Optical comb generation device

Abstract

A comb generating apparatus is provided for use in optical comb rangefinders and the like to measure distance based on the time difference between the interference signal of the measuring light and the interference signal of the reference light. This apparatus can correct for phase shifts caused by the signal return path other than the measured object, thereby obtaining an absolute distance result with high accuracy. The drive control unit (11) controls the output of M optical comb generators (16A, 16B) in the optical comb generating unit (16) to supply drive signals to cause the M optical comb generators (16A, 16B) to output M (M is an integer of 2 or more) optical combs whose intensity or phase is periodically modulated and whose N (N is an integer of 3 or more) modulation frequencies are cyclically switched and whose modulation frequencies are different from each other.

Description

Technical Field

[0001] This invention relates to an optical comb generating apparatus, such as an optical comb rangefinder, for measuring distance based on the time difference between the interference signal of a measured light and the interference signal of a reference light. This application claims priority based on Japanese Patent Application No. 2021-055640, filed on March 29, 2021, which is incorporated herein by reference. Background Technology

[0002] Conventional active distance measurement methods capable of precise point distance measurement include optical distance measurement using lasers. In laser rangefinders that use lasers to determine the distance to an object, the distance is calculated based on the difference between the laser emission time and the time when the laser light reflected back from the object is detected by a light-receiving element (see, for example, Patent Document 1). Alternatively, for example, modulation of the driving current of a semiconductor laser using a triangular wave or similar modulator is applied, and a photodiode embedded in the semiconductor laser element receives the reflected light from the object. Distance information is obtained based on the dominant wavenumber of the sawtooth wave appearing in the output current of the photodiode.

[0003] Laser rangefinders are known devices for measuring the absolute distance from a point to a measurement point with high precision. For example, Patent Document 1 describes a rangefinder that measures distance based on the time difference between the interference signal of the measurement light and the interference signal of the reference light.

[0004] In the past, it was difficult to achieve a practical absolute distance measuring instrument that could measure long distances with high precision. In order to obtain high resolution, the only method required returning to the origin, such as a laser interferometer, but this method was not suitable for absolute distance measurement.

[0005] The inventors of this case previously proposed an optical comb rangefinder (see, for example, Patent Document 2). This optical comb rangefinder has two optical comb generators that pulse-emit reference light and measurement light, which are interferometrically modulated in intensity or phase and at different modulation frequencies. The interference light between the reference light pulse illuminating the reference surface and the measurement light pulse illuminating the measurement surface is detected by a reference light detector, and the interference light between the reference light pulse reflected from the reference surface and the measurement light pulse reflected from the measurement surface is detected by a measurement light detector. The difference between the distance to the reference surface and the distance to the measurement surface is calculated based on the time difference between the two interference signals obtained by the reference light detector and the measurement light detector, thereby enabling high-precision measurement in a short time.

[0006] In addition, a comb rangefinder has been proposed before (for example, see Patent Document 3): the reference point position for the distance to the measurement surface is specified by a reference optical path, thereby enabling high-precision and short-time long-distance measurement.

[0007] In principle, an optical comb rangefinder uses two optical comb generators driven by two modulation signals of different frequencies to pulse-emit interferometric reference and measurement light pulses. The signal processing unit performs frequency analysis on the interference signals obtained from the reference photodetector (hereinafter referred to as the reference signal) and the measurement photodetector (hereinafter referred to as the measurement signal). The mode number, starting from the center frequency of the optical comb, is designated P. The phase difference between the P modes of the reference signal and the measurement signal is calculated to compensate for the phase difference in the optical comb generation and transmission process from the optical comb generator to the reference point. Then, the phase difference of the signal pulse is determined by calculating the increment of the phase difference on the frequency axis for each pulse, thereby calculating the distance from the reference point to the measurement surface.

[0008] Here, the relative distance measurement speed in the optical comb rangefinder, which uses a pair of modulation signals driven by two optical comb generators with a frequency difference of Δf (e.g., 500 kHz) from the modulation frequencies of the two modulation signals, is determined by the frequency difference Δf of the modulation frequencies. In absolute distance measurement, the absolute distance is calculated by performing multiple distance measurements based on the modulation frequencies of the switching reference and measurement optical pulses.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2001-343234

[0012] Patent Document 2: Japanese Patent No. 5231883

[0013] Patent Document 3: Japanese Patent Application Publication No. 2020-12641 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] In optical comb rangefinders that measure distance based on the time difference between the interference signal of the measuring light and the interference signal of the reference light, distance measurement can theoretically be performed by alternately switching the two modulation signals used to drive the two optical comb generators. However, a problem arises where phase shift caused by the signal return path other than the object being measured becomes a measurement error. Furthermore, the possibility of the object being measured moving at a speed must also be considered.

[0016] In view of the problems mentioned above, the object of the present invention is to provide an optical comb generating apparatus that, in optical comb rangefinders and the like that which measure distance based on the time difference between the interference signal of the measuring light and the interference signal of the reference light, can correct the phase shift caused by the signal transmission path other than the object being measured, thereby obtaining the absolute distance result with high accuracy.

[0017] Another objective of the present invention is to provide an optical comb generating device that can perform high-precision absolute distance measurement for moving bodies that require shorter absolute distance measurement time as their movement speed increases.

[0018] Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the following description of the embodiments.

[0019] Solution for solving the problem

[0020] This invention relates to an optical comb generating device, specifically an optical comb distance measuring device for measuring distance based on the time difference between the interference signal of a measured light and the interference signal of a reference light. The device is characterized by comprising: an optical comb generating unit having M optical comb generators, where M is an integer of 2 or more; and a drive control unit that controls the output of M different drive signals, each with a phase synchronized with a reference frequency signal and N different modulation frequencies, to the M optical comb generators, thereby causing the optical comb generating unit to output M different optical combs, where N is an integer of 3 or more. The optical comb generating unit outputs M different optical combs from the M optical comb generators, each with a periodically modulated intensity or phase and N different modulation frequencies.

[0021] In the optical comb generating apparatus of the present invention, the drive control unit may be configured to include: N signal sources, the N signal sources outputting N modulation signals whose phases are synchronized with the phase of the reference frequency signal and whose modulation frequencies are different from each other; an N-input, M-output switching unit connected to the N signal sources; and a switching control unit controlling the operation of the switching unit to cause the switching unit to output M modulation signals that cyclically switch the N modulation signals and whose modulation frequencies are different from each other, and the optical comb generating apparatus supplies the M modulation signals as drive signals to the M optical comb generators.

