone signal;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 characteristics of down-converters (72, 73) of a signal measurement unit (70) from the phase difference between the tone signals, wherein the phase characteristic calibration device (1B; 1C) calibrates the phase-frequency characteristics of the down-converter of the signal measurement unit that down-converts and measures a signal under measurement, and is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other;

[0072] With this configuration, in the phase characteristic calibration device according to the present invention, the interferometer has the pulsed light and the CW light propagating in the first optical path in opposite directions, making it possible to separate the CW light and the short pulsed light using cost-effective optical components without complicating the optical system.

[0073] 25, each tone signal output from the multi-tone signal separation unit is sampled according to the output of the frequency divider that divides the interference signal, so that each tone signal obtained by electro-optic sampling is sampled at a constant interval relative 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] 21, 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 unit, allowing the frequency interval to be narrowed without increasing the size of the variable delay unit.In other words, phase measurement is possible with high frequency resolution regardless of the sweep width of the variable delay unit.

[0075] To achieve the above object, the phase characteristic calibration device according to the present invention comprises 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 (10, 17) that combines three or more intermediate frequency signals of different frequencies and outputs a multi-tone intermediate frequency signal modulated with a reference signal, and a signal generating unit (80) that up-converts the measurement intermediate frequency signal and outputs it as a measurement signal, and the signal generating unit (80) uses a local oscillator signal of a predetermined frequency to convert the multi-tone intermediate frequency signal into an up-converter ( a synchronization processing unit (5) that 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 oscillator 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 lights; an electro-optic sampling unit (30) that receives the other of the pulsed lights output from the optical branching unit and samples the calibration signal according to the pulsed lights and outputs it as an electric signal; a variable delay (4) that receives one or the other of the pulsed lights output from the first and second optical fibers and 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) 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 intermediate frequency signals of three or more waves contained in the electrical signal; a CW light source (101) that generates CW light of a predetermined wavelength; an interferometer (110) that inputs the CW light to a second optical path not including a variable delay unit, causes the CW light output from the first optical path to interfere with the CW light output from the second optical path, and outputs the interfered light; a photoreceiver (106) that detects the intensity of the interfered light; a frequency divider (107) that divides the frequency of the interfered 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 sampled multi-tone signal as a corrected multi-tone signal.A phase characteristic calibration device (1D) comprising: 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 generation unit from the phase difference between the tone signals, wherein the interferometer is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other.

[0076] With this configuration, in the phase characteristic calibration device according to the present invention, the interferometer has the pulsed light and the CW light propagating in the first optical path in opposite directions, making it possible to separate the CW light and the short pulsed light using cost-effective optical components without complicating the optical system.

[0077] Furthermore, similar to FIG. 26, when correcting the phase frequency characteristics of the up-converter of the signal generating section that up-converts the measurement intermediate frequency signal and outputs it as a measurement signal, it is possible to reduce phase fluctuations 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] To achieve the above object, the phase characteristic calibration device according to the present invention comprises 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 of 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 the 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) that receives an input of 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 oscillator 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; an electro-optic sampling unit (30) that receives an input of the other of the pulsed lights output from the optical branching unit and samples the calibration signal according to the pulsed light and outputs it as an electrical signal; a variable delay unit (4) that receives an input of one or the other of the pulsed lights output from the optical branching unit and changes the relative time difference between the pulsed light and the calibration signal input to the electro-optic sampling unit; a multi-tone signal separation unit (40B) that acquires the electrical signal while changing the relative time difference and separates tone signals corresponding to the three or more intermediate frequency signals included in the electrical signal by modulating the electrical signal with sine waves that are orthogonal to each other and have the same frequency as each of the reference signals; an interferometer (110) that inputs the CW light to a first optical path including the variable delay device and a second optical path not including the variable delay device, causes the CW light output from the first optical path to interfere with the CW light output from the second optical path, and outputs 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 samples each of the tone signals output from the multi-tone signal separation unit according to the output of the frequency divider,a multi-tone signal sampling unit (120B) that outputs a corrected tone signal; a multi-tone phase difference measuring 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 that corrects the phase frequency characteristic of the up-converter of the signal generating unit from the phase difference between the tone signals, wherein the interferometer is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other.

[0079] With this configuration, in the phase characteristic calibration device according to the present invention, the interferometer has the pulsed light and the CW light propagating in the first optical path in opposite directions, making it possible to separate the CW light and the short pulsed light using cost-effective optical components without complicating the optical system.

[0080] Furthermore, as in FIG. 27, when correcting the phase frequency characteristics of the up-converter of the signal generating section that 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 fluctuations in the phase of each tone signal caused by instability in the sweep speed of the variable delay device, etc., and improving the S / N ratio.

[0081] 23, 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 unit, allowing the frequency interval to be narrowed without increasing the size of the variable delay unit.In other words, phase measurement is possible with high frequency resolution regardless of the sweep width of the variable delay unit.

[0082] In the phase characteristic calibration device according to the present invention, the interferometer includes an optical demultiplexer (102) provided at a branching point between the first optical path and the second optical path, which demultiplexes the CW light of a first polarization output from the CW light source into a first CW light and a second CW light; a first polarizing beam splitter (104B) provided on the first optical path, which receives, from different paths, the first CW light of the first polarization and the pulsed light of a second polarization orthogonal to the first polarization and sent in the reverse direction along the first optical path from the pulsed light source via the variable delay device, and outputs the first CW light of the first polarization in the forward direction along the first optical path and outputs the pulsed light of the second polarization toward the electro-optic sampling unit; and a second polarizing beam splitter (104B) provided on the first optical path on the opposite side of the first polarizing beam splitter side with the variable delay device interposed therebetween, which receives the first CW light of the first polarization that has passed through the variable delay device and both the first polarization and the second polarization output from the pulsed light source. a second polarizing beam splitter (103B) that inputs the pulsed light having one polarization component and the other polarization component from different paths, separates the input pulsed light into the pulsed light of the first polarization and the pulsed light of the second polarization, and outputs the first CW light of the first polarization in the forward direction of the first optical path and outputs the pulsed light of the second polarization in the reverse direction of the first optical path toward the variable delay device; and an optical multiplexer (105) that is provided at a junction of the first optical path and the second optical path and multiplexes the first CW light of the first polarization output by the second polarizing beam splitter and the second CW light of the first polarization separated by the optical demultiplexer to generate the interference light, wherein the pulsed light of the first polarization separated by the second polarizing beam splitter is input to the synchronization processing unit, so that the second polarizing beam splitter also functions as the optical branching device.

[0083] As described above, in the phase characteristic calibration device according to the present invention, the first CW light of the first polarization and the pulsed light of the second polarization are configured to propagate in opposite directions in the first optical path including the variable delay device, thereby achieving a large extinction ratio in the separation. Furthermore, the optical splitter is a second polarizing beam splitter, and the pulsed light of the first polarization split by the second polarizing beam splitter from the pulsed light having a predetermined polarization component is input to the synchronization processing unit. With this configuration, the phase characteristic calibration device according to the present invention does not require the optical splitter 3 shown in FIG. 6 , thereby simplifying the configuration compared to the basic configuration shown in FIG. 6 . Furthermore, the splitting ratio can be changed as needed by changing the ratio of the s-polarized component and the p-polarized component of the short pulsed light input to the second polarizing beam splitter, thereby enabling efficient use of the optical power of the pulsed light.

[0084] In the phase characteristic calibration device according to the present invention, the interferometer is provided at a branching point between the first optical path and the second optical path, and receives the CW light output from the CW light source and having polarization components of both the first polarization and a second polarization orthogonal to the first polarization, and the pulsed light of the second polarization sent from the pulsed light source in the reverse direction of the first optical path via the variable delay device, from different paths, and separates the input CW light into a first CW light of the first polarization and a second CW light of the second polarization, outputs the first CW light of the first polarization in the forward direction of the first optical path, outputs the second CW light of the second polarization to the second optical path, and converts the pulsed light of the second polarization into the electro-optical a half-wave plate (108) that is provided in the second optical path and converts the second CW light of the second polarization output from the polarizing beam splitter combiner to the second optical path into the first polarization; and an optical directional coupler (103C) that is provided at a junction of the first optical path and the second optical path and combines the first CW light of the first polarization with the second CW light of the first polarization to generate the interference light, and inputs the pulsed light of the second polarization sent from the pulse light source via the optical branching device, and outputs the pulsed light in the reverse direction of the first optical path.

[0085] As described above, in the phase characteristic calibration device according to the present invention, the first CW light of the first polarization and the pulsed light of the second polarization are configured to propagate in opposite directions in the first optical path including the variable delay device, thereby achieving a large extinction ratio in the separation. Furthermore, a half-wave plate is provided in the second optical path to convert the second CW light of the second polarization output from the polarization beam splitter / combiner to the second optical path into the first polarization. With this configuration, the phase characteristic calibration device according to the present invention does not require the optical demultiplexer 102 and optical multiplexer 105 in FIG. 6 , thereby simplifying the configuration compared to the basic configuration shown in FIG. 6 . Thus, the phase characteristic calibration device according to the present invention uses fewer optical elements and has a large extinction ratio in the separation compared to the basic configuration shown in FIG. 6 , thereby suppressing the effects of noise.

[0086] In the phase characteristic calibration device according to the present invention, the interferometer is provided at a branching point between the first optical path and the second optical path, and receives the CW light output from the CW light source and having polarization components of both the first polarization and a second polarization orthogonal to the first polarization, and the pulsed light of the second polarization sent from the pulse light source in the opposite direction of the first optical path via the variable delay device, through different paths, and separates the input CW light into a first CW light of the first polarization and a second CW light of the second polarization, and a first polarizing beam splitter (104D) that outputs the first CW light in the forward direction of the first optical path, outputs the second CW light of the second polarization to the second optical path, and outputs the pulsed light of the second polarization toward the electro-optic sampling unit; a half-wave plate (108) that is provided in the second optical path and converts the second CW light of the second polarization output from the first polarizing beam splitter to the second optical path into the first polarization; a second polarizing beam splitter that is provided on the opposite side to the input side, receives the first CW light of the first polarization that has passed through the variable delay device and the pulsed light that is output from the pulse light source and has polarization components of both the first polarization and the second polarization, and separates the input pulsed light into the pulsed light of the first polarization and the pulsed light of the second polarization, and outputs the first CW light of the first polarization in the forward direction of the first optical path and the pulsed light of the second polarization in the reverse direction of the first optical path; and an optical combiner (105) provided at a junction of the first optical path and the second optical path, which combines the first CW light of the first polarization sent from the second polarizing beam splitter and the second CW light of the first polarization sent from the half-wave plate to generate the interference light, wherein the pulsed light of the first polarization split by the second polarizing beam splitter is input to the synchronization processing unit, so that the second polarizing beam splitter also functions as the optical branching device.

[0087] As described above, in the phase characteristic calibration device according to the present invention, the first CW light of the first polarization and the pulsed light of the second polarization are configured to propagate in opposite directions in the first optical path including the variable delay device, thereby achieving a large extinction ratio in the separation. Furthermore, a half-wave plate is provided in the second optical path to convert the second CW light of the second polarization output from the first polarizing beam splitter to the second optical path into the first polarization. This configuration simplifies the configuration of the phase characteristic calibration device according to the present invention compared to the basic configuration shown in FIG. 6 by eliminating the optical splitter 102 shown in FIG. 6 . Furthermore, the optical splitter is a second polarizing beam splitter, and the first polarized pulsed light split from the pulsed light having a predetermined polarization component by the second polarizing beam splitter is input to the synchronization processing unit. This configuration simplifies the configuration of the phase characteristic calibration device according to the present invention compared to the basic configuration shown in FIG. 6 by eliminating the optical splitter 3 shown in FIG. 6 . Moreover, the splitting ratio can be changed as needed by changing the ratio of the s-polarized and p-polarized components of the pulsed light input to the second polarizing beam splitter, thereby enabling efficient use of the optical power of the pulsed light.

[0088] As described above, compared with the basic configuration shown in FIG. 6, the phase characteristic calibration device according to the present invention uses fewer optical elements, has less pulse loss, can input more power to the electro-optic crystal, can change the demultiplexing ratio by changing the polarization of the short pulse light, can use the optical power of the pulse light efficiently, and has a large extinction ratio because the pulse light and CW light propagate in different directions.

[0089] In the phase characteristic calibration device according to the present invention, the optical multiplexer may be an optical multiplexer / demultiplexer (105E) that multiplexes the first CW light separated by the second polarizing beam splitter and the second CW light separated by the optical demultiplexer to generate first interference light and second interference light as the interference light, and the photodetector may be a differential photodetector (109) that receives the first interference light and the second interference light as input and differentially detects the intensities of the interference lights.

[0090] With this configuration, the phase characteristic calibration device according to the present invention can remove common-mode noise, increase the strength of the interference signal, and improve the S / N ratio.

[0091] In the phase characteristic calibration device according to the present invention, the optical directional coupler combines the first CW light of the first polarization separated by the polarizing beam splitter combiner and the second CW light of the first polarization separated by the polarizing beam splitter combiner and passed through the half-wave plate to generate the first interference light of the first polarization and the second interference light of the first polarization as the interference light, and a polarizing beam splitter (3F) is used instead of the optical branching device, and the polarizing beam splitter combines the first interference light of the first polarization and the first and second polarizations output from the pulse light source. and the pulsed light having both polarization components, are input from different paths, the input pulsed light is separated into the pulsed light of the first polarization and the pulsed light of the second polarization, the pulsed light of the first polarization is output toward the synchronization processing unit, the pulsed light of the second polarization is output toward the optical directional coupler, and the first interference light of the first polarization is output, and the optical receiver may be a differential optical receiver (109) that receives the first interference light output from the polarizing beam splitter and the second interference light generated by the optical directional coupler and differentially detects the intensities of the interference lights.