[0022] Furthermore, in the optical comb generating apparatus of the present invention, it can be configured such that the N signal sources respectively generate N modulation signals in a state where the phase is synchronized with the phase of the reference frequency signal through a phase-locked loop circuit and the modulation frequency is fixed.

[0023] Furthermore, in the optical comb generating apparatus according to the present invention, the drive control unit may be configured to include: a signal source consisting of M direct digital frequency synthesizers, the direct digital frequency synthesizers operating according to a system clock whose phase is synchronized with the phase of the reference frequency signal; and a switching control unit that controls the operation of the M direct digital frequency synthesizers so that the M direct digital frequency synthesizers output M modulation signals that cyclically switch N modulation frequencies and whose modulation frequencies are different from each other, and the optical comb generating apparatus supplies the M modulation signals as drive signals to the optical comb generating unit.

[0024] Furthermore, the present invention is an optical comb generating device, which is an optical comb distance measuring device for measuring distance based on the time difference between the interference signal of the measuring light and the interference signal of the reference light. It is characterized by comprising: N signal sources, wherein the N signal sources output N modulation signals with phases synchronized with the phase of the reference frequency signal and with different modulation frequencies as driving signals; an optical comb generating unit, which includes N optical comb generators, wherein the N optical comb generators are driven by the driving signals output from the N signal sources to generate N optical combs with periodically modulated intensity or phase and different modulation frequencies; an N-input M-output optical switch, which cyclically selects M optical combs with different modulation frequencies from the N optical combs generated by the N optical comb generators included in the optical comb generating unit and outputs the M optical combs; and an optical switch control unit, which controls the optical comb selection operation performed by the optical switch synchronously with the reference frequency signal.

[0025] Furthermore, in the optical comb generating apparatus according to the present invention, the drive control unit can be configured to perform the following control: the optical comb generating unit outputs M optical combs that cyclically switch N modulation frequencies in a switching sequence in one direction and the opposite direction, and the modulation frequencies are different from each other, wherein M is an integer of 2 or more, and N is an integer of 3 or more.

[0026] The effects of the invention

[0027] In this invention, by supplying M types of driving signals whose phases are synchronized with the phase of the reference frequency signal to the optical comb generation unit, the optical comb generation unit outputs M types of optical combs (M is an integer of 2 or more) whose intensity or phase is periodically modulated and whose N (N is an integer of 3 or more) modulation frequencies are cyclically switched and whose modulation frequencies are different from each other. As a result, in optical comb rangefinders and the like that which measure distance based on the time difference between the interference signal of the measurement light and the interference signal of the reference light, the phase shift caused by the signal transmission path other than the measurement object can be corrected, thereby obtaining the absolute distance result with high accuracy.

[0028] Furthermore, according to the present invention, an optical comb generating apparatus can be provided that can shorten the absolute distance measurement time and perform absolute distance measurement with high accuracy for moving bodies that require shorter absolute distance measurement time as their movement speed increases. Attached Figure Description

[0029] Figure 1 This is a block diagram illustrating a structural example of a comb generating apparatus to which the present invention is applied.

[0030] Figure 2 This is a state transition diagram showing the state transitions of the drive signals supplied to the two optical comb generators in the aforementioned optical comb generating apparatus.

[0031] Figure 3 This is a block diagram showing a specific structural example of the switching section in the aforementioned optical comb generating device.

[0032] Figure 4 This is a block diagram illustrating other structural examples of the optical comb generating apparatus to which the present invention is applied.

[0033] Figure 5 This is a block diagram illustrating a structural example of a frequency converter used in an optical comb generating apparatus.

[0034] Figure 6 This is a block diagram showing the basic structure of a comb generating device configured to drive a comb generator via a DDS oscillator.

[0035] Figure 7 This is a block diagram illustrating a structural example of an optical comb generating apparatus according to the present invention, which is configured to drive an optical comb generator via a DDS oscillator.

[0036] Figure 8 This is a block diagram illustrating a structural example of an optical comb generating device according to the present invention, which is configured to switch the optical comb via an optical switch. Detailed Implementation

[0037] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Furthermore, common indicator marks are used to illustrate common constituent elements in the drawings. It is self-evident that the present invention is not limited to the examples below, and various modifications can be made without departing from the spirit of the invention.

[0038] The present invention is applied to a light comb generating apparatus 10, which, for example... Figure 1 As shown in the block diagram, it has two optical comb generators 16A and 16B that emit interferometric measurement light and reference light, which are periodically modulated in intensity or phase and at different modulation frequencies.

[0039] The optical comb generating device 10 is used, for example, in optical comb rangefinders and three-dimensional shape measuring machines that measure distance based on the time difference between the interference signal of the measurement light and the interference signal of the reference light, as described in Patent Documents 1 and 2, to emit interferometric measurement light and reference light that are periodically modulated in intensity or phase and have different modulation frequencies.

[0040] The optical comb generating device 10, through an optical comb generating unit 16 which receives N (N is an integer of 3 or more) types of drive signals with cyclically switched modulation periods and different modulation frequencies from the drive control unit 11, outputs M (M is an integer of 2 or more) types of optical combs with periodically modulated intensity or phase and N (N is an integer of 3 or more) types of modulation frequencies cyclically switched and different modulation frequencies. Here, let N=4 and M=2. The drive control unit 11 provides the M (M=2) types of drive signals F with cyclically switched modulation frequencies and different modulation frequencies to the M (M=2) optical comb generators 16A and 16B provided by the optical comb generating unit 16. mA F mB Thus, the outputs from the aforementioned optical comb generators 16A and 16B are M (M=2) optical combs whose intensity or phase is periodically modulated and whose N (N=4) modulation frequencies are cyclically switched and whose modulation frequencies are different from each other.

[0041] The drive control unit 11 in the optical comb generating device 10 includes: a modulation signal generating unit 12, which generates a reference frequency signal F with phase and frequency provided by the reference oscillator 12R. REF N (N=4) types of modulation signals F that are phase-synchronized, have fixed frequencies, and have different frequencies. m1 F m2 F m3 F m4 N (N=4) PLL oscillators 12A, 12B, 12C, and 12D; a switching section 14 with N (N=4) inputs and M (M=2) outputs, from which N (N=4) types of modulation signals F are input from the modulation signal generation section 12 to the switching section 14. m1 F m2 F m3 F m4 ; and control unit 15, which modulates the signal F generated by the switching unit 14 m1 F m2 F m3 F m4 The output can be selected for switching control.

[0042] The first PLL oscillator 12A generates a reference frequency signal F whose phase is synchronized with that generated by the aforementioned reference oscillator 12R through the PLL circuit. REF The phase is synchronized and fixed at the first frequency f.m (f m The first modulation signal F (25000MHz) m1 .

[0043] In addition, the second PLL oscillator 12B generates a reference frequency signal F whose phase is synchronized with that generated by the aforementioned reference oscillator 12R through the PLL circuit. REF The phase is synchronized and fixed at the second frequency f. m +Δf m (f m +Δf m The second modulation signal F (25010MHz) m2 .

[0044] In addition, the third PLL oscillator 12C generates a reference frequency signal F whose phase is synchronized with that of the reference oscillator 12R by the PLL circuit. REF The phase is synchronized and fixed at the third frequency f. m +Δf(f m The third modulation signal F (+Δf=25000.5MHz) m3 .

[0045] Furthermore, the fourth PLL oscillator 12D generates a reference frequency signal F whose phase is synchronized with that generated by the aforementioned reference oscillator 12R via the PLL circuit. REF The phase is synchronized and fixed at the fourth frequency f. m +Δf+Δf m (f m +Δf+Δf m The fourth modulation signal F (25010.5MHz) m4 .

[0046] Furthermore, in this drive control unit 11, isolators 13A, 13B, 13C, and 13D are inserted between the modulation signal generation unit 12 and the switching unit 14, so that N (N=4) types of modulation signals F are input from the modulation signal generation unit 12 to the switching unit 14 via the isolators 13A, 13B, 13C, and 13D. m1 F m2 F m3 F m4 .

[0047] By inserting isolators 13A, 13B, 13C, and 13D as described above, a frequency signal F is input from the modulation signal generation unit 12 to the switching unit 14 via isolators 13A, 13B, 13C, and 13D. m1 F m2 F m3 F m4It can prevent the signal source (PLL oscillator 12A, 12B, 12C, 12D) from becoming unstable due to load changes caused by the cutting off or releasing of the circuit after the switch section 14.

[0048] The aforementioned isolators 13A, 13B, 13C, and 13D can use isolation elements such as microwave amplifiers with large reverse isolation, π-type resistor attenuators, T-type resistor attenuators, microwave isolators using ferrite, isolator circuits composed of variable attenuators and bandpass filters, and isolator circuits composed of isolation amplifiers, resistor attenuators, and bandpass filters.

[0049] Furthermore, the aforementioned switch unit 14 functions as a 4-input 2-output selection switch, receiving four modulation signals F from the aforementioned modulation signal generation unit 12 via the aforementioned isolators 13A, 13B, 13C, and 13D. m1 F m2 F m3 F m4 The signal is alternately output from two output terminals in a cyclic switching manner to switch cyclically as the drive signal F. mA F mB The four modulation signals F supplied to the two optical comb generators 16A and 16B of the optical comb generating unit 16 connected to the two output terminals are as follows: m1 F m2 F m3 F m4 .

[0050] like Figure 2 The diagram shows the drive signal F in the two optical comb generators 16A and 16B of the optical comb generating unit 16 in the optical comb generating apparatus 10. mA F mB In the manner of state transition, the aforementioned switch section 14 cyclically switches as the drive signal F. mA F mB The four modulation signals F supplied to the optical comb generators 16A and 16B are as follows: m1 F m2 F m3 F m4 .

[0051] Here, as the reference light pulse and the measurement light pulse used for absolute distance measurement requiring frequency switching in the optical comb rangefinder and three-dimensional shape measuring machine described in Patent Documents 1 and 2, the optical comb generating device 10 generates two optical combs to convert the above four modulation signals F m1 F m2 F m3 F m4 The aforementioned switch section 14 is used as the drive signal F in a cyclic switching manner. mAF mB The optical combs are supplied to the optical comb generators 16A and 16B, and as shown in Table 1, two optical combs with different modulation frequencies are output from the optical comb generators 16A and 16B, with their modulation frequencies being cyclically switched.

[0052] [Table 1]

[0053]

[0054] Table 1 shows the drive signals F of the two comb generators 16A and 16B in settings #1 to #4. mA F mB The transition states OFCG1 / OFCG2 and the phase difference, the frequency of the driving signal is, for example, Δf = 500kHz, Δf m =10MHz, f m =F m1 (25000MHz), f m +Δf m =F m2 (25010MHz), f m +Δf=F m3 (25000.5MHz), f m +Δf m +Δf=F m4 (25010.5MHz).

[0055] Figure 2 This indicates the drive signal F supplied to the two optical comb generators 16A and 16B in the optical comb generating device 10. mA F mB The state transition diagram.

[0056] In this optical comb rangefinder, in principle, two optical comb generators driven by two modulation signals of different frequencies pulse with interferometric characteristics, namely, reference light pulses and measurement light pulses, are emitted in a pulsed manner. The signal processing unit performs frequency analysis on the interference signal obtained by the reference photodetector (hereinafter referred to as the reference signal) and the interference signal obtained by the measurement photodetector (hereinafter referred to as the measurement signal). The mode number, starting from the center frequency of the optical comb, is designated as P. The phase difference between the P modes of the reference signal and the measurement signal is calculated to cancel the optical phase difference during the optical comb generation and transmission process from the optical comb generator to the reference point. Then, the phase difference of the signal pulse is determined by calculating the increment of the phase difference at each step on the frequency axis, thereby calculating the distance from the reference point to the measurement surface.

[0057] Furthermore, when the measurement distance exceeds the modulation frequency f mWhen the object light reaches half its wavelength, due to the periodicity of the object light, distances that are integer multiples of that half wavelength become ambiguous and cannot be uniquely determined. Therefore, four measurements are performed using a reference light pulse and a measurement light pulse set to the four modulation frequencies shown in Table 1. In the signal processing unit, the phase differences obtained by performing the same processing are used to calculate the ambiguous distance (La = c / 2f) that exceeds half the wavelength. m The distance (c: speed of light).

[0058] That is, regarding the phase difference between the reference signal and the measurement signal obtained by measuring the four modulation frequencies shown in Table 1, the modulation frequency of the modulation signal used to drive the two optical comb generators (OFCG1, OFCG2) is f. m and f m With the setting of +Δf #1, the above phase difference is -2πf m T, at the modulation frequency f of the modulating signal m +Δf m and f m +Δf m With the setting of +Δf #2, the above phase difference is -2π(f m +Δf m T, at the modulation frequency f of the modulating signal m +Δf and f m Under setting #3, the aforementioned phase difference is -2π(f) m +Δf)T, at the modulation frequency of the modulating signal f m +Δf m +Δf and f m +Δf m Under setting #4, the aforementioned phase difference is -2π(f) m +Δf m +Δf)T.