[0092] With this configuration, the phase characteristic calibration device according to the present invention can eliminate common-mode noise, increase the intensity of the interference signal, and improve the S / N ratio. In particular, the problem of CW light entering a pulsed light source is resolved.

[0093] In the phase characteristic calibration device according to the present invention, the optical multiplexer may be an optical multiplexer / demultiplexer (105G) that multiplexes the first CW light output by the second polarizing beam splitter and the second CW light that has passed through the half-wave plate to generate first interference light and second interference light as the interference light, and the photodetector may be a differential photodetector (109) that receives the first interference light and the second interference light and differentially detects the intensities of the interference lights.

[0094] With this configuration, the phase characteristic calibration device according to the present invention can remove common-mode noise, increase the strength of the interference signal, and improve the S / N ratio.

[0095] A phase characteristic calibration method according to the present invention includes splitting pulsed light having a predetermined repetition frequency using an optical splitter (3), multiplexing three or more intermediate frequency signals having different frequencies, outputting a multi-tone intermediate frequency signal modulated with a reference signal, up-converting the multi-tone intermediate frequency signal using a local oscillator signal of 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 oscillator signal using one of the pulsed light 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 pulsed light, sampling the calibration signal by an electro-optic effect using the other of the pulsed light output from the optical splitter and outputting it as an electrical signal, obtaining the electrical signal while changing the relative time difference between the pulsed light used for sampling and the calibration signal using a variable delay device to which one or the other of the pulsed light output from the optical splitter is input, and modulating the electrical signal with a sine wave having the same frequency as the reference signal to modulate the three or more intermediate frequency signals included in the electrical signal. 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 the interfered light, detecting the intensity of the interfered light as an interference signal, sampling the multi-tone signal according to a signal obtained by dividing the frequency of the interfered signal to generate a corrected multi-tone signal, and generating a corrected multi-tone signal corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal. and calculating a phase correction value for correcting the phase-frequency characteristics of the downconverters (72, 73) of the signal measuring unit (70) that downconverts and measures a signal under measurement, from the phase differences between the tone signals of three or more waves, wherein the phase correction value is used to correct the phase-frequency characteristics of the downconverters (72, 73) of the signal measuring unit (70), and the method is characterized in that, in the output step of the interference light, the pulsed light input to the variable delay device included in the first optical path and the CW light input to the first optical path are propagated in directions opposite to each other.

[0096] With this configuration, when the phase characteristic calibration method according to the present invention corrects the phase frequency characteristics of the downconverter of the signal measurement unit that downconverts and measures the signal under measurement, the propagation directions of the pulsed light and the CW light in the first optical path are opposite to each other, making it possible to separate the CW light and the short pulse light using cost-effective optical components without complicating the optical system.

[0097] A phase characteristic calibration method according to the present invention includes splitting pulsed light having a predetermined repetition frequency with an optical splitter (3), multiplexing three or more intermediate frequency signals having different frequencies, generating a multi-tone intermediate frequency signal modulated with a reference signal, up-converting the multi-tone intermediate frequency signal with an up-converter (84) of a signal generating unit (80) using a local oscillator signal having a predetermined frequency to generate a calibration signal, and using one of the pulsed light output from the optical splitter to convert the frequency of each of the up-converted intermediate frequency signals included in the calibration signal to an integer multiple of the repetition frequency of the pulsed light. As described above, the frequencies of the three or more intermediate frequency signals and the local oscillator signal are controlled, the other of the pulsed lights output from the optical branching device is used to sample the calibration signal by an electro-optic effect, and the signal is output as an electrical signal. The electrical signal is obtained while changing the relative time difference between the pulsed light used for sampling and 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. The electrical signal is modulated with a sine wave having the same frequency as the reference signal, thereby modulating the three or more intermediate frequency signals included in the electrical signal. a multi-tone signal corresponding to the three or more intermediate frequency signals included in the corrected multi-tone signal; a CW light of a predetermined wavelength is input to a first optical path including the variable delay device and a second optical path not including the variable delay device; the CW light output from the first optical path and the CW light output from the second optical path are made to interfere with each other, and are output as interference light; the intensity of the interference light is detected as an interference signal; the multi-tone signal is sampled according to a signal obtained by dividing the frequency of the interference signal, and generated as a corrected multi-tone signal; a phase correction value for correcting the phase-frequency characteristics of the up-converter of the signal generating unit, which up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, the phase correction value including: detecting a phase difference between tone signals of at least one wavelength; and calculating a phase correction value for correcting the phase-frequency characteristics of the up-converter of the signal generating unit from the phase difference between the tone signals; and wherein, in the output step of the interference light, the pulsed light input to the variable delay device included in the first optical path and the CW light input to the first optical path are propagated in directions opposite to each other.

[0098] With this configuration, when the phase characteristic calibration method according to the present invention corrects the phase frequency characteristic of the up-converter of the signal generating unit that up-converts a measurement intermediate frequency signal and outputs it as a measurement signal, the propagation directions of the pulsed light and the CW light in the first optical path are opposite to each other, making it possible to separate the CW light and the short pulse light using cost-effective optical components without complicating the optical system. [Effects of the Invention]

[0099] According to the present invention, it is possible to provide a phase characteristic calibration device and a phase characteristic calibration method that can improve the performance of separating CW light and short pulse light using cost-effective optical components without complicating the optical system. [Brief explanation of the drawings]

[0100] [Figure 1] FIG. 1 is a diagram illustrating an electro-optic sampling method. [Figure 2] 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 the electric field while changing the delay time. [Figure 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. 1B. [Figure 4] 1 is a diagram showing an example of the overall configuration of a phase characteristic calibration device according to the present invention; [Figure 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 another configuration diagram of the interferometer of FIG. 5. [Figure 7] FIG. 10 is a configuration diagram of a phase characteristic calibration device according to a second embodiment of the present invention. [Figure 8] FIG. 10 is a configuration diagram of a phase characteristic calibration device according to a third embodiment of the present invention. [Figure 9] FIG. 10 is a configuration diagram of a phase characteristic calibration device according to a fourth embodiment of the present invention. [Figure 10]FIG. 10 is a configuration diagram of a phase characteristic calibration device according to a fifth embodiment of the present invention. [Figure 11] FIG. 10 is a configuration diagram of a phase characteristic calibration device according to a sixth embodiment of the present invention. [Figure 12] FIG. 11 is a configuration diagram of a phase characteristic calibration device according to a seventh embodiment of the present invention. [Figure 13] FIG. 13 is a configuration diagram of a phase characteristic calibration device according to an eighth embodiment of the present invention. [Figure 14] FIG. 10 is another configuration diagram of the interferometer (Modification 2). [Figure 15] FIG. 10 is another configuration diagram of the interferometer (Modification 3). [Figure 16] FIG. 10 is another configuration diagram of the interferometer (Modification 4). [Figure 17] FIG. 10 is another configuration diagram of the interferometer (Modification 5). [Figure 18] FIG. 10 is another configuration diagram of the interferometer (Modification 6). [Figure 19] FIG. 10 is another configuration diagram of the interferometer (Modification 7). [Figure 20] 1 shows a first configuration example of a conventional phase characteristic calibration device. [Figure 21] 1 shows a second configuration example of a conventional phase characteristic calibration device. [Figure 22] 10 shows a third configuration example of a conventional phase characteristic calibration device. [Figure 23] 10 shows a fourth configuration example of a conventional phase characteristic calibration device. [Figure 24] 10 shows a fifth example of the configuration of a conventional phase characteristic calibration device. [Figure 25] 10 shows a sixth example of the configuration of a conventional phase characteristic calibration device. [Figure 26] 10 shows a seventh configuration example of a conventional phase characteristic calibration device. [Figure 27] 10 shows an eighth example of the configuration of a conventional phase characteristic calibration device. DETAILED DESCRIPTION OF THE INVENTION

[0101] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0102] (Basic configuration) 3(a) is a diagram showing an example of the configuration of a conventional device, and (b) and (c) are diagrams showing examples of the configuration 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 a conventional device in which an optical variable delay device 4 is placed between an optical branching device 3 and a synchronization processing unit 5, the 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.

[0103] When the phase characteristic calibration device according to the embodiment of the present invention has an optical variable delay device 4 disposed between the optical branching device 3 and the synchronization processing unit 5, as shown in FIG. 3(b), in addition to the configuration of the conventional device shown in FIG. 3(a), it further includes a CW light source 101, an interferometer 110, an optical receiver 106, a frequency divider 107, and an A / D converter 111. The interferometer 110 includes a demultiplexer 102, a demultiplexer 103, a demultiplexer 104, and a multiplexer 105, and generates interference light by multiplexing CW 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. The CW light and the short pulse light input to the optical variable delay device 4 are configured to propagate in opposite directions. The intensity of the interference light is detected by the optical receiver 106, output as an interference signal, which is then frequency-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. Figure 3(c) shows the waveform of the interference signal, with the horizontal axis representing the optical path difference ΔL and the vertical axis representing the signal intensity. The interference signal is a sinusoidal repetitive signal whose intensity is maximized when the optical path difference ΔL is an integer multiple of the wavelength λ of the CW light.

[0104] 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 which 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, similarly to conventional devices, 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). The phase characteristic calibration device of this embodiment includes a CW light source 101, an interferometer 110 (including an optical demultiplexer 102, an optical demultiplexer 103, an optical demultiplexer 104, and an optical multiplexer 105), a photodetector 106 such as a low-speed PD, a frequency divider 107, and an A / D converter 111, and is configured so that the propagation directions of the CW light and the short pulse light input to the optical variable delay device 4 are opposite to each other.

[0105] The short-pulse light source 2 is, for example, a fiber laser that outputs short-pulse light at a predetermined repetition rate. The short-pulse light passes through optical demultiplexer 103 and optical variable delay device 4, and is then sent via optical demultiplexer 104 to synchronization processing unit 5. In synchronization processing unit 5, the short-pulse light is converted into an electrical signal by a photodetector, for example, a high-speed PD 5a, and sent to PLL 5b, where synchronization processing is performed on the millimeter-wave multi-tone signal generated by calibration signal generation unit 20. The multi-tone signal is sent to electro-optic sampling unit 30, where electro-optic sampling of the millimeter-wave multi-tone signal is performed using the short-pulse light output from the short-pulse light source 2 and branched by an optical brancher (not shown) without passing through variable optical delay device 4.

[0106] In the interferometer 110, CW light is input to a first optical path OP1 that includes the optical variable delay device 4 and a second optical path OP2 that does not include the variable delay device 4, and the CW light output from the first optical path OP1 and the CW light output from the second optical path OP2 interfere with each other and are output as interference light. For example, the CW light output from a CW light source 101 made of a CW laser is split by an optical splitter 102, and one part is sent to an optical splitter 104 and the other part is sent to an optical multiplexer 105. The CW light sent to the optical splitter 104 is sent to the optical splitter 103 through the optical variable delay device 4 in the opposite direction to the short pulse light. The CW light that has passed through the optical variable delay device 4 is sent via the optical splitter 103 to the optical multiplexer 105, where it is multiplexed with the CW light sent from the optical splitter 102 side to generate interference light. That is, the CW light that has passed through the variable optical delay device 4 interferes with the CW light that has not. The intensity of the interference light is detected by the photodetector 106, and the interference signal is sent to the frequency divider 107. The frequency divider 107 divides the interference signal, and the resulting signal is 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 wavelength λ (period) of the CW light. Therefore, the multi-tone signal obtained by electro-optic sampling is sampled at regular intervals relative to the delay amount, regardless of the sweep speed of the variable optical delay device 4. This makes it possible to correct phase fluctuations in the millimeter-wave multi-tone signal resulting from instability in the sweep speed of the variable optical delay device 4.

[0107] (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 downconverter (a frequency conversion unit 72, an intermediate frequency signal conversion unit 73) of a millimeter waveband signal measurement unit 70 that measures a signal under measurement by frequency converting (downconverting) it. To this end, 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 that corrects the delay amount caused by the optical variable delay unit 4.

[0108] The millimeter waveband signal measuring unit 70, short pulse light source 2, and variable optical delay unit 4 of this embodiment correspond to the signal measuring unit, pulse light source, and variable delay unit of the present invention, respectively, and the three-tone intermediate frequency signal generating unit 10 and reference signal modulating unit 17 of this embodiment correspond to the multi-tone intermediate frequency signal generating unit of the present invention.

[0109] The short pulse light source 2 outputs short pulse light P1 at a predetermined repetition rate. Specifically, for example, a mode-locked fiber laser is used to generate short pulse light P1 with a repetition rate of 100 MHz and a pulse width of approximately 100 fs. The short pulse light P1 output from the short pulse light source 2 is branched by the optical branching device 3 into two short pulse lights P2 and P3. The short pulse light P2 is input to the optical variable delay device 4 via the optical demultiplexer 103, and the short pulse light P3 is input to the synchronization processing unit 5.

[0110] The variable optical delay device 4 continuously changes the delay time of 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 demultiplexer 104.

[0111] In this embodiment, the optical variable delay device 4 is disposed between the optical branching device 3 and the electro-optic sampling unit 30, but is not limited to this arrangement. The optical variable delay device 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 optical variable delay device 4 may be placed between the optical branching device 3 and the synchronization processing unit 5.

[0112] When the switches SW11 and SW12 are set to the lower position in FIG. 5, the calibration signal generating unit 20 generates a CW local oscillator signal S 22 is used to generate the modulated multi-tone intermediate frequency signal S 19 is up-converted to the millimeter wave frequency to generate the calibration signal S 20 To this end, 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.

[0113] 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 Output as

[0114] The reference signal generator 18 of the reference signal modulation unit 17 receives the reference synchronization signal S from the reference synchronization signal generator 16. 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 is the reference signal S 18 and modulates the modulated multi-tone intermediate frequency signal S 19 is output to the frequency conversion unit 21. 16 may or may not be synchronized with the repetition frequency of the short pulse light source 2.

[0115] 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 band frequency using the local signal generator 22 and the frequency converter 21 to generate the calibration signal S 20 When the switches SW1 and SW2 are set to the upper position in FIG. 5, the calibration signal S 20 The phase difference is measured.

[0116] The synchronization processing unit 5 generates a multi-tone intermediate frequency signal S 10 and local oscillator signal S 22 and the repetition frequency of the short pulse light source 2, a millimeter wave band 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 branching unit 3 and outputs the calibration signal S 20 are converted into the intermediate frequency signals S1 to S3 and the local oscillator signal S4 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 oscillating amplifier.

[0117] 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 oscillator signal S 22 The voltage controlled oscillators (VCOs) in the local signal generating unit 22 and 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.

[0118] The calibration signal S is obtained 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.

[0119] The electro-optic sampling unit 30 outputs the calibration signal S 20 is applied to the electro-optic crystal 31, and linearly polarized short pulse light P4 from the optical variable 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 photodetector 33 via the polarization separator 32. When an electric field is applied to the electro-optic crystal 31, the polarization of the light reflected 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 photodetector 33 to generate an electrical signal S 30 The electrical signal S output from the photodetector 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.

[0120] The pulse width of the short pulse light P1 is calculated as 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 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 signal is recorded, the millimeter-wave calibration signal S 20 The time waveform can be measured.

[0121] Generally, 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 unit 17 is provided in the calibration signal generation unit 20 to generate a reference signal S 18 The lock-in detector 40 is provided after the electro-optic sampling unit 30 to generate a reference signal S 41 Lock-in detection is performed using a

[0122] The reference signal generator 18 of the reference signal modulation unit 17 receives the reference synchronization signal S from the reference synchronization signal generator 16. 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 is the reference signal S 18 and modulates the modulated multi-tone intermediate frequency signal S 19 is output to the frequency conversion unit 21. 16 may or may not be synchronized with the repetition frequency of the short pulse light source 2.

[0123] The output signal S from the reference signal modulation unit 17 19 is up-converted to a millimeter wave band frequency using the local signal generator 22 and the frequency converter 21 to generate the calibration signal S 20 When the switches SW1 and SW2 are set to the upper position in FIG. 5, the calibration signal S 20 The phase difference is measured.

[0124] 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 from the reference synchronization signal generator 16. 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 and 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 is the reference signal S 42 and a low-pass filter 45 extracts the low-frequency components.

[0125] Generally, the cutoff frequency of the low-pass filter 45 is set to a value equal to the cutoff frequency of 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 S and is determined by the sweep speed of the optical variable delay device 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 Fig. 1. If the cutoff frequency of the low-pass filter 45 is lowered, the sweep speed of the optical variable delay 4 must be slowed down, which takes time for measurement, but the frequency band is narrowed and the S / N ratio is improved.

[0126] Normally, the phase detection sections 51a to 51c of the three-tone phase difference measurement section 50 at the subsequent stage have frequency selectivity to detect 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 the S / N ratio of the phase measurement is determined by the latter.

[0127] Therefore, the low-pass filter 45 of the lock-in detection unit 40 may 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 unit 50 as in this embodiment, or when the sampling rate is lowered to reduce the amount of calculation in the phase detection units 51a to 51c.

[0128] 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 influence of DC drift and 1 / f noise of the photodetector 33 of the electro-optic sampling unit 30 can be avoided, and the measurement sensitivity can be improved even if the measurement bands of the phase detection units 51a to 51c are the same.

[0129] 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 into 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.

[0130] The three-tone phase difference measurement unit 50 detects the phase of each tone by digital signal processing and calculates the phase difference. Specifically, the phase detection unit 51a of the three-tone phase difference measurement unit 50 detects the phase of the electrical signal S from the electro-optic sampling unit 30. 30 The phase of the first tone of the three tones in the signal generators 11a to 11c is detected. Similarly, phase detectors 51b and 51c detect the phases of the second and third tones, respectively. Here, the phase difference between the sine waves generated by intermediate frequency signal generators 11a to 11c may be corrected.

[0131] Generally, in the 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 process is carried out as the calibration signal S 20 The frequency of these three tones is changed and repeated to measure the second derivative of the phase over a predetermined frequency range. The frequency characteristics of the phase can be obtained by integrating the second derivative of the phase twice. The phase difference measurement result S 50 is output from the phase difference calculation unit 52.

[0132] 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 millimeter wave band signal measuring unit 70 is used to measure the calibration signal S 20 The phase difference is measured.

[0133] In the millimeter wave band signal measurement unit 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 oscillator signal S 71 The synchronization processing unit 5 may control 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 for converting the signal into a second intermediate frequency signal, an orthogonal frequency converter for converting the signal into an I / Q signal, an A / D converter for converting the signal into a digital signal, etc.

[0134] 5, and the switches SW3 and SW4 are set to the upper position in FIG. 5. The millimeter wave band signal measuring unit 70 is used to measure the calibration signal S 20 5, the switches SW11 and SW12 are set to the upper position so that modulation is not performed in the reference signal modulation unit 17, and a path is set to bypass the electro-optic sampling unit 30, the lock-in detection unit 40, and the A / D converter 111.

[0135] 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 previous section, the phase detectors 51a to 51c detect the phases of the three tones, and the phase difference calculator 52 calculates the second order differential of the phases of the three tones, and the calibration signal S 20 The frequency of the three tones is changed and repeated, and the second-order differential of the phase is integrated twice to obtain the frequency characteristic of the phase. 50' will be output.

[0136] [Delay correction section] Next, the delay amount correcting unit 100 will be described.

[0137] 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 optical variable delay unit 4, and as shown in FIG. 5, includes CW light source 101, interferometer 110, photodetector 106, frequency divider 107, and multi-tone signal sampling unit 120.

[0138] The CW light source 101 is, for example, a semiconductor laser, and is configured to generate CW light of a predetermined wavelength.

[0139] The interferometer 110 is configured such that CW light is input to a first optical path OP1 that includes an optical variable delay device 4 and a second optical path OP2 that does not include an optical variable delay device 4, and causes the CW light output from the first optical path OP1 and the CW light output from the second optical path OP2 to interfere with each other and output as interference light.

[0140] Specifically, the interferometer 110 includes an optical demultiplexer 102, an optical demultiplexer 103 such as a half mirror, an optical demultiplexer 104 such as a half mirror, and an optical multiplexer 105. The optical demultiplexer 102 is provided at the branch point of the first optical path OP1 and the second optical path OP2, and demultiplexes the CW light output from the CW light source 101 into a first CW light and a second CW light. The optical demultiplexer 104 is provided on the first optical path OP1, and receives the first CW light and the short pulse light sent from the short pulse light source 2 via the optical demultiplexer 3 and the optical variable delay device 4. The optical demultiplexer 104 outputs the first CW light to the first optical path OP1 and outputs the short pulse light toward the electro-optic sampling unit 30. The optical demultiplexer 103 is provided on the first optical path OP1 on the opposite side of the optical demultiplexer 104 with the optical variable delay device 4 in between, and outputs the first CW light that has passed through the optical variable delay device 4 on the first optical path OP1 to the optical multiplexer 105, and outputs short pulse light to the optical variable delay device 4. The optical multiplexer 105 is provided at the junction of the first optical path OP1 and the second optical path OP2, and multiplexes the first CW light output by the optical demultiplexer 103 with the second CW light demultiplexed by the optical demultiplexer 102 to generate interference light. 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.

[0141] The photodetector 106 includes, for example, a low-speed photodiode, and 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 between the first optical path and the second optical path (the delay time of the optical variable delay device 4) is equal to an integer multiple of the wavelength (period) of the CW light.

[0142] The frequency divider 107 divides the frequency of the interference signal output from the photodetector 106. If the division ratio of the frequency divider 107 is N (N is an integer), then a rectangular wave is output from the frequency divider 107, where the optical path length difference between the first optical path and the second optical path (the delay time of the optical variable delay device 4) rises every N times the wavelength (period) of the CW light.

[0143] 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 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.

[0144] With this configuration, the multi-tone signal obtained by electro-optic sampling is sampled at regular intervals relative to the delay amount, regardless of the sweep speed of the variable optical delay device 4. Since the frequency of the CW light is about three orders of magnitude higher than the frequency of the millimeter-wave multi-tone signal, if a CW laser or other device with a relatively stable wavelength is used as the CW light source 101, it is possible to correct 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. For example, when correcting a delay amount of 1 ns with a CW light wavelength of 1.5 μm, if the wavelength drift is 5 pm or less, the phase drift at 300 GHz will be 0.4° or less. Note that a CW laser with a stable wavelength can be relatively easily realized using a wavelength locker or the like.

[0145] [Division ratio / Oversampling ratio] The frequency of the interference signal is the frequency of the CW light multiplied by the sweep rate of the optical variable delay 4, and the frequency of the multi-tone signal obtained by electro-optic sampling is the frequency of the millimeter-wave signal multiplied by the sweep rate of the optical variable delay 4. Because the frequency of the CW light is about three orders of magnitude higher than the frequency of the millimeter-wave signal, the frequency of the interference signal is also about three orders of magnitude higher than the frequency of the multi-tone signal obtained by electro-optic sampling. If the interference signal were used directly as the A / D conversion clock, the sampling frequency would be higher than necessary, requiring a high-speed A / D converter and large-capacity memory. Therefore, by appropriately setting the division ratio of frequency divider 107 and using the output of frequency divider 107 as the A / D conversion clock, a necessary and sufficient sampling frequency can be obtained.

[0146] The division ratio of the frequency divider 107 is N, and the frequency of the CW light is f cw , 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 CW / 2rf rf (1) where f rf uses the highest tone frequency of the millimeter-wave tone signal. When r=1, it is 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) in the lock-in detection unit 40.

[0147] For example, if the wavelength of the CW 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 1 / 161th of that required when the interference signal is used directly as the A / D conversion clock can be used.

[0148] [Problems with constructing an interferometer using optical fiber] Generally, when an optical fiber is used as part of the interferometer 110, the delay time changes due to temperature changes in the optical fiber, which in turn changes the phase of the CW light, thereby changing the phase of the interference signal. Therefore, it is preferable to set the phase change rate of the CW light due to the sweep of the optical variable delay 4 (the minimum rate, since fluctuations are assumed) to be greater than the maximum rate of phase change of the CW light due to temperature changes in the optical fiber. In other words, it is preferable to set the sweep rate of the optical variable delay 4 to be greater than the maximum rate of phase change of the CW light due to temperature changes in the optical fiber. This ensures that even if phase changes occur due to temperature changes in the optical fiber, the phase change of the interference signal is always unidirectional, allowing the phase change of the interference signal to be accurately acquired with a single optical receiver 106. Because the frequency of the CW light is about three orders of magnitude higher than the frequency of the millimeter-wave signal, the phase change of the corrected multi-tone signal caused by the phase change of the CW light is about three orders of magnitude smaller than the phase change of the CW light. Regarding the phase change of the CW light due to temperature change, if the interferometer 110 is operated with the optical variable delay device 4 stopped and the optical path difference kept constant, it is possible to observe the interference signal peaking or dropping to zero due to changes in the optical path length caused by temperature changes, and this makes it possible to determine the extent of the phase change of the CW light due to temperature changes. In addition, if the length of the optical fiber and the temperature change are known, the phase change of the CW light due to temperature changes can be calculated.

[0149] However, if the interferometer 110 is constructed in free space such as in air, such a problem does not occur. 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 not use optical fiber for the optical path but to set the optical path in free space such as in air.

[0150] [Problem of mixing CW light and pulsed light] 24 to 27, the first CW light that has passed through the optical variable delay device 4 is input to the electro-optic sampling unit 30 via the optical demultiplexer 104, but even if the CW light is input to the electro-optic sampling unit 30, it only measures the DC component of the electric field and does not affect the measurement of the millimeter-wave signal.

[0151] In the conventional configurations of Figures 24 to 27, the short pulse light passes through the optical variable delay device 4 and enters the photodetector 106 of the interferometer 110 via the optical demultiplexer 104 and the optical multiplexer 105. However, if the frequency of the interference signal from the interferometer 110 is set to be lower than the repetition frequency of the short pulse light, the repetition frequency of the short pulse light and its harmonic components can be removed by using a slow photodetector 106 or providing a low-pass filter.

[0152] Even if CW light is input to the electro-optic sampling unit 30 or short-pulse light is input to the photodetector 106 of the delay amount correction unit 100, there is basically no effect. However, in practice, there may be effects such as noise. Therefore, it is desirable to have a configuration in which the CW light and short-pulse light are optically separated and input to the photodetector 106 and the electro-optic sampling unit 30, respectively. 5, even when a half mirror is used for the optical demultiplexer 104, the CW light is output from the optical demultiplexer 104 in the left and upper directions in the figure, and is therefore not input to the electro-optic sampling unit 30. Furthermore, even when a half mirror is used for the optical demultiplexer 103, the short pulse light is output from the optical demultiplexer in the right and upper directions in the figure, and is therefore not input to the photodetector 106. In this way, by making the propagation direction of the short pulse light input to the optical variable delay device 4 and the propagation direction of the CW light input to the first optical path OP1 opposite to each other, it becomes possible to optically separate the CW light and the short pulse light and input them to the photodetector 106 and the electro-optic sampling unit 30, respectively, even when a cost-effective optical component such as a half mirror is used.