[0059] In comparing distances (La=c / 2f) m When c: speed of light) is long, the phase difference between the reference signal and the measured signal is (-2πf) m When m is set to an integer, T) takes the form φ+2mπ. Only the φ part can be calculated, and the integer value m is unknown.

[0060] On the other hand, the phase difference between the reference signal and the measured signal under setting #1 is -2πf m The phase difference between the reference signal and the measured signal under the same T#2 setting is -2π(f m +Δf m The difference between T and T is 2πΔf m T, Additionally, the phase difference between the reference signal and the measured signal under setting #3 is -2π(f m+Δf)T The phase difference between the reference signal and the measured signal under the same setting as #4 is -2π(f m +Δf m The difference between +Δf)T is 2πΔf m T, if it is related to Δf m The distance equivalent to half the wavelength (if Δf) m If the frequency is 10MHz, then La is within 15m, and the phase is uniquely determined.

[0061] Furthermore, by multiplying this phase by f m / Δf m By comparing the phase difference with #1, the integer m can be determined.

[0062] Furthermore, the phase difference -2πf is set according to #1 in Table 1. m The phase difference between T and #3 is -2π(f) m The difference between +Δf)T can yield 2πΔfT.

[0063] Furthermore, according to the setting of #2 in Table 1, the phase difference is -2π(f) m +Δf m The phase difference between T and #4 is -2π(f) m +Δf m The difference between +Δf)T can yield 2πΔfT.

[0064] Here, let f be the value. m =25GHz, Δf=500kHz, Δf m With a frequency of 10 MHz, since Δf = 500 kHz, distance measurements within a range of La = 300 m are possible.

[0065] In the optical comb rangefinder equipped with the optical comb generating device 10, absolute distance measurement is performed using a reference signal and a measurement signal obtained by measuring four modulation frequencies set as shown in Table 1. That is, after maintaining a state for a fixed time, the rangefinder transitions to another state, measures the signal phase of that state within a fixed interval, and uses the phase of the set states #1, #2, #3, and #4 to perform the calculation of the absolute distance.

[0066] Regarding the measurement speed in the optical comb rangefinder, it is equal to 500kHz for relative distance measurements within 6mm. In contrast, for absolute distance measurements that require frequency switching, the time for frequency switching and the time for absolute distance calculation are included.

[0067] In the optical comb generating device 10 described above, the four modulation signals F are... m1 F m2 F m3 F m4By cyclically switching the switch section 14 described above, the driving states of the two optical comb generators 16A and 16B are rapidly changed, thereby shortening the absolute distance measurement time by using the two optical comb light sources that are used as the modulation frequency for switching reference signals and measurement signals.

[0068] That is, as will be described later, if the oscillation frequency of a PLL oscillator that can be freely switched and set is used to switch and set the oscillation frequency in real time to obtain M modulation signals with different modulation frequencies, the adjustment time required to switch the oscillation frequency and use the set frequency to synchronize the phase to obtain a stable frequency signal at the target frequency is long. As a result, the absolute distance measurement is time-consuming and impractical for applications such as distance measurement of moving objects that require rapid measurement processing. However, in this optical comb generating device 10, the absolute distance measurement time can be shortened and the absolute distance measurement can be performed with high accuracy for moving objects whose moving speed is faster.

[0069] Furthermore, in this case, if it is only a distance measurement within 15m, it can be performed using only settings #1 and #2, or only settings #3 and #4. However, by setting #1, #2, #3, and #4 as described above, that is, by cyclically switching the four modulation frequencies F by the aforementioned switch unit 14, the above four modulation frequencies F can be achieved. m1 F m2 F m3 F m4 This technology extends the distance measurement range to over 300m and corrects for phase shifts caused by signal transmission paths other than the measured object, thus obtaining high-precision absolute distance results. Specifically, when the modulation frequencies of the two optical comb generators (OFCG1, OFCG2) 16A and 16B are changed, the absolute value of the phase caused by the distance to the measured object remains unchanged, but the sign is reversed. On the other hand, the sign of the shift caused by the cable length of the interference signal transmission path remains unchanged and is a fixed value. Therefore, by subtracting the results of the two phase measurements and dividing by 2, the phase value that has eliminated the shift can be obtained.

[0070] Regarding the state transitions in the loop, starting from #1, the switching is set up so that the sequence is #3, #2, #4, #2, #3, and then back to #1. This setting is determined considering the following: distance calculations are performed by taking into account both the measurement results obtained by changing the frequencies of OFCG1 and OFCG2 and the results obtained by reversing the frequency changing order. This ensures that distance calculations are performed with minimal distance measurement error and in the shortest time, even when the measured object is moving at speed.

[0071] In principle, the switching order of the four modulation frequencies shown in Table 1 is arbitrary when performing two phase measurements to obtain phase values ​​that exclude phase shift. However, by adopting a cyclical switching method that repeats #1→#2→#3→#4→#4→#3→#2→#1 and #1→#3→#2→#4→#4→#2→#3→#1, the distance measurement error and measurement processing time can be reduced.

[0072] Furthermore, when performing absolute distance measurements, the frequency "transition states" are generally grouped into four sets for distance calculation. However, in principle, the possibility of Δf cannot be ruled out. m =Δf, therefore it is also possible to use f m f m +Δf、f m The optical comb generating apparatus of the present invention utilizes three modulation frequencies: +2Δf. It comprises an optical comb generating unit that outputs M (M is an integer of 2 or more) optical combs whose modulation frequencies are periodically switched and are respectively modulated in intensity or phase, and which controls the output of the M optical combs by supplying M types of drive signals to the optical comb generating unit to synchronize the phase with the reference frequency signal. This allows for rapid switching of the drive states of the two optical comb generators, thereby shortening the absolute distance measurement time by using two optical comb light sources that are used to switch the modulation frequencies of the reference signal and the measurement signal.

[0073] Here, Figure 3 This is a block diagram showing a specific structural example of the 4-input, 2-output switch section 14 of the aforementioned optical comb generating device 10.