[0153] <Variation 1> Another example of the configuration of the interferometer will be described with reference to FIG.

[0154] The interferometer 110A in FIG. 6 includes an optical demultiplexer 102 provided at the branch point of the first optical path OP1 and the second optical path OP2, an optical multiplexer 105 provided at the junction point of the first optical path OP1 and the second optical path OP2, and a polarizing beam splitter 103A and a second polarizing beam splitter 104A on either side of the optical variable delay device 4 on the first optical path OP1.

[0155] The optical path provided in the first optical path OP1 between the second polarizing beam splitter 104A and the polarizing beam splitter 103A is a shared optical path through which both short pulse light and CW light pass. The polarizing beam splitter 103A receives the short pulse light sent via the optical branching device and outputs the short pulse light to the variable optical delay device 4 provided in the first optical path. The second polarizing beam splitter 104A receives the short pulse light that has passed through the variable optical delay device and outputs the short pulse light to the electro-optic sampling unit.

[0156] Specifically, the optical demultiplexer 102 is provided at the branch point between the first optical path OP1 and the second optical path OP2, and demultiplexes the CW light output from the CW light source 101 into a first CW light and a second CW light. The second polarizing beam splitter 104A is provided on the first optical path OP1, and receives the first CW light of a first polarization (s-polarized light) and the short pulse light of a second polarization (p-polarized light) orthogonal to the first polarization (s-polarized light) sent via the optical variable delay device 4 from different paths, and outputs the first CW light of the first polarization (s-polarized light) in the opposite direction to the short pulse light of the second polarization (p-polarized light), i.e., along the first optical path OP1 toward the optical variable delay device 4. More specifically, the second polarizing beam splitter 104A receives the s-polarized first CW light and the p-polarized short-pulse light from directions that are 90 degrees apart, reflects the s-polarized first CW light, and transmits the p-polarized short-pulse light.

[0157] The polarizing beam splitter 103A is provided on the first optical path OP1 on the opposite side of the second polarizing beam splitter 104A across the optical variable delay device 4, and separates the first CW light of the first polarization (s-polarized) that has passed through the optical variable delay device 4 on the first optical path OP1 from the short pulse light of the second polarization (p-polarized) that has passed through the optical branching device 3. Specifically, the polarizing beam splitter 103A receives the s-polarized first CW light and the p-polarized short pulse light from directions that are 180 degrees apart, reflects the s-polarized first CW light, and transmits the p-polarized short pulse light. The optical multiplexer 105 is provided at the junction of the first optical path OP1 and the second optical path OP2, and multiplexes the first CW light separated by the polarizing beam splitter 103A with the second CW light separated by the optical branching device 102 to generate interference light. The photodetector 106 detects the intensity of the interference light and outputs it as an interference signal, and the frequency divider 107 divides the frequency of the interference signal.

[0158] In this embodiment, the first polarization is s-polarized light and the second polarization is p-polarized light, but this is not limited to this, and it is sufficient if the CW light and the short pulse light can be combined or separated depending on the polarization state, and for example, the first polarization may be p-polarized light and the second polarization may be s-polarized light.

[0159] With the above-described configuration, the phase characteristic calibration device according to this embodiment optically separates the CW light and the short pulse light based on their polarization state and propagation direction, and these are input to the photodetector 106 and the electro-optic sampling unit 30, which are connected to the interferometer 110a. This makes it possible to suppress the effects of noise and other phenomena caused by mixing of the CW light and the short pulse light. Furthermore, the reflection and transmission of s-polarized light and p-polarized light by the polarizing beam splitter 103A and the second polarizing beam splitter 104A makes it possible to reflect and transmit the first CW light and the short pulse light without any theoretical loss, allowing more power to be input to the electro-optic crystal 31 of the electro-optic sampling unit 30 and the photodetector 106.

[0160] Although CW light and short pulse light can be multiplexed and separated by polarization as in this modified example, reflection and transmission can also be performed using a wavelength filter or the like. Specifically, if the CW light and short pulse light are set to different wavelengths and a wavelength filter that reflects the CW light wavelength and transmits the short pulse light wavelength is installed in place of polarizing beam splitter 103A and second polarizing beam splitter 104A, it is possible to separate and multiplex CW light and short pulse light without any theoretical loss, as in this modified example. Conversely, it is also possible to separate and multiplex CW light and short pulse light without any theoretical loss by using a wavelength filter that reflects the short pulse light wavelength and transmits the CW light wavelength.

[0161] Furthermore, the interferometer 110A of the modified example shown in FIG. 6 can be used not only in the first embodiment but also as an interferometer in the phase characteristic calibration devices of the second to eighth embodiments described later.

[0162] <Variation 2> Another example of the configuration of the interferometer will be described with reference to FIG.

[0163] The interferometer 110B in FIG. 14 includes an optical demultiplexer 102 provided at the branch point of the first optical path OP1 and the second optical path OP2, an optical multiplexer 105 provided at the junction of the first optical path OP1 and the second optical path OP2, and a first polarizing beam splitter 104B and a second polarizing beam splitter 103B on either side of the optical variable delay device 4 on the first optical path OP1.

[0164] The optical path provided in the first optical path OP1 between the first polarizing beam splitter 104B and the second polarizing beam splitter 103B is a shared optical path through which the short pulse light and the CW light pass in opposite directions. That is, at the first polarizing beam splitter 104B, the CW light enters the shared optical path and travels in the forward direction, and at the second polarizing beam splitter 103B, the short pulse light enters the shared optical path and travels in the reverse direction.

[0165] Specifically, the optical demultiplexer 102 is provided at the branch point between the first optical path OP1 and the second optical path OP2, and demultiplexes the s-polarized CW light as a first polarization output from the CW light source 101 into a first CW light and a second CW light. The first polarizing beam splitter 104B is provided on the first optical path OP1, and receives the s-polarized first CW light and p-polarized short pulse light as a second polarization orthogonal to the first polarization, which is sent in the reverse direction along the first optical path OP1 from the pulse light source 2 via the optical variable delay device 4, via different paths. The first polarizing beam splitter 104B outputs the s-polarized first CW light in the forward direction along the first optical path OP1 and outputs the p-polarized short pulse light toward the electro-optic sampling unit 30. More specifically, the first polarizing beam splitter 104B receives the s-polarized first CW light and the p-polarized short-pulse light from directions that are 90 degrees apart, reflects the s-polarized first CW light, and transmits the p-polarized short-pulse light.

[0166] The second polarizing beam splitter 103B is provided on the first optical path OP1 on the opposite side from the first polarizing beam splitter, with the optical variable delay device 4 sandwiched therebetween, and receives the s-polarized first CW light that has passed through the optical variable delay device 4 and the 45°-inclined linearly polarized short pulse light output from the short pulse light source 2 from different paths, outputs the first CW light in the forward direction of the first optical path OP1, and outputs the p-polarized short pulse light in the reverse direction of the first optical path OP1. Specifically, the short pulse light and the first CW light are input to the second polarizing beam splitter 103B from directions that are 180° different from each other, and the second polarizing beam splitter 103B reflects the s-polarized first CW light and transmits the p-polarized short pulse light. Optical multiplexer 105 is provided at the junction of first optical path OP1 and second optical path OP2, and generates interference light by multiplexing the s-polarized first CW light output by second polarizing beam splitter 103B and the s-polarized second CW light separated by optical splitter 102. Photoreceiver 106 detects the intensity of the interference light and outputs it as an interference signal, and frequency divider 107 divides the frequency of the interference signal.

[0167] The s-polarized short-pulse light separated from the linearly polarized short-pulse light tilted at 45° by the second polarizing beam splitter 103B is input to the synchronization processing unit 5. Therefore, the second polarizing beam splitter 103B also serves as the optical branching device 3 of the first modification of FIG.

[0168] With the above configuration, the s-polarized first CW light and the p-polarized short pulse light propagate in opposite directions in the first optical path OP1 including the optical variable delay device 4, resulting in a large extinction ratio in the separation. Specifically, even if the polarization extinction ratio of the first polarizing beam splitter 104B is poor, only a portion of the first CW light passes through the first polarizing beam splitter 104B and does not enter the electro-optic sampling unit. Therefore, the extinction ratio in the separation of the pulse light and the CW light is large. Furthermore, compared to the basic configuration shown in FIG. 6, the optical branching device 3 in FIG. 6 is not required, resulting in a simpler configuration.

[0169] Moreover, by changing the ratio between the s-polarized component and the p-polarized component of the short-pulse light input to the second polarizing beam splitter 103B, the demultiplexing ratio can be changed as needed, and therefore the optical power of the short-pulse light can be used efficiently.

[0170] <Variation 3> Another example of the configuration of the interferometer will be described with reference to FIG.

[0171] The interferometer 110C in FIG. 15 includes a polarizing beam splitter / combiner 104C provided at the branch point of the first optical path OP1 and the second optical path OP2, an optical directional coupler 103C provided at the junction of the first optical path OP1 and the second optical path OP2, and a half-wave plate 108 provided on the second optical path OP2.

[0172] The optical path provided in the first optical path OP1 between the polarizing beam splitter / combiner 104C and the optical directional coupler 103C is a shared optical path through which the short pulse light and the CW light pass in opposite directions. That is, at the polarizing beam splitter / combiner 104C, the CW light enters the shared optical path and travels in the forward direction, and at the optical directional coupler 103C, the short pulse light enters the shared optical path and travels in the reverse direction.

[0173] Specifically, the polarization beam splitter / combiner 104C is provided at the branch point of the first optical path OP1 and the second optical path OP2, and receives, via different paths, the 45° inclined polarized CW light output from the CW light source 101 and the p-polarized short-pulse light sent from the short-pulse light source 2 via the variable optical delay 4 in the reverse direction of the first optical path OP1, outputs the s-polarized first CW light as the first polarization in the forward direction of the first optical path OP1 toward the variable optical delay 4, outputs the p-polarized second CW light to the second optical path OP2, and outputs the p-polarized short-pulse light toward the electro-optic sampling unit 30. More specifically, polarized CW light inclined at 45 degrees from directions different by 90 degrees, p-polarized short-pulse light, and s-polarized short-pulse light are input to the polarizing beam splitter / combiner 104C, which reflects the first s-polarized CW light, transmits the second p-polarized CW light, transmits the p-polarized short-pulse light, and reflects the s-polarized short-pulse light.

[0174] The half-wave plate 108 is provided on the second optical path OP2 and converts the p-polarized second CW light output from the polarizing beam splitter / combiner 104C to the second optical path OP2 into s-polarized light.

[0175] The optical directional coupler 103C is provided at the junction of the first optical path OP1 and the second optical path OP2. The optical directional coupler 103C combines the s-polarized first CW light from the first optical path OP1 with the s-polarized second CW light from the second optical path OP2 to generate interference light, and outputs p-polarized short pulse light in the reverse direction of the first optical path OP1 toward the optical variable delay device 4. Specifically, the optical directional coupler 103C reflects a predetermined proportion of the input light and transmits a predetermined proportion of the input light. Therefore, the short pulse light reflected by the optical directional coupler 103C is output toward the second optical path, converted to s-polarized light by the half-wave plate 108, and input to the polarizing beam splitter / combiner 104C. The short pulse light output from the polarizing beam splitter / combiner 104C is input to the electro-optic sampling unit. The short pulse light that does not pass through the variable optical delay device 4 is input to the electro-optic sampling unit, but because it samples the millimeter-wave electric field applied to the electro-optic crystal at a fixed time, it becomes a DC component and does not adversely affect the measurement of the millimeter-wave electric field using the short pulse light that has passed through the variable optical delay device 4. The photoreceiver 106 detects the intensity of the interference light and outputs it as an interference signal, and the frequency divider 107 divides the frequency of the interference signal.

[0176] With the above configuration, the phase characteristic calibration device according to this embodiment is configured so that the s-polarized first CW light and the p-polarized short pulse light propagate in opposite directions in the first optical path OP1 including the optical variable delay device 4, resulting in a large extinction ratio in the separation. Specifically, the polarizing beam splitter / combiner 104C only separates the CW light into the first and second optical paths, and does not output it toward the electro-optic sampling unit. Furthermore, the optical directional coupler only separates the short pulse light into the first and second optical paths, and does not output it toward the photodetector 106. Therefore, the extinction ratio in the separation of the pulse light and the CW light is large.

[0177] Furthermore, a half-wave plate 108 is provided in the second optical path OP2, and converts the p-polarized second CW light output from the polarizing beam splitter / combiner 104C to the second optical path OP2 into s-polarized light. With this configuration, the phase characteristic calibration device of this embodiment does not require the optical demultiplexer 102 and optical multiplexer 105 in FIG. 6, thereby simplifying the configuration compared to the basic configuration shown in FIG. 6. Furthermore, even if the angle of linearly polarized light changes in the optical variable delay device 4, performance can be easily maintained by adjusting the angle of linearly polarized light by changing the principal axis direction of the half-wave plate 108.

[0178] As described above, the phase characteristic calibration device according to this embodiment uses fewer optical elements than the basic configuration shown in FIG. 6, and only CW light is incident on the optical receiver 106, so that the influence of noise can be suppressed.

[0179] <Variation 4> Another example of the configuration of the interferometer will be described with reference to FIG.

[0180] The interferometer 110D in FIG. 16 includes a first polarizing beam splitter 104D provided at the branch point of the first optical path OP1 and the second optical path OP2, an optical multiplexer 105 provided at the junction of the first optical path OP1 and the second optical path OP2, a second polarizing beam splitter 103D provided on the opposite side of the first polarizing beam splitter 104D across the optical variable delay device 4 in the first optical path OP1, and a half-wave plate 108 provided on the second optical path OP2.

[0181] The optical path provided in the first optical path OP1 between the first polarizing beam splitter 104D and the second polarizing beam splitter 103D is a shared optical path through which the short pulse light and the CW light pass in opposite directions. That is, at the first polarizing beam splitter 104D, the CW light enters the shared optical path and travels in the forward direction, and at the second polarizing beam splitter 103D, the short pulse light enters the shared optical path and travels in the reverse direction.

[0182] Specifically, the first polarizing beam splitter 104D is provided at the branch point of the first optical path OP1 and the second optical path OP2, and receives, via different paths, the 45° inclined polarized CW light output from the CW light source 101 and the p-polarized short-pulse light sent from the short-pulse light source 2 via the optical variable delay device 4 in the reverse direction of the first optical path OP1, outputs the s-polarized first CW light as the first polarization in the forward direction of the first optical path OP1 toward the optical variable delay device 4, outputs the p-polarized second CW light as the second polarization to the second optical path OP2, and outputs the p-polarized short-pulse light toward the electro-optic sampling unit 30. More specifically, the short-pulse light and the CW light are input to the first polarizing beam splitter 104D at angles that differ by 90 degrees from each other, and the first polarizing beam splitter 104D reflects the s-polarized first CW light, transmits the p-polarized second CW light, and transmits the p-polarized short-pulse light.

[0183] The half-wave plate 108 is provided on the second optical path OP2 and converts the p-polarized second CW light output from the first polarizing beam splitter 104D to the second optical path OP2 into s-polarized light.

[0184] The second polarizing beam splitter 103D is provided on the first optical path OP1 on the opposite side from the first polarizing beam splitter, with the optical variable delay device 4 sandwiched therebetween, and receives the s-polarized first CW light that has passed through the optical variable delay device 4 and the polarized short-pulse light output from the short-pulse light source 2 and tilted at 45° from different paths, outputs the s-polarized first CW light in the forward direction of the first optical path OP1, outputs the p-polarized short-pulse light in the reverse direction of the first optical path OP1 toward the optical variable delay device 4, and outputs the s-polarized short-pulse light toward the synchronization processing unit 5. Specifically, the short-pulse light and the first CW light are input to the second polarizing beam splitter 103D from directions that are 180 degrees different from each other, and the second polarizing beam splitter 103D reflects the s-polarized input light and transmits the p-polarized input light. Optical multiplexer 105 is provided at the junction of the first optical path and the second optical path, and multiplexes the first CW light and the second CW light to generate interference light, which is output to optical receiver 106. Optical receiver 106 detects the intensity of the interference light and outputs it as an interference signal, and frequency divider 107 divides the frequency of the interference signal.

[0185] With the above configuration, the phase characteristic calibration device according to this embodiment can efficiently output short pulse light toward the electro-optic sampling unit and efficiently output CW light toward the photodetector 106 because the second polarizing beam splitter 103D and the first polarizing beam splitter 104D separate short pulse light and CW light without any theoretical loss. Furthermore, the first optical path OP1 including the optical variable delay device 4 is configured so that the s-polarized CW light and the p-polarized short pulse light propagate in opposite directions, resulting in a large extinction ratio in the separation. Specifically, the first polarizing beam splitter 104D only splits the CW light into the first and second optical paths and does not output it toward the electro-optic sampling unit. Furthermore, even if the polarization extinction ratio of the second polarizing beam splitter 103D is poor, only a portion of the first CW light passes through the polarizing beam splitter 103D and does not enter the synchronization processing unit. Therefore, the extinction ratio in the separation of the pulse light and the CW light is large.

[0186] Furthermore, a half-wave plate 108 is provided on the second optical path OP2, and converts the p-polarized second CW light output from the first polarizing beam splitter 104D to the second optical path OP2 into s-polarized light. With this configuration, the phase characteristic calibration device according to this embodiment does not require the optical demultiplexer 102 of FIG. 6, and the configuration is simpler than the basic configuration shown in FIG.

[0187] 6 corresponds to the second polarizing beam splitter 103D, and the s-polarized short-pulse light separated from the linearly polarized short-pulse light tilted at 45° by the second polarizing beam splitter 103D is input to the synchronization processing unit 5. With this configuration, the optical splitter 3 in FIG. 6 is not required, and the configuration is simpler than the basic configuration shown in FIG.

[0188] Furthermore, by changing the ratio between the s-polarized component and the p-polarized component of the short-pulse light input to the second polarizing beam splitter 103D, the demultiplexing ratio can be changed as needed, thereby enabling efficient use of the optical power of the short-pulse light.

[0189] As described above, compared to the basic configuration shown in FIG. 6, the phase characteristic calibration device according to this embodiment uses fewer optical elements, has less pulse loss, can input more power to the electro-optic crystal, can change the demultiplexing ratio by changing the polarization of the short pulse light, can use optical power efficiently, and has a large extinction ratio because the CW light and the short pulse light travel in different directions.

[0190] <Variation 5> Another example of the configuration of the interferometer will be described with reference to FIG.

[0191] 17 differs from the second modification shown in FIG. 14 in that the optical multiplexer 105 is an optical multiplexer / demultiplexer 105E, and the optical receiver 106 is a differential optical receiver 109. The other configurations are the same as those of the second modification, and the same components are denoted by the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0192] The optical multiplexer / demultiplexer 105E receives the s-polarized first CW light separated by the second polarizing beam splitter 103B, reflects a predetermined percentage of the input light, and transmits a predetermined percentage of the input light. The optical multiplexer / demultiplexer 105E also receives the s-polarized second CW light separated by the optical demultiplexer 102, reflects a predetermined percentage of the input light, and transmits a predetermined percentage of the input light. The transmitted s-polarized first CW light and the reflected s-polarized second CW light are combined to generate first interference light IL1. The reflected s-polarized first CW light and the transmitted s-polarized second CW light are combined to generate second interference light IL2. The first interference light IL1 and the second interference light IL2 are reflected and transmitted in opposite directions by the optical multiplexer / demultiplexer 105E, resulting in complementary interference. The differential photodetector 109 receives the first interference light IL1 and the second interference light IL2, differentially detects the intensities of the interference lights, and outputs an interference signal. The frequency divider 107 divides the interference signal to an appropriate frequency.

[0193] With this configuration, the phase characteristic calibration device according to this embodiment can remove common-mode noise, increase the strength of the interference signal, and improve the S / N ratio, in addition to the effects of Modification 2 in FIG.

[0194] <Variation 6> Another example of the configuration of the interferometer will be described with reference to FIG.

[0195] An interferometer 110F in Fig. 18 differs from the third modification shown in Fig. 15 in that a polarizing beam splitter 3F is used instead of the optical branching device 3, and the photodetector 106 is a differential photodetector 109. The other configurations are the same as those in the third modification, and the same components are denoted by the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0196] Optical directional coupler 103C receives a first CW light and transmits a predetermined percentage of it and reflects a predetermined percentage, and also receives a second CW light and transmits a predetermined percentage of it and reflects a predetermined percentage. Thus, the transmitted light of the first CW light and the reflected light of the second CW light generate first interference light IL1, and the reflected light of the first CW light and the transmitted light of the second CW light generate second interference light IL2. The first interference light IL1 is input to a differential photodetector 109 via a polarizing beam splitter 3F, and the second interference light IL2 is input to the differential photodetector 109. The first interference light IL1 and the second interference light IL2 are reflected and transmitted in opposite directions by the optical directional coupler 103C, resulting in complementary interference. The differential photodetector 109 receives the first interference light IL1 and the second interference light IL2, differentially detects the intensities of the interference lights, and outputs an interference signal. The frequency divider 107 divides the interference signal to an appropriate frequency.

[0197] With this configuration, the phase characteristic calibration device according to this embodiment can remove common-mode noise, increase the intensity of the interference signal, and improve the S / N ratio, in addition to the effects of Modification 3 in Fig. 15. Furthermore, by replacing the optical branching device 3 in Modification 3 in Fig. 15 with the polarizing beam splitter 3F, the problem of CW light entering the short pulse light source 2 is resolved compared to Modification 3.

[0198] <Variation 7> Another example of the configuration of the interferometer will be described with reference to FIG.

[0199] Interferometer 110G in Fig. 19 differs from Modification 4 shown in Fig. 16 in that optical multiplexer 105 is an optical multiplexer / demultiplexer 105G, and photodetector 106 is a differential photodetector 109. The other configurations are the same as those in Modification 4, and the same components are denoted by the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

[0200] The optical multiplexer / demultiplexer 105G receives the s-polarized first CW light split by the second polarizing beam splitter 103D, reflects a predetermined percentage of the input light, and transmits a predetermined percentage of the input light. The optical multiplexer / demultiplexer 105G also receives the s-polarized second CW light that has passed through the half-wave plate 108, reflects a predetermined percentage of the input light, and transmits a predetermined percentage of the input light. The transmitted s-polarized first CW light and the reflected s-polarized second CW light are combined to generate first interference light IL1. The reflected s-polarized first CW light and the transmitted s-polarized second CW light are combined to generate second interference light IL2. The first interference light IL1 and the second interference light IL2 are reflected and transmitted in opposite directions by the optical multiplexer / demultiplexer 105G, resulting in complementary interference. The differential photodetector 109 receives the first interference light IL1 and the second interference light IL2, differentially detects the intensities of the interference lights, and outputs an interference signal. The frequency divider 107 divides the interference signal to an appropriate frequency.

[0201] With this configuration, the phase characteristic calibration device according to this embodiment can remove common-mode noise, increase the strength of the interference signal, and improve the S / N ratio, in addition to the effects of Modification 4 in FIG.

[0202] In the above-mentioned modifications 1 to 7, the first polarized light is s-polarized light and the second polarized light is p-polarized light, but this is not limiting and any other suitable polarization may be used as long as the CW light and the short pulse light can be combined or separated depending on the polarization state. For example, the first polarized light may be p-polarized light and the second polarized light may be s-polarized light. Furthermore, in the above-mentioned modifications 2 to 7, the light is not limited to linearly polarized light tilted at 45°, but may have both s-polarized and p-polarized components. Therefore, linearly polarized light or elliptically polarized light may be set to have any tilt angle depending on the power ratio (branching ratio) to be separated.

[0203] As in the above-mentioned modifications 1 to 7, CW light and short pulse light can be multiplexed or demultiplexed by polarization, but multiplexing or demultiplexing can also be performed using a wavelength filter, etc. CW light and short pulse light can also be multiplexed or demultiplexed using a simple half mirror.

[0204] Moreover, the interferometers of the above-described modified examples 1 to 7 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.

[0205] [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 measurement unit 70 will be described.

[0206] Here, the frequency response is expressed as a complex number A·e containing amplitude A and phase θ. jθ It can be used to calibrate both the phase frequency characteristic and the amplitude and phase frequency characteristics. 20 The frequency characteristics (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 characteristics (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 (f) is found, and G(f) can be found using the following formula. G(f)=Y c (ff LO ) / X c (f) (2) where f LOis the local oscillator frequency of the millimeter wave band signal measuring unit 70.

[0207] 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 .

[0208] 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), the measurement result X(f) 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 can be found using the following equation. X(f)=Y(ff LO ) / G(f) (3)

[0209] Switches SW3 and SW4 are set to the lower position in FIG. 5, and the signal S under test from the millimeter wave band signal transmitter 60 is 60 is 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 result 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.

[0210] <Effects> The phase characteristic calibration device 1 of this embodiment, which simultaneously performs electro-optic sampling and acquires an interference signal, has the advantage of being able to correct unpredictable random fluctuations in the sweep speed of the variable optical delay device 4, such as mechanical "backlash." Furthermore, because the short-pulse light used for electro-optic sampling and the CW light used for the interferometer 110 pass through the same optical path within the variable optical delay device 4, the effects of deformation due to temperature changes and the like are the same for both, making it possible to accurately correct this effect. For example, in a method of correcting the sweep speed by separately installing 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 changes, making it difficult to accurately correct the sweep speed of the variable optical delay device 4.

[0211] (Second embodiment) Next, a phase characteristic calibration apparatus 1A according to a second embodiment of the present invention will be described with reference to FIG.

[0212] The phase characteristic calibration apparatus 1A according to this embodiment differs from that of the first embodiment in the configuration of the multi-tone signal sampling unit 120A. The other configurations are the same as those of the first embodiment, and the same components are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0213] As shown in FIG. 7 , multi-tone signal sampling unit 120A includes A / D converter 111 that converts the multi-tone signal output from lock-in detection unit 40 into a digital signal, low-pass filter 112 that blocks harmonic components of the rectangular wave output from frequency divider 107 and converts it into a sine wave, second A / D converter 113 that performs A / D conversion on the output signal of low-pass filter 112, and 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.

[0214] 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.

[0215] When detecting the timing of equal phase intervals from a sine wave signal obtained by dividing the interference signal and passing it through a low-pass filter, the phase cannot be uniquely determined using only a sine wave, so a Hilbert transform is performed to create sine waves and cosine waves 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, making it possible to accurately detect equal phase intervals.

[0216] In the resampling method, the sampling frequency of the resampling can be changed by changing the phase interval detected by equal phase interval detection unit 115, so the division ratio does not necessarily have to satisfy the oversampling ratio r≧1 in equation (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.

[0217] 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 frequency of the interference signal, the multi-tone signal obtained by electro-optic sampling can be resampled at intervals that are constant 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.