[0074] That is, regarding the switch section 14, as Figure 3 As shown in the block diagram, four modulation signals F generated by the PLL oscillators 12A, 12B, 12C, and 12D of the modulation signal generation unit 12 are input via isolators 13A, 13B, 13C, and 13D connected to the modulation signal generation unit 12. m1 F m2 F m3 F m4 The primary circuit consists of four switching circuits with one input and two outputs, 14 in total. 1A 14 1B 14 1C 14 1D via the aforementioned primary switching circuit 14 1A 14 1B 14 1C 14 1D The above four modulation signals F are inputm1 F m2 F m3 F m4 The next level is set with two switching circuits, each with 2 inputs and 1 output, 14. 2A 14 2B , and the two switching circuits 14 mentioned above 2A 14 2B Each output terminal is connected to the next level of two switching circuits with 1 input and 2 outputs. 3A 14 3B , and the two switching circuits 14 mentioned above 3A 14 3B The final stage of the connection consists of two switching circuits with 2 inputs and 1 output, respectively. 4A 14 4B The control unit (logic circuit) 15 communicates with the 10MHz reference frequency signal F. REF The switching control is performed synchronously, thus... Figure 2 The diagram shows the drive signal F in the two optical comb generators 16A and 16B mentioned above. mA F mB Like the state transition, it cyclically switches as the driving signal F. ma F mb The four modulation signals F supplied to the two optical comb generators 16A and 16B are as follows: m1 F m2 F m3 F m4 .

[0075] In this switching section 14, the primary four switching circuits 14 1A 14 1B 14 1C 14 1D One of their two output terminals is connected to the two switching circuits 14 in the next stage. 2A 14 2B One input terminal is connected, while the other output terminal is terminated by a terminating resistor.

[0076] In addition, Figure 3 In a specific example of the switching section 14 shown in the block diagram, four switching circuits 14 are connected to the primary side via isolators 13A, 13B, 13C, and 13D, which are composed of isolator circuits combining a variable attenuator (VAT) and a bandpass filter (BPC). 1A 14 1B 14 1C 14 1D Input the above four modulation signals F m1 F m2 F m3 Fm4 And from the two switching circuits 14 in the final stage 4A 14 4B The output terminals output the four cyclically switched modulation signals F via first and second bandpass filters 14A and 14B, which are respectively composed of isolator circuits combining isolation amplifiers and bandpass filters (BPC). m1 F m2 F m3 F m4 .

[0077] then, Figure 4 The optical comb generating device 20 shown above up-converts the 1GHz band frequency signals F1, F2, F3, and F4 generated by the modulation signal generating unit 12 through frequency converters 23A and 23B to obtain a 25GHz band modulation signal F. mA F mB to serve as a guide Figure 1 The drive signals supplied by the two optical comb generators 16A and 16B in the optical comb generating device 10 shown.

[0078] The drive control unit 11 of the optical comb generating device 20 has a modulation signal generating unit 12 that includes four PLL oscillators 12A, 12B, 12C, and 12D that generate frequency signals F1, F2, F3, and F4 in the 1GHz band, and a PLL oscillator 12E that generates a 24GHz frequency signal F0.

[0079] In this optical comb generating device 20, the fifth PLL oscillator 12E of the modulation signal generating unit 12 uses a PLL circuit to synchronize its phase with the reference frequency signal F supplied from the reference oscillator 12R. REF A 24GHz frequency signal F0 with phase synchronization and fixed frequency f0 is supplied to the two frequency converters 23A and 23B via power divider 21.

[0080] Furthermore, in the modulation signal generation unit 12 described above, the first PLL oscillator 12A generates a reference frequency signal F whose phase is made similar to, for example, 10MHz generated by the reference oscillator 12R through the PLL circuit. REF Phase synchronization and frequency fixed at f m '(f m The first frequency signal F1 is 1000MHz.

[0081] In addition, the second PLL oscillator 12B generates a reference frequency signal F whose phase is synchronized with that generated by the aforementioned reference oscillator 12R through the PLL circuit. REF Phase synchronization and frequency fixed at f m '+Δf m (f m'+Δf m The second frequency signal F2 (=1010MHz).

[0082] In addition, the third PLL oscillator 12C generates a reference frequency signal F whose phase is synchronized with that of the reference oscillator 12R by the PLL circuit. REF Phase synchronization and frequency fixed at f m '+Δf(f m The third frequency signal F3 is (+Δf=1000.5MHz).

[0083] Furthermore, the fourth oscillator 12D generates a reference frequency signal F whose phase is synchronized with that generated by the aforementioned reference oscillator 12R via a PLL circuit. REF Phase synchronization and frequency fixed at f m '+Δf m +Δf(f m '+Δf+Δf m The fourth frequency signal F4 (1010.5MHz)

[0084] In the modulation signal generation unit 12, the first to fourth frequency signals F1, F2, F3, and F4 obtained by the first to fourth PLL oscillators 12A, 12B, 12C, and 12D are input to the 4-input 2-output switching unit 14 via isolators 13A, 13B, 13C, and 13D.

[0085] The aforementioned switch unit 14 functions as a 4-input 2-output selection switch, and is connected to the reference frequency signal F provided by the reference oscillator 12R of the aforementioned modulation signal generation unit 12. REF Synchronously, the first to fourth frequency signals F1, F2, F3, and F4, which are input to the four input terminals from the modulation signal generation unit 12 via isolators 13A, 13B, 13C, and 13D, are cyclically output from the two output terminals to supply the two frequency converters 23A and 23B with first and second modulation signals F1 and F2, which cyclically switch the four frequency signals F1, F2, F3, and F4 of the 1GHz band. ma F mb .

[0086] Here, isolators 13A, 13B, 13C, and 13D are inserted between the modulation signal generation unit 12 and the switching unit 14. Frequency signals F1, F2, F3, and F4 are input from the modulation signal generation unit 12 to the switching circuit 14 via the isolators 13A, 13B, 13C, and 13D. This prevents the signal source from becoming unstable due to load fluctuations caused by the cutting off or releasing of circuits after the switching circuit 14.

[0087] The aforementioned isolators 13A, 13B, 13C, and 13D can use isolation elements such as microwave amplifiers with large reverse isolation, π-type resistor attenuators, T-type resistor attenuators, microwave isolators using ferrite, isolator circuits composed of variable attenuators and bandpass filters, and isolator circuits composed of isolation amplifiers, resistor attenuators, and bandpass filters.

[0088] Furthermore, the first and second frequency converters 23A and 23B use a frequency signal F0 (e.g., 24 GHz) supplied from the fifth PLL oscillator 12E, and four frequencies f that cyclically switch the 1 GHz band from the switching section. m =1000MHz, f m '+Δf m =1010MHz, f m +Δf=1000.5MHz, f m '+Δf m The first and second modulation signals F are alternately output from frequency signals F1, F2, F3, and F4 with a frequency of +Δf = 1010.5MHz. ma F mb To obtain four modulation frequencies f that can be converted into a 25GHz frequency band. m =25000MHz, f m +Δf m =25010MHz, f m +Δf=25000.5MHz、f m +Δf m The first and second modulation signals F, with a frequency of +Δf = 25010.5MHz, are... mA F mB And as a driving signal, it is supplied to the first and second optical comb generators 16A and 16B.

[0089] That is, the first and second frequency converters 23A and 23B mentioned above function as upconverters, converting the first and second modulation signals F1, F2, F3, and F4, which are composed of frequency signals F1, F2, F3, and F4 in the 1GHz band, into frequency converters. ma F mb The frequency is converted to become the first and second modulation signals F in the 25GHz band, which are supplied as driving signals to the first and second optical comb generators 16A and 16B. mA F mB .

[0090] The first and second frequency converters 23A and 23B mentioned above use mixers such as diodes, double-balanced mixers, and IQ mixers, or for example... Figure 5 The structure shown utilizes a phase-synchronized frequency converter 23.

[0091] Here, when the first and second frequency converters 23A and 23B mentioned above use mixers such as diodes, double-balanced mixers, and IQ mixers, since the mixer is a non-linear element, it will generate a frequency component other than the required frequency component (f) in the setting states of #1, #2, #3, and #4 mentioned above. m f m +Δf m f m +Δf、f m +Δf m Frequency components other than +Δf) are used, so bandpass filters 24A and 24B are inserted at the output sides of the first and second frequency converters 23A and 23B respectively to supply only the required frequency components as driving signals to the optical comb generators 16A and 16B.

[0092] For example, in the first frequency converter 23A that uses a mixer, for example, in the case of setting #1, not only is the required f generated... m The frequency components also produce unwanted frequency components f. m +Sf b (Except for S=0) stray particles. Here, S is an integer, f b The frequency of the modulation signal before frequency conversion is input to mixer 23A. This frequency component is mixed with the first modulation signal F supplied as a drive signal to the first optical comb generator 16A. mA Sometimes, stray light can occur during the optical combing process performed by the first optical comb generator 16A, affecting the measured values. To avoid this effect, a bandpass filter 24A is used to filter only the desired f-values. m The frequency components pass through, causing other frequency components to attenuate to a level that does not affect the measurement specifications.

[0093] Additionally, the unwanted frequency component f generated by the first frequency converter 23A using a mixer m +Sf b It also propagates towards the power divider 21 on the input side. Since the power divider 21 also has less than ideal characteristics, it reaches the second frequency converter 23B. This undesirable frequency component f that reaches the second frequency converter 23B... m +Sf b During frequency conversion, f will be mixed into the output of the second frequency converter 23B. m +Sf b +S'(f b The frequency components of +Δf). Here, (f b +Δf) is the frequency of the modulation signal input to the frequency converter 23B before frequency conversion.

[0094] Here, S' is an integer. Since frequency components other than S+S'=0 will be in f... m +f b or f m -f b In addition, it is possible to make the required f m The frequency +Δf passes through a bandpass filter 24A to attenuate frequency components other than S+S'=0. However, the frequency component where S+S'=0 is f. m +S'Δf is the f that is related to the required S'=1. m Frequency components that are very close to +Δf are difficult to remove using the bandpass filter 24A, but the reflection components of the frequency converters 23A and 23B can be attenuated by inserting isolators 22A and 22B on the input side, respectively.

[0095] For the aforementioned isolators 22A and 22B, isolation elements such as microwave amplifiers with high reverse isolation, PI-type resistor attenuators, T-type resistor attenuators, microwave isolators using ferrite, isolator circuits composed of variable attenuators and bandpass filters, and isolator circuits composed of isolation amplifiers, resistor attenuators, and bandpass filters can be used.

[0096] In the aforementioned optical comb generating device 20, an optimal structure is adopted to improve performance by combining the components in practical use.

[0097] Furthermore, in the aforementioned optical comb generating device 20, when f b f b Setting +Δf to around 100MHz can predict an improvement of over 40dB in relative phase noise, but at f m =25GHz and in f b At 100MHz, bandpass filters 25A and 25B require filters with extremely high Q values ​​(above 2500) to reduce f. m +f b or f m -f b The scattered.

[0098] Here, for the frequency converters 23A and 23B mentioned above, it is also possible to use, as Figure 5 The structure shown utilizes a phase-synchronized frequency converter 23 instead of a diode, a double-balanced mixer, an IQ mixer, or other mixers.

[0099] The frequency converter 23 includes a phase comparator 231, a voltage-controlled oscillator 232, and a mixer 233. The phase comparator 231 controls the oscillation phase of the voltage-controlled oscillator 232, and the frequency signal output from the voltage-controlled oscillator 232 is branched and input to the mixer 233.

[0100] In this frequency converter 23, the modulation frequency f of the 100MHz band b The modulation signal F b The 24.9 GHz frequency signal F0, input to phase comparator 231, is used as a frequency f m -f b The frequency signal is supplied from the fifth PLL oscillator 12E to the mixer 233. The mixer 233 then obtains the modulation frequency f of the 25GHz band output from the voltage-controlled oscillator 232. m The modulation signal F m The frequency signal of the difference frequency fb' between the frequency signal F0 and the frequency signal F0 is obtained by the phase comparator 231 and modulated with the frequency f of the 100MHz band. b The modulation signal F b The phase comparison output obtained by performing a phase comparison is used to control the oscillation phase of the voltage-controlled oscillator 232, thereby outputting a phase from the voltage-controlled oscillator 232 that modulates with the modulation frequency f of the 100MHz band. b The modulation signal F b The phase-synchronized and fixed-frequency modulation frequency f of the 25GHz band m The modulation signal F m .

[0101] That is, when the frequency converter 23 is used as the frequency converter 23A described above, it supplies the phase comparator 231 with a first modulation signal F1, F2, F3, F4 of the 100MHz band that is cyclically switched by the switching unit 14. ma Therefore, the above difference frequency f is performed. b The frequency signal of ' and the first modulation signal F mentioned above ma The phase comparison is fed back to the voltage-controlled oscillator 232 to control the oscillation phase of the voltage-controlled oscillator 232, thereby enabling the output of the first modulation signal F in the 100MHz frequency band from the voltage-controlled oscillator 232. ma The frequency f of the 25GHz band obtained by upconversion mA The modulation signal F mA .

[0102] Furthermore, when the frequency converter 23 is used as the frequency converter 23B described above, it supplies the phase comparator 231 with a second modulation signal F1, F2, F3, F4 of the 100MHz band, which is cyclically switched by the switching unit 14. mb Therefore, the above difference frequency f is performed. b The frequency signal and the second modulation signal F mentioned above mb The phase comparison is fed back to the voltage-controlled oscillator 232 to control the oscillation phase of the voltage-controlled oscillator 232, thereby enabling the output of the second modulation signal F with a frequency band of 100MHz from the voltage-controlled oscillator 232. mb The frequency f of the 25GHz band obtained by upconversion mB The modulation signal F mB .