[0218] (Third embodiment) Next, a phase characteristic calibration apparatus 1B according to a third embodiment of the present invention will be described with reference to FIG.

[0219] The phase characteristic calibration apparatus 1B according to this embodiment differs from the first embodiment in the configurations of a calibration signal generation unit 20B, a multi-tone signal separation unit 40B, a multi-tone signal sampling unit 120B, and a multi-tone phase difference measurement unit 50B. The other configurations are the same as those of the first embodiment, and the same components are denoted by the same reference numerals, and detailed descriptions thereof will be omitted where appropriate.

[0220] When the switch SW10 is set to the upper position in the figure, the calibration signal generating unit 20B generates a local oscillator signal S 22 is used to generate the multi-tone intermediate frequency signal S 10 is up-converted to the calibration signal S 20 To this end, the calibration signal generating section 20 includes a multi-tone intermediate frequency signal generating and reference signal modulating section 10B, a local oscillator signal generating section 22, and a frequency converting section 21.

[0221] The multi-tone intermediate frequency signal generating and reference signal modulating unit 10B generates multi-tone signals (intermediate frequency signals) S1 to S4 of 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 that differ 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 and reference signal modulating unit 10B generates intermediate frequency signals S1 to S4 with different frequencies, and modulates and combines the intermediate frequency signals with reference signals S5 and S7 with different frequencies or orthogonal reference signals S6 and S8 with the same frequency as the reference signals but with a phase difference of 90 degrees. 10In this embodiment, an example of generating a four-tone signal is shown. Reference signal S5 and reference signal S7, reference signal S5 and orthogonal reference signal S8, reference signal S7 and orthogonal reference signal S6, and orthogonal reference signal S6 and orthogonal reference signal S8 are orthogonal because they have different frequencies, while reference signal S5 and orthogonal reference signal S6, and reference signal S7 and orthogonal reference signal S8 are orthogonal because they have the same frequency but a phase difference of 90 degrees. Therefore, reference signals S5, S7 and orthogonal reference signals S6, S8 are orthogonal to each other in all combinations.

[0222] More specifically, the multi-tone intermediate frequency signal generating and reference signal modulating unit 10B includes intermediate frequency signal generators 11a to 11d, reference signal generators 12a and 12b, 90-degree phase shifters 14a and 14b, modulators 13a to 13d, an adder 15, and a reference synchronization signal generator 16.

[0223] 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 with different frequencies and a predetermined phase difference. Normally, a sine wave is used, but any repetitive signal with a desired frequency component may also be used. As will be described later, to simplify the phase measurement data processing, it is desirable to set the frequencies of the intermediate frequency signals S1 to S4 at a fixed frequency interval according to the frequency resolution of the phase measurement.

[0224] The reference signal generator 12a receives the reference synchronization signal S from the 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.

[0225] The reference signal generator 12b has a frequency different from that of the reference signal S5 and is the same as 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.

[0226] Reference signals S5, S7 and orthogonal reference signals S6, S8 may be unipolar signals with a voltage above zero 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 reference signals S5, S7 and orthogonal reference signals S6, S8 are repetitive signals other than sine waves, such as rectangular waves, harmonic components that are integer multiples of the fundamental frequency will exist, so it is advisable to set the frequencies of both signals so that, for example, an integer multiple of the frequency of reference signal S5 does not match the frequency of reference signal S7.

[0227] 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 Output as

[0228] 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 the multi-tone intermediate frequency signal S 10 It may be output as:

[0229] Here, one reference synchronization signal S 16 The reference signal S5 and the reference signal S7 are generated in synchronization with the reference sync signal S 16A and the reference synchronization signal S 16B The reference signal S5 is the reference synchronization signal S 16A and the reference signal S7 is synchronized with the reference synchronization signal S 16B It may be configured to synchronize with the

[0230] The calibration signal generator 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 generate the calibration signal S 20 The frequency converter 21 extracts either the upper sideband wave or the lower sideband wave after the mixer and outputs the local oscillator signal S 22 A filter to remove leakage of the signal may be included. The following example shows the case where the upper sideband wave is used in frequency conversion. When the lower sideband wave is used, the frequency relationship is different, but this method can be applied in the same way.

[0231] The local signal generator 22 or the frequency converter 21 receives the local signal S 22 A frequency multiplier may be included to multiply the frequency of the local oscillator signal S 22 This is interpreted as the frequency of

[0232] The synchronization processing unit 5 synchronizes the intermediate frequency signals S1 to S4 with the local oscillator signal S 22 and the repetition frequency of the short pulse light source 2, a millimeter wave band 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 branching unit 3 and outputs the calibration signal S 20 are converted into the intermediate frequency signals S1 to S4 and the local oscillator signal S 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 oscillating amplifier.

[0233] More specifically, the synchronization processing unit 5 uses a phase-locked loop (PLL) circuit to synchronize the local oscillator signal S 22and the frequency 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 unit 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.

[0234] In addition, the reference synchronization signal S 16 may 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 and 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. In this way, the calibration signal S (excluding the modulation by the reference signals S5 and S7 and the orthogonal reference signals S6 and S8) 20 The repetition frequency of this pulse is an integer multiple of the repetition frequency of the short pulse light source 2.

[0235] The calibration signal S is obtained using the electro-optic sampling unit 30. 20 When measuring the phase difference between the calibration signal S 20 is applied to the electro-optic crystal 31, and the short pulse light P4 from the optical variable 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 photodetector 33 via the polarization separator 32. When an electric field is applied to the electro-optic crystal 31, the polarization of the light reflected 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 photodetector 33 to output an electrical signal S 30 Output as

[0236] The pulse width of the short pulse light P4 is calculated as the calibration signal S 20If 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 is sampled at the repetition period of the short pulse light P4. The repetition period of the short pulse light source 2 is the same as the calibration signal S (excluding 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 modulation by the reference signals S5 and S7 and the orthogonal reference signals S6 and S8) 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 the signal S is recorded, the millimeter-wave calibration signal S is recorded by the low-speed photodetector 33. 20 The time waveform can be measured.

[0237] Specifically, the electrical signal S from the electro-optic sampling unit 30 30 is the calibration signal S 20 is obtained by multiplying the time axis of the time waveform of the signal S 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 1 ps to 1 s. In terms of frequency, the calibration signal S of the 300 GHz millimeter wave band 20 can be converted into a low frequency signal of 0.3 Hz and measured.

[0238] The electrical signal S from the electro-optic sampling unit 30 30 is input to the multi-tone signal separator 40.

[0239] The multi-tone signal separator 40B separates the calibration signal S 20 and the short pulse light P4 while changing the relative time difference between the electrical signal S 30 and a sine wave S with the same frequency as the reference signals S5 and S7 and a predetermined phase difference 42 ,S 44Or 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 30 The multi-tone signal separator 40 is configured to separate tone signals corresponding to three or more intermediate frequency signals S1 to S4 (four in the embodiment of FIG. 8) included in the sine wave S. To this end, the multi-tone signal separator 40 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. 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 90 degree phase difference. 42 ~S 45 are orthogonal to each other in all combinations.

[0240] The reference signal generator 41a receives the reference synchronization signal S from the reference synchronization signal generator 16. 17 According to the above, the reference signal S5 is a sine wave having the same frequency as the reference signal S5. 40 Here, the reference synchronization signal S 17 is usually the reference synchronization signal S 16 However, it is not limited to this, and may be, for example, a signal of the same frequency as the reference synchronization signal S 17 is the reference synchronization 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.

[0241] The phase shifter 42a converts the calibration signal S sampled by the electro-optic sampling unit 30 into a phase signal S20 The phase of the reference signal S5 in 40 The reference signal S 40 and adjust the phase of the reference signal S 42 Here, the phase shifter 42a outputs the reference signal S 40 The order of the reference signal generator 41a and the phase shifter 42a is reversed 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 reference signal S5 may be generated at a low frequency and the calibration signal S 20 and the reference synchronization signal S 17 If the phase difference due to the difference in propagation delay time can be ignored, the phase shifter 42a may be omitted.

[0242] The modulator 44a receives the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 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 modulates the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 42 and a reference signal S 43 and the low-frequency components are extracted by a low-pass filter 45b.

[0243] The reference signal generator 41b receives the reference synchronization signal S from the reference synchronization signal generator 16. 17 According to the above, the reference signal S7 is a sine wave having the same frequency as the reference signal S7. 41 occurs.

[0244] The phase shifter 42b converts the calibration signal S sampled by the electro-optic sampling unit 30 into a phase signal S 20 The phase of the reference signal S7 in 41 The reference signal S 41 and adjust the phase of the reference signal S 44 Here, the phase shifter 42b outputs the reference signal S41 The order of the reference signal generator 41b and the phase shifter 42b is reversed to adjust the phase of the reference synchronization signal S 17 and the phase of the reference signal S 44 Alternatively, the frequency of the reference signal S7 may be low and the calibration signal S 20 and the reference synchronization signal S 17 If the phase difference due to the difference in propagation delay time can be ignored, the phase shifter 42b may be omitted.

[0245] The modulator 44c receives the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 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 modulates the electrical signal S from the electro-optic sampling unit 30. 30 is the reference signal S 44 and a reference signal S 45 and the low-frequency components are extracted by a low-pass filter 45d.

[0246] Here, the reference synchronization signal S 16 ,S 17 According to the reference signal S5, the reference signal S7, and the reference signal S 40 and the reference signal S 41 However, if reference signal generators A and B are provided to generate sine waves with different frequencies, the output signal of reference signal generator A is used as reference signal S5 and reference signal S6. 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:

[0247] With the above configuration, the electrical signal S 30 The four tones are separated.

[0248] In the following, the calibration signal S 20 The angular frequency of each of the four tones is ω RF1,ω RF2 ,ω RF3 ,ω RF4 ,each phase is φ1,φ2,φ3,φ4, and the reference signal S 40 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.

[0249] Generally, the low-pass filters 45a to 45d are configured to 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 so that the low-pass filters 45a to 45d pass through, it is possible to separate the individual tones. Lowering the cutoff frequency of the low-pass filters 45a to 45d requires slowing down the sweep speed of the optical variable delay 4, which increases the measurement time, but narrows the measurement frequency band and improves the signal-to-noise ratio.

[0250] Note that the phase detection units 51a-51d of the subsequent multi-tone phase difference measurement unit 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 units 51a-51d narrower than the band of the low-pass filters 45a-45d of the multi-tone signal separation unit 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 unit 40B can be set to an appropriate cutoff frequency as an anti-aliasing filter when A / D conversion is performed before the multi-tone phase difference measurement unit 50B as in this embodiment, or when the sampling rate is lowered to reduce the amount of calculation in the phase detection units 51a-51d.

[0251] In addition, the electrical signal S from the electro-optic sampling unit 30 30 In this case, the angular frequency of the sampled four-tone signal is Rω RF1 ,Rω RF3 ,Rω RF2 ,RωRF4 Instead, the angular frequency ω modulated by the reference signal S5 and the reference signal S7 r1 ±Rω RF1 ,ω r1 ±Rω RF3 ,ω r2 ±Rω RF2 ,ω r2 ±Rω RF4 To detect the components of, for example, ω r1 and ω r2 By setting this to several MHz, signals with a frequency of several MHz can be measured, making it possible to avoid DC drift and 1 / f noise in the photodetector 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 high sensitivity.

[0252] Furthermore, because each tone signal is separated in the multi-tone signal separation unit 40, 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, and this makes it possible to measure the phase characteristics by narrowing the frequency interval without increasing the size of the variable optical delay device 4.

[0253] Furthermore, 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

[0254] In addition, electrical components such as high-frequency mixers and amplifiers generally have nonlinear distortion, and when two sine waves of 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 The reference signal S7 is a sine wave of frequency f r2 are sine waves, modulation of each tone by reference signal S5 or reference signal S7 generates an upper sideband and a lower sideband.

[0255] This calibration signal S 20 When 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 The 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 causes f RF3 2F from r2 +f r1 The spectrum occurs at distant frequencies, and the third-order intermodulation between the upper sideband of the first tone and the upper sideband of the second tone causes f RF3 2F from r2 -f r1 Similarly, the spectrum is generated at distant frequencies. 20 A spectrum of third-order intermodulation distortion occurs around the first to fourth tones.

[0256] In this way, a total of 24 spectra due to third-order intermodulation distortion are generated near the first to fourth tones, but they do not overlap with either the upper or lower sidebands of the first to fourth tones. r2 - 2nd floor r1 If the bandwidth is set narrower than |, the spectrum due to third-order intermodulation distortion will be outside the band of low-pass filters 45a to 45d in multi-tone signal separation section 40 or outside the measurement band of phase detection sections 51a to 51d. Therefore, accurate phase measurement becomes possible without being affected by third-order intermodulation distortion.

[0257] The phase detector 51a of the multi-tone phase difference measuring unit 50B detects the electrical signal S from the electro-optic sampling unit 30. 30 The first tone of the four tones in RF1 ) to detect the phase.

[0258] Phase detection unit 51a is implemented by digital calculations that input the corrected multi-tone signal obtained by A / D converter 111a of multi-tone signal sampling unit 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 unit 51a may input the corrected multi-tone signal obtained by A / D converter 111a of multi-tone signal sampling unit 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.

[0259] Similarly, the phase detectors 51c, 51b, and 51d detect the electrical signal S from the electro-optic sampling unit 30. 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 difference between the intermediate frequency signals S1 to S4 generated by the intermediate frequency signal generators 11a to 11d.