[0103] Here, in this frequency converter 23, the phase comparator 231 uses a phase comparator such as a double-balanced mixer, which results in low noise because it performs phase comparisons between the same frequencies. Furthermore, since the modulation frequency f... b Frequency comparison is performed within a 100MHz frequency band, thus increasing the control bandwidth, for example, to 10MHz or higher. Therefore, the relative phase noise of the outputs of frequency converters 23A and 23B becomes the modulation frequency f of the 100MHz band. b f b +Δf m The relative phase noise of the signal. Furthermore, because the PLL has a large control bandwidth, the adjustment time required to obtain a stable frequency signal at the target frequency can be reduced.

[0104] Furthermore, due to the modulation frequency f compared to the 100MHz band b or f b The control band for phase synchronization of the +Δf signal is large enough that the output of the frequency converter 23 is sufficiently large, thus reducing the spurious f of the voltage-controlled oscillator 232. m +f b or stray f m -f b .

[0105] Therefore, by using the frequency converter 23 that utilizes phase synchronization as the frequency converters 23A and 23B respectively, it is possible to eliminate the need for the output-side bandpass filters 23A and 23B, or to reduce the specifications of the output-side bandpass filters 23A and 23B.

[0106] Here, the PLL oscillator can freely switch and set its oscillation frequency. Therefore, the drive control unit 11 can obtain M modulation signals with different modulation frequencies from the M PLL oscillators by cyclically switching and setting the oscillation frequencies of the M PLL oscillators, without the need for a switching unit, and supply these M modulation signals as drive signals to the M optical comb generators. However, when switching and setting the oscillation frequency of the PLL oscillator, the adjustment time required to obtain a stable frequency signal at the target frequency by switching the oscillation frequency and using the set frequency to synchronize the phase is long. Therefore, in applications requiring rapid measurement and processing, it is not practical to switch and set the oscillation frequency of the PLL oscillator in real time to obtain M modulation signals with different modulation frequencies.

[0107] Furthermore, while switching and setting the oscillation frequency of a PLL oscillator in real time is impractical, it is possible to switch and set the oscillation frequency in real time for use with a DDS oscillator.

[0108] DDS is short for Direct Digital Frequency Synthesizer, known as an oscillator that can produce an output of any frequency simply by setting frequency data (phase increment). Figure 6 The block diagram shows a basic structural example of an optical comb generating device 30 configured such that an optical comb generator 36A is driven by an optical comb generator 36A having a drive control unit 31 that includes a modulation signal generating unit 32 that uses a DDS oscillator 33 to drive the optical comb generating unit 36.

[0109] The drive control unit 31 in the optical comb generating device 30 consists of a modulation signal generating unit 32 that uses a DDS oscillator 33 and a DDS control unit 35 that controls the operation of the DDS oscillator 33. Modulation signals of various modulation frequencies are supplied from the DDS oscillator 33, which is controlled by the DDS control unit 35, to the optical comb generator 36A of the optical comb generating unit 36 ​​as drive signals.

[0110] The modulation signal generation unit 32 includes a reference frequency signal F generated by the reference signal generator 32R. REF The PLL oscillator 32A that synchronously generates the system clock and the DDS oscillator 33 that is driven according to the system clock are controlled by the DDS control unit 35 to switch frequencies in a phase-continuous state at any timing set by the DDS control unit 35, and the DDS oscillator 33 outputs modulation signals of various modulation frequencies.

[0111] The optical comb generator 36A of the optical comb generating unit 36 ​​is driven by a modulation signal supplied from the DDS oscillator 33 as a drive signal, which can be instantaneously switched to various modulation frequencies, thereby generating an optical comb.

[0112] Here, unlike oscillators based on phase synchronization, the DDS oscillator 33 is driven by the system clock, reads the waveform data from the ROM table within the selected DDS, performs DA conversion, and outputs a frequency signal. Therefore, it can switch frequencies instantaneously, without the buffer time required for phase synchronization. This simplifies the optical comb generation system for modulation frequency switching and reduces the wasted buffer time, thus facilitating high-speed measurement.

[0113] Figure 7 The optical comb generating device 40 shown in the block diagram is configured as an optical comb rangefinder that uses multiple, i.e., M (here, M=2) DDS oscillators 33A, 33B to drive the switching modulation frequencies of the reference signal and the measurement signal to perform absolute distance measurement. It also includes multiple, i.e., M (here, M=2) optical comb generators 36A, 36B.

[0114] In this optical comb generating device 40, DDS oscillators 33A and 33B are able to operate according to a reference frequency signal F generated by the reference signal generator 32R. REF Driven synchronously by the system clock generated by the PLL oscillator 32A, the frequency is switched in a phase-continuous state at arbitrary timings set by the DDS control unit 35 to output modulation signals of various modulation frequencies. Here, four frequencies f in the 1GHz band are used. m =1000MHz, f m '+Δf m =1010MHz, f m +Δf=1000.5MHz, f m '+Δf m +Δf=1010.5MHz became Figure 2 The timing of the transition state shown is cyclically switched by the first and second modulation signals F. ma F mb Output alternately.

[0115] Furthermore, the drive control unit 31 in the optical comb generating device 40 controls the four frequencies f of the 1GHz band generated by the DDS oscillators 33A and 33B of the modulation signal generating unit 12. m =1000MHz, f m '+Δf m =1010MHz, f m +Δf=1000.5MHz, f m '+Δf m +Δf=1010.5MHz is the first and second modulation signals F that are cyclically switched. ma F mbThe modulation signal F in the 25GHz band is obtained by up-conversion using frequency converters 42A and 42B. mA F mB and modulate the signal F mA F mB The drive signal is supplied to the two optical comb generators 16A and 16B of the optical comb generator 36.

[0116] That is, the modulation signal generation unit 32 in the optical comb generation device 40 has a reference frequency signal F generated by the reference signal generator 32R. REF A PLL oscillator 32B synchronously generates a frequency signal with a frequency of 24 GHz. The frequency signal generated by the PLL oscillator 33B with a frequency of 24 GHz is supplied to the frequency converters 42A and 42B via isolators 41A and 41B, thereby converting the first and second modulation signals F of the 1 GHz band generated by the DDS oscillators 33A and 33B into a frequency signal. ma F mb The modulation signal F, which is up-converted to a 25GHz frequency band by the aforementioned frequency converters 42A and 42B, is... mA F mB and modulate the signal F mA F mB As driving signals, they are supplied to the two optical comb generators 36A and 36B of the optical comb generator 36 via bandpass filters 43A and 43B.

[0117] In addition, by Figure 5 The frequency converter 23 shown, which utilizes phase synchronization, is used as the aforementioned frequency converters 42A and 42B. It can eliminate the need for the output-side bandpass filters 43A and 43B, or reduce the specifications of the output-side bandpass filters 43A and 43B.

[0118] In this optical comb generating device 40, by controlling the operation of the DDS oscillators 33A and 33B by the DDS control unit 35, the modulation frequency can be cyclically switched in a phase-continuous state to quickly change the driving state of the two optical comb generators 36A and 36B provided by the optical comb generator 36. By using the modulation frequency used to switch the reference signal and the measurement signal to perform absolute distance measurement, the measurement time of absolute distance can be shortened.

[0119] Here, in the aforementioned optical comb generating devices 10, 20, and 40, N = 4 and M = 2 are set, and N (N = 4) types of modulation frequencies are cyclically switched and the modulation frequencies are different from each other from the two optical comb generators 16A and 16B (36A and 36B) of the optical comb generating unit 16 (36). However, the number of modulation frequencies N is not limited to N = 4, as long as it is an integer of 3 or more. In addition, the number of optical comb generators M is not limited to M = 2, as long as it is an integer of 2 or more. The drive control unit 11 (31) performs the following drive control: supplying phase and reference frequency signals F to the optical comb generating unit 16 (36). REF The phase is synchronized and the N types of modulation frequencies are cyclically switched and the M types of driving signals with different modulation frequencies are used to make the optical comb generation unit 16 (36) output M types of optical combs.

[0120] For example, in the aforementioned optical comb generating apparatuses 10 and 20, the drive control unit 11 can be configured to output a reference frequency signal F whose phase is compared with that provided by the reference frequency signal generator 12R. REF The N modulation signals with different phases and different oscillation frequencies are cyclically switched to obtain M modulation signals with different modulation frequencies. For example, the N modulation signals with different oscillation frequencies obtained from the N PLL oscillators are cyclically switched by the N-input M-output switching unit 14 to obtain M modulation signals with different modulation frequencies. The above M modulation signals are supplied as driving signals to the M optical comb generators provided in the optical comb generation unit.

[0121] Furthermore, in the aforementioned optical comb generating device 40, the drive control unit 31 obtains a phase-to-reference frequency signal F by using M DDS oscillators. REF The N phase-synchronized modulation signals with different oscillation frequencies are cyclically switched with M modulation signals with different modulation frequencies. The above M modulation signals are used as driving signals to supply the M optical comb generators in the optical comb generation unit.

[0122] Furthermore, in the aforementioned optical comb generating devices 10 and 20, the drive control unit 11 is configured as a switch unit 14 that outputs M through N input, which modifies the phase with the reference frequency signal F provided by the reference frequency signal generator 12R. REF The phase-synchronized N modulation signals with different oscillation frequencies are cyclically switched, and M modulation signals with different modulation frequencies are used as driving signals to make the M optical comb generators in the optical comb generation unit output M optical combs, but it can also be like Figure 8 As shown in the optical comb generating device 50, it is also possible to cyclically select and output M optical combs with different modulation frequencies from the N optical combs generated by the N optical comb generators 16A, 16B, ... that generate N optical combs with different modulation frequencies through the N-input M-output optical switch 31.

[0123] In this case, it is not necessary for all optical combs to have different modulation frequencies; even if some have the same modulation frequency but different wavelengths, they can still be used for other switching. To achieve interference, a set of optical combs with different modulation frequencies in the same wavelength band must be included, but even combinations of the same modulation frequencies including optical combs with other wavelength bands will function.

[0124] Here, assuming N=4 and M=2, the optical comb generating unit 16 in the optical comb generating device 50 has four optical comb generators 16A, 16B, 16C, and 16D that generate four different optical combs with different modulation frequencies. The drive control unit 11 includes a modulation signal generating unit 12, which generates a reference frequency signal F whose phase is the same as that generated by the reference oscillator 12R. REF The system includes four PLL oscillators 12A, 12B, 12C, and 12D for N (N=4) phase-synchronized modulation signals; a 4-input, 2-output optical switch 51 that cyclically selects two optical combs with different modulation frequencies from the four optical combs generated by the optical comb generation unit 16 and outputs the two optical combs; and a control unit 52 that controls the optical comb selection operation performed by the 4-input, 2-output optical switch 51, driving the control unit 11 to cyclically select four optical combs with different modulation frequencies and wavelength bands through the 4-input, 2-output optical switch 51 to output the two optical combs.

[0125] The drive control unit 11 in the optical comb generating device 50 switches the optical comb, so there is no need to switch the modulation signals with different modulation periods generated by the modulation signal generating unit 12.

[0126] Explanation of reference numerals in the attached figures

[0127] 10, 20, 30, 40, 50: Optical comb generating unit; 11, 31: Drive control unit; 12, 32: Modulation signal generating unit; 12A, 12B, 12C, 12D, 12E, 32A, 32B: PLL oscillators; 12R, 32R: Reference signal oscillators; 13A, 13B, 13C, 13D, 22A, 22B, 41A, 41B: Isolators; 14: Switching unit; 14A, 14B, 24A, 24B 15, 43A, 43B: Bandpass filters; 16, 52: Control unit; 16, 36: Optical comb generation unit; 16A, 16B, 16C, 16D, 36A, 36B: Optical comb generators; 23, 23A, 23B: Frequency converters; 21: Power divider; 33, 33A, 33B: DDS oscillators; 35: DDS control unit; 51: Optical switch; 231: Phase comparator; 22: Voltage-controlled oscillator; 233: Mixer.

Claims

1. An optical comb generating device, which is an optical comb distance measuring device for measuring distance based on the time difference between the interference signal of a measured light and the interference signal of a reference light, characterized in that, have: The optical comb generating unit has M optical comb generators, among which... M is an integer greater than 2; and The drive control unit performs the following control: it supplies M types of drive signals, each with a phase synchronized with the phase of a reference frequency signal and with N different modulation frequencies, to the M optical comb generators, so that the optical comb generators output M types of optical combs. The optical comb generating unit outputs M optical combs from the M optical comb generators, each with its intensity or phase periodically modulated and N modulation frequencies cyclically switched, and the modulation frequencies being different from each other. The drive control unit also performs the following control: causing the optical comb generating unit to output M types of optical combs, the modulation frequency of the M types of optical combs cyclically switching between N types of modulation frequencies, the cyclic mode being configured to continuously operate along one direction and the opposite direction, and the modulation frequencies of the M types of optical combs being different from each other, wherein M is an integer greater than 2 and N is an integer greater than 3.

2. The optical comb generating apparatus