[0260] Generally, when measuring the phase 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 the phase of each of the four tones and outputs it as the phase difference measurement result from the electro-optic sampling unit 30. Calculating the second derivative requires the phases of three tones, and the second derivative of the phase at two frequencies can be calculated from the phases of the four tones. Similarly, the second derivative of the phase at the N-2 frequency point can be calculated from the phases of N tones, so this method can be extended to any number of tones greater than three.

[0261] This process is used as the calibration signal S 20The 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 way, the phase difference measurement result S 50 is output from the phase difference calculation unit 52.

[0262] The millimeter wave band signal measuring unit 70 measures the calibration signal S 20 8, and switches SW3 and SW4 are set to the upper side of the figure. Multi-tone intermediate frequency signal generating section 25 includes intermediate frequency signal generators 26a to 26d and adder 27, and adds four intermediate frequency signals S 11 ~S 14 are combined by an adder 27 to obtain a multi-tone intermediate frequency signal S 15 The multi-tone intermediate frequency signal S 15 is sent to the frequency conversion unit 21 via the switch SW10, and is converted into a millimeter-wave calibration signal S 20 The calibration signal S 20 is input to the millimeter wave band signal measuring unit 70 via switches SW1 and SW3.

[0263] The intermediate frequency signal conversion unit 73 may include a second frequency converter that converts the frequency of the intermediate frequency signal output from the frequency conversion unit 72 again, a quadrature frequency converter that converts the intermediate frequency (IF) signal into an in-phase (I) signal and a quadrature (Q) signal, an A / D converter that converts into a digital signal, etc. When the intermediate frequency signal conversion unit 73 includes frequency conversion, the local oscillator signal S 71The local frequency of the millimeter wave band signal measuring unit 70 is interpreted as including not only the frequency of the intermediate frequency signal converter 73 but also the local frequency of the intermediate frequency signal converter 73. The frequency converter 72 of this embodiment and the intermediate frequency signal converter 73 in the case where frequency conversion is included correspond to the downconverter of the present invention. The intermediate frequency signal converter 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 measuring unit 50B or the phase correction unit 74.

[0264] The output signal S from the intermediate frequency signal conversion unit 73 of the millimeter wave band signal measurement unit 70 70 are input to phase detectors 51a to 51d of multi-tone phase difference measurement unit 50B via switches SW21 to SW24. Phase detectors 51a to 51d of multi-tone phase difference measurement unit 50B detect the phases of the four tones, and phase difference calculation unit 52 calculates the second-order differential of each phase of the four tones to generate 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 value of the phase is integrated twice to obtain the frequency characteristic of the phase. 50' is output as

[0265] 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.

[0266] [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 response 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 frequency characteristics of the phase and the calibration of the frequency characteristics of both the amplitude and phase.

[0267] The amplitude frequency characteristic is A·e jθ The real part of the function is x and the imaginary part is y. The arctangent function tan-1 Absolute value (x) instead of (y / x) 2 +y 2 ) 1 / 2 Alternatively, it may be measured by a spectrum analyzer separate from the phase characteristic calibration apparatus 1B, or may be measured by a power meter separate from the phase characteristic calibration apparatus 1B using a CW signal.

[0268] Calibration signal S 20 is input to the electro-optic sampling unit 30, the electrical signal S 30 The frequency characteristics (complex number) of X c (f EO ), 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 characteristics (complex number) of Y c (f IF ), and the frequency characteristics (complex numbers) of the frequency conversion units 72 and 73 of the millimeter wave band signal measurement unit 70 are expressed as G(f RF ) where f EO is the electrical signal S sampled by the electro-optic sampling unit 30. 30 frequency, f IF is the signal S converted in frequency by the millimeter wave band signal measuring unit 70. 70 frequency, f RF is the calibration signal S 20 and millimeter wave signal S 60 is the frequency.

[0269] As described above, the switches SW10, SW1, SW21, SW22, SW23, and SW24 in FIG. 8 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 ) is obtained. Also, the switches SW10, SW1, SW21, SW22, SW23, and SW24 are set to the lower side of the figure, and the switches SW3 and SW4 are set to the upper side of 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 ) (4)

[0270] where f LO is 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 calculating unit 55 calculates G(f RF ) and outputs it to the phase correction unit 74 of the millimeter wave band signal measurement unit 70.

[0271] Signal under test S 60 The frequency characteristics (complex number) of X(f RF ), switches SW3 and SW4 are set to the lower position in the figure, 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' The frequency characteristics (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 ) (5)

[0272] Therefore, the output signal S from the intermediate frequency signal conversion unit 73 of the millimeter wave band signal measurement unit 70 70' In contrast, the local frequency f LO The frequency is shifted by 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.

[0273] For example, the inverse H(f IF )=1 / G(f IF +f LO ) to calculate the time domain impulse response at the intermediate frequency of the millimeter wave band signal measuring unit 70, and by configuring an FIR digital filter with the impulse response as a coefficient in the phase correction unit 74, it is 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 on the intermediate frequency (IF) signal to 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.

[0274] The millimeter wave band signal transmitting section 60 is made up of, for example, an intermediate frequency signal generating section 61, a local oscillator signal generating section 62, and a frequency converting section 63. When the switches SW3 and SW4 in FIG. 8 are set to the lower side, the signal S under test 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 measurement results 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.

[0275] (Fourth embodiment) Next, a phase characteristic calibration apparatus 1C according to a fourth embodiment of the present invention will be described with reference to FIG.

[0276] The phase characteristic calibration apparatus 1C according to this embodiment differs from that of the third embodiment in the configuration of the multi-tone signal sampling unit 120C. The other configuration is the same as that of the third embodiment, and the same components are denoted by the same reference numerals and detailed description thereof will be omitted as appropriate.

[0277] Specifically, as shown in FIG. 9 , 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, 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 signals obtained by dividing the frequency of the interference signal, and resamples the digital signals obtained by A / D converters 111a, 111b, 111c, and 111d at the detected equal phase intervals.

[0278] 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.

[0279] With the above configuration, each tone signal is resampled at equal phase intervals of the output signal of frequency divider 107, which divides the interference signal, so that each tone signal obtained by electro-optic sampling unit 30 and multi-tone signal separation unit 40B can be sampled at constant intervals relative to the delay amount, regardless of the sweep speed of variable optical delay unit 4. This makes it possible to correct phase fluctuations in the signal obtained by electro-optic sampling that result from instability in the sweep speed of variable optical delay unit 4. Furthermore, as with the second embodiment, the frequency division ratio does not necessarily have to satisfy the oversampling ratio r≧1 in equation (1), and it is also possible to set the frequency division ratio so that A / D converters 111a to 111d and 113 operate at the same sampling frequency.

[0280] (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.

[0281] The phase characteristic calibration device 1D according to this embodiment receives a measurement intermediate frequency signal S 81 is frequency converted (up-converted) to generate 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 modulated by the reference signal is output as 19 is up-converted by the local signal generator 83 and 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 millimeter wave band signal S is generated. The other configurations are the same as those of the first embodiment, and the same components are denoted by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate. 80 The millimeter wave band 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.

[0282] As shown in FIG. 10, 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 the three-tone intermediate frequency signal S 10 is the reference signal S 18 Multi-tone intermediate frequency signal S modulated by 19 When the switches SW6 and SW7 are set to the upper position 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 as a calibration signal. 80 Then, the millimeter wave signal S 80 is input to the electro-optic sampling unit 30.

[0283] Next, a method for calibrating the phase frequency characteristics of the frequency conversion section 84 of the millimeter wave band signal generation section 80 will be described.

[0284] In the configuration shown in FIG. 10, the multi-tone intermediate frequency signal S output from the reference signal modulation unit 17 19 The frequency characteristics (complex number) of X c1 (f IF1 ), and the frequency characteristic (complex number) of the frequency conversion unit 84 of the millimeter wave band 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 generation unit 80 80 is input to the electro-optic sampling unit 30, the electrical signal S 30 The frequency characteristics (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 measurement signal S 80' frequency, f EO is the electrical signal S sampled by the electro-optic sampling unit 30. 30 is the frequency.

[0285] X c1 (f IF1 ) is the multi-tone intermediate frequency signal S generated by the three-tone intermediate frequency signal generating unit 10 and the reference signal modulating unit 17. 19 10. The frequency characteristics of the millimeter-wave band signal S output from the frequency converter 84 of the millimeter-wave band signal generator 80 are known. 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 ) (6) where f LO1 is the local signal S of the millimeter wave band signal generator 80 83is the frequency of the optical variable delay device 4, and R is the sweep rate (the amount of change in delay time per unit time) of the optical variable delay device 4.

[0286] 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: one is to correct it in the phase correction unit 82 of the millimeter wave band signal generation unit 80, and the other is to correct the frequency characteristics by arranging a phase correction unit after the intermediate frequency signal conversion unit 93 of the millimeter wave band signal reception unit 90. Figure 10 shows the former case.

[0287] 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 wave band signal generating unit 80, and the signal from the intermediate frequency signal generating unit 81 of the millimeter wave band signal generating unit 80 is passed through an FIR digital filter using the impulse response as a coefficient.

[0288] In the latter case, the inverse H2(f IF2 )=1 / G1(f IF2 +f LO2 ) is subjected to an inverse Fourier transform 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 frequency, f LO2 is the local signal S of the millimeter wave band signal receiving unit 90 91 The millimeter wave band signal receiving unit 90 is made up 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 of LO2 is the local oscillator signal S 91This is interpreted as including the local frequency of the intermediate frequency signal conversion unit 93 in addition to the frequency of the signal.

[0289] 10, and an arbitrary intermediate frequency signal S output from the intermediate frequency signal generating section 81 of the 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 wave band signal receiving unit 90, whereby the frequency characteristics of the frequency conversion unit 84 are corrected to produce a measurement signal S 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 is up-converted by the local signal generator 83 and the frequency converter 84 to generate a measurement signal with no phase correction, which is input to the millimeter wave band signal receiver 90, and the signal output from the intermediate frequency signal converter 93 is subjected to phase correction, thereby generating a measurement signal S 80' The millimeter wave band signal receiving unit 90, which is the measurement target, can obtain a result equivalent to that when the millimeter wave band signal is received by the millimeter wave band signal receiving unit 90.

[0290] 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 wave band signal receiving unit 90 may be analyzed to display the error vector magnitude (EVM) or the like.

[0291] (Sixth embodiment) Next, a phase characteristic calibration apparatus 1E according to a sixth embodiment of the present invention will be described with reference to FIG.

[0292] The 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 generation / reference signal modulation section 10B, a multi-tone signal separation section 40B, a multi-tone signal sampling section 120B, and a multi-tone phase difference measurement section 50B. The other configurations are the same as those of the fifth embodiment, and the same components are designated by the same reference numerals, and detailed descriptions thereof will be omitted where appropriate.

[0293] Specifically, as shown in FIG. 11, the multi-tone intermediate frequency signal generating and 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 position 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 as a calibration signal. 80 Then, the millimeter wave signal S 80 is input to the electro-optic sampling unit 30.

[0294] The configurations of multi-tone signal separation section 40B, multi-tone signal sampling section 120B, and multi-tone phase difference measurement section 50B are the same as those in the third embodiment. Furthermore, the method of calibrating the phase characteristics of up-converter 84 of millimeter waveband signal generation section 80 is the same as that in the fifth embodiment.

[0295] With the above configuration, the phase characteristic calibration device 1E according to this embodiment uses the calibration signal S 80is input to the electro-optic sampling unit 30, separated into individual tone signals by the multi-tone signal separation unit 40B, and their phases measured by the 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 due to instability in the sweep speed of the optical variable delay unit 4 and the like can be reduced, thereby improving the S / N ratio.

[0296] (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. 12. The phase characteristic calibration apparatus 1F according to this embodiment differs from the fifth embodiment (Fig. 10) in the configuration of a multi-tone signal sampling section 120A, but the other configuration is the same as that of the fifth embodiment. The same configuration is assigned the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0297] The configuration of multi-tone signal sampling unit 120A is the same as that of the second embodiment (FIG. 7). As shown in FIG. 12, multi-tone signal sampling unit 120A includes A / D converter 111 that converts the multi-tone signal output from lock-in detection unit 40 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, second A / D converter 113 that performs A / D conversion on the output signal of low-pass filter 112, and 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.

[0298] Furthermore, the method for 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.

[0299] With the above-described configuration, the phase characteristic calibration device 1F according to the seventh embodiment uses the millimeter wave band signal S as a calibration signal in order 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.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. When this is done, each tone signal is resampled according to a signal obtained by dividing the frequency of the interference signal. This reduces fluctuations in the phase of each tone signal due to instability in the sweep speed of the optical variable delay unit 4, etc., and improves the S / N ratio, thereby enabling the accuracy of phase characteristic calibration to be improved.

[0300] (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. 13. The phase characteristic calibration device 1G according to this embodiment differs from the sixth embodiment (Fig. 11) in the configuration of a multi-tone signal sampling unit 120C, but the other configuration is the same as that of the sixth embodiment. The same configuration is assigned the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0301] The configuration of multi-tone signal sampling unit 120C is the same as that of the fourth embodiment (FIG. 9). As shown in FIG. 13, 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 to a sine wave, 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 signals obtained by dividing the frequency of the interference signal, and resamples the digital signals obtained by A / D converters 111a, 111b, 111c, and 111d at the detected equal phase intervals.

[0302] The method for 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.

[0303] With the above-described configuration, the phase characteristic calibration device 1G according to the eighth embodiment uses the millimeter wave band signal S as a calibration signal in order 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. 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 phases are 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, fluctuations in the phase of each tone signal due to instability in the sweep speed of the optical variable delay unit 4 and the like can be reduced, improving the S / N ratio and thereby improving the accuracy of phase characteristic calibration. [Industrial Applicability]

[0304] As described above, the present invention has the effect of improving the performance of separating pulsed light and CW light using cost-effective optical components without complicating the optical system, and is useful in phase characteristic calibration devices and phase characteristic calibration methods in general. [Explanation of symbols]

[0305] 1, 1A, 1B, 1C, 1D, 1E, 1G Phase characteristic calibration equipment 2. Short pulse light source (pulse light source) 3 Optical splitter 4, 204 Optical variable delay (variable delay) 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-optic sampling unit 31 Electro-optic crystal 32 Polarization separation unit 33 Receiver 40 Lock-in detection unit 40B Multi-tone signal separator (lock-in detector) 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 units 52 Phase difference calculation section 55 Phase correction value calculation unit 60 Millimeter wave band 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 band 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 103A, 103B, 103D, 104A, 104B, 104D, 3F Polarizing Beam Splitters 104C Polarizing Beam Splitter / Combiner 103C Directional coupler 105G optical multiplexer / demultiplexer 106 Receiver 107 Frequency divider 108 Half-wave plate 109 Differential receiver 110, 110A, 110B, 110C, 110D, 110E, 110F, 110G 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 Multi-tone signal sampling section 130, 130C Resampling processing section

Claims

1. a pulsed light source (2) that generates pulsed light at a predetermined repetition frequency; an optical branching device (3) that branches the pulsed light; a calibration signal generation unit (20) including a multi-tone intermediate frequency signal generation unit (10, 17) that combines three or more intermediate frequency signals of different frequencies and outputs a multi-tone intermediate frequency signal modulated with a reference signal, and that up-converts the multi-tone intermediate frequency signal using a local oscillator signal of a predetermined frequency and a frequency conversion unit (21) to generate a calibration signal; a synchronization processing unit (5) that 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 oscillator 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 unit, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay (4) to which one or the other of the pulsed lights output from the optical branching device 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) 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 multi-tone signals corresponding to the three or more intermediate frequency signals included in the electrical signal; a CW light source (101) that generates CW light of a predetermined wavelength; an interferometer (110) in which the 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 which 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 output them as interference light; a photodetector (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 the output of the frequency divider and outputs it as a corrected multi-tone signal; a multi-tone phase difference measuring unit (50) that detects phase differences 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 characteristics of the phase of the downconverters (72, 73) of the signal measurement unit (70) from the phase difference between the tone signals; A phase characteristic calibration device (1; 1A) for calibrating the phase frequency characteristic of the down converter of the signal measurement unit that down-converts and measures a signal under test, The interferometer is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other.

2. a pulsed light source (2) that generates pulsed light at a predetermined repetition frequency; an optical branching device (3) that branches 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) that 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 oscillator 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 unit, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay (4) to which one or the other of the pulsed lights output from the optical branching device 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) 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; a CW light source (101) that generates CW light of a predetermined wavelength; an interferometer (110) in which the 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 which 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 output them as interference light; a photodetector (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 the 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 characteristics of the phase of the downconverters (72, 73) of the signal measurement unit (70) from the phase difference between the tone signals; A phase characteristic calibration device (1B; 1C) for calibrating the phase frequency characteristic of the down converter of the signal measurement unit that down-converts and measures a signal under test, The interferometer is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other.

3. a pulsed light source (2) that generates pulsed light at a predetermined repetition frequency; an optical branching device (3) that branches the pulsed 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 with a reference signal; a signal generating section (80) that 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) that 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 oscillator 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 unit, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay (4) to which one or the other of the pulsed lights output from the optical branching device 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) 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 multi-tone signals corresponding to the three or more intermediate frequency signals included in the electrical signal; a CW light source (101) that generates CW light of a predetermined wavelength; an interferometer (110) in which the 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 which 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 output them as interference light; a photodetector (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 the output of the frequency divider and outputs it as a corrected multi-tone signal; a multi-tone phase difference measuring unit (50) that detects phase differences 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 characteristics of the phase of the up-converter of the signal generation unit from the phase difference between the tone signals; A phase characteristic calibration device (1D; 1F) comprising: The interferometer is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other.

4. a pulsed light source (2) that generates pulsed light at a predetermined repetition frequency; an optical branching device (3) that branches the pulsed light; a multi-tone intermediate frequency signal generating unit (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; a signal generating section (80) that 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) that 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 oscillator 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 unit, samples the calibration signal in accordance with the pulsed light, and outputs the sampled signal as an electrical signal; a variable delay (4) to which one or the other of the pulsed lights output from the optical branching device 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) 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; a CW light source (101) that generates CW light of a predetermined wavelength; an interferometer (110) in which the 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 which 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 output them as interference light; a photodetector (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 the 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 characteristics of the phase of the up-converter of the signal generation unit from the phase difference between the tone signals; A phase characteristic calibration device (1E; 1G) comprising: The interferometer is characterized in that the propagation direction of the pulsed light input to the variable delay device included in the first optical path and the propagation direction of the CW light input to the first optical path are opposite to each other.

5. The interferometer comprises: an optical demultiplexer (102) provided at a branch point between the first optical path and the second optical path, for demultiplexing the CW light of the first polarization output from the CW light source into a first CW light and a second CW light; a first polarizing beam splitter (104B) provided in the first optical path, receiving the first CW light of the first polarization and the pulsed light of a second polarization orthogonal to the first polarization, which has been sent from the pulse light source through the variable delay device in a reverse direction along the first optical path, via different paths, and outputting the first CW light of the first polarization in a forward direction along the first optical path and outputting the pulsed light of the second polarization toward the electro-optic sampling unit; a second polarizing beam splitter (103B) that is provided on the first optical path on the opposite side to the first polarizing beam splitter side with the variable delay device sandwiched therebetween, and that receives the first CW light of the first polarization that has passed through the variable delay device and the pulsed light that is output from the pulse light source and has polarization components of both the first polarization and the second polarization from different paths, separates the input pulsed light into the pulsed light of the first polarization and the pulsed light of the second polarization, and outputs the first CW light of the first polarization in a forward direction of the first optical path and outputs the pulsed light of the second polarization in a reverse direction of the first optical path toward the variable delay device; an optical multiplexer (105) provided at a junction of the first optical path and the second optical path, which multiplexes the first CW light of the first polarization output by the second polarizing beam splitter and the second CW light of the first polarization separated by the optical demultiplexer to generate the interference light; Equipped with The phase characteristic calibration device according to any one of claims 1 to 4, characterized in that the second polarizing beam splitter also serves as the optical branching device by inputting the pulsed light of the first polarization split by the second polarizing beam splitter into the synchronization processing unit.

6. The interferometer comprises: a polarization beam splitter combiner (104C) provided at a branching point between the first optical path and the second optical path, which receives, via different paths, the CW light output from the CW light source and having polarization components of both the first polarization and a second polarization orthogonal to the first polarization, and the pulsed light of the second polarization sent from the pulsed light source via the variable delay device in the reverse direction of the first optical path, separates the input CW light into a first CW light of the first polarization and a second CW light of the second polarization, outputs the first CW light of the first polarization in the forward direction of the first optical path, outputs the second CW light of the second polarization to the second optical path, and outputs the pulsed light of the second polarization toward the electro-optic sampling unit; a half-wave plate (108) provided in the second optical path, which converts the second CW light of the second polarization output from the polarization beam splitter combiner to the second optical path into the first polarization; an optical directional coupler (103C) provided at a junction of the first optical path and the second optical path, which couples the first CW light of the first polarization with the second CW light of the first polarization to generate the interference light, and which inputs the pulsed light of the second polarization sent from the pulse light source via the optical branching device and outputs the pulsed light in a reverse direction of the first optical path; 5. The phase characteristic calibration device according to claim 1, comprising:

7. The interferometer comprises: a first polarization beam splitter (104D) provided at a branching point between the first optical path and the second optical path, receiving the CW light output from the CW light source and having polarization components of both the first polarization and a second polarization orthogonal to the first polarization, and the pulsed light of the second polarization sent from the pulsed light source via the variable delay device in the reverse direction of the first optical path, from different paths, and separating the input CW light into a first CW light of the first polarization and a second CW light of the second polarization, outputting the first CW light of the first polarization in the forward direction of the first optical path, outputting the second CW light of the second polarization to the second optical path, and outputting the pulsed light of the second polarization toward the electro-optic sampling unit; a half-wave plate (108) provided in the second optical path, which converts the second CW light of the second polarization output from the first polarizing beam splitter to the second optical path into the first polarization; a second polarizing beam splitter (103D) that is provided on the first optical path on the opposite side to the first polarizing beam splitter side with the variable delay device sandwiched therebetween, and that receives the first CW light of the first polarization that has passed through the variable delay device and the pulsed light that is output from the pulse light source and has polarization components of both the first polarization and the second polarization from different paths, separates the input pulsed light into the pulsed light of the first polarization and the pulsed light of the second polarization, and outputs the first CW light of the first polarization in a forward direction of the first optical path and outputs the pulsed light of the second polarization in a reverse direction of the first optical path; an optical combiner (105) provided at a joining point of the first optical path and the second optical path, which combines the first CW light of the first polarization sent from the second polarizing beam splitter and the second CW light of the first polarization sent from the half-wave plate to generate the interference light; Equipped with The phase characteristic calibration device according to any one of claims 1 to 4, characterized in that the second polarizing beam splitter also serves as the optical branching device by inputting the pulsed light of the first polarization split by the second polarizing beam splitter into the synchronization processing unit.

8. 6. The phase characteristic calibration device according to claim 5, wherein the optical multiplexer is an optical multiplexer / demultiplexer (105E) that multiplexes the first CW light separated by the second polarizing beam splitter and the second CW light separated by the optical demultiplexer to generate first interference light and second interference light as the interference light, and the optical receiver is a differential optical receiver (109) that receives the first interference light and the second interference light and differentially detects the intensities of the interference lights.

9. The optical directional coupler combines the first CW light of the first polarization separated by the polarizing beam splitter combiner and the second CW light of the first polarization separated by the polarizing beam splitter combiner and passed through the half-wave plate to generate first interference light of the first polarization and second interference light of the first polarization as the interference light, and a polarizing beam splitter (3F) is used instead of the optical branching device, and the polarizing beam splitter divides the first interference light of the first polarization and the second interference light of the first polarization output from the pulse light source and having polarization components of both the first polarization and the second polarization.

7. The phase characteristic calibration device according to claim 6, wherein the optical receiver is a differential optical receiver (109) that receives the first interference light output from the polarizing beam splitter and the second interference light generated by the optical directional coupler and differentially detects the intensities of the interference lights, and the optical receiver is a differential optical receiver (109) that receives the first interference light output from the polarizing beam splitter and the second interference light generated by the optical directional coupler and differentially detects the intensities of the interference lights.

10. 8. The phase characteristic calibration device according to claim 7, wherein the optical multiplexer is an optical multiplexer / demultiplexer (105G) that multiplexes the first CW light output by the second polarizing beam splitter and the second CW light that has passed through the half-wave plate to generate first interference light and second interference light as the interference light, and the optical receiver is a differential optical receiver (109) that receives the first interference light and the second interference light and differentially detects the intensities of the interference lights.

11. Pulsed light having a predetermined repetition frequency is branched by an optical branching device (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, and a local oscillator signal of a predetermined frequency and a frequency conversion unit (21) are used to up-convert the multi-tone intermediate frequency signal to generate a calibration signal; controlling the frequencies of the three or more intermediate frequency signals and the local oscillator 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 the 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 the relative time difference between the pulsed light used for sampling and the calibration signal by a variable delay device to which one or the other of the pulsed light 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 multi-tone signals corresponding to the three or more intermediate frequency signals contained in the electrical signal; inputting CW light of a predetermined wavelength 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 interference light, detecting the intensity of the interference light as an interference signal, sampling the multi-tone signal in accordance with a signal obtained by dividing the frequency of the interference signal, and generating 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 phase frequency characteristics of the downconverters (72, 73) of the signal measurement unit (70) from the phase difference between the tone signals; a phase characteristic calibration method for calibrating a phase frequency characteristic of the downconverter of the signal measurement unit that downconverts and measures a signal under test, the method comprising: a phase characteristic calibration method, characterized in that, in the output step of the interference light, the pulsed light input to the variable delay device included in the first optical path and the CW light input to the first optical path are propagated in directions opposite to each other.

12. Pulsed light having a predetermined repetition frequency is branched by an optical branching device (3), Three or more intermediate frequency signals having different frequencies are combined, and a multi-tone intermediate frequency signal is generated by modulating the multi-tone intermediate frequency signal with a reference signal. The multi-tone intermediate frequency signal is up-converted by an up-converter (84) of a signal generating unit (80) using a local oscillator signal of a predetermined frequency to generate a calibration signal. using one of the pulsed lights output from the optical branching device to control the frequencies of the three or more intermediate frequency signals and the local oscillator 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; 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 the relative time difference between the pulsed light used for sampling and the calibration signal by a variable delay device to which one or the other of the pulsed light 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 multi-tone signals corresponding to the three or more intermediate frequency signals contained in the electrical signal; inputting CW light of a predetermined wavelength 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 interference light, detecting the intensity of the interference light as an interference signal, sampling the multi-tone signal in accordance with a signal obtained by dividing the frequency of the interference signal, and generating 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 phase frequency characteristic of the up-converter of the signal generating unit that up-converts a measurement intermediate frequency signal and outputs the up-converted signal as a measurement signal, the method comprising: a phase characteristic calibration method, characterized in that, in the output step of the interference light, the pulsed light input to the variable delay device included in the first optical path and the CW light input to the first optical path are propagated in directions opposite to each other.

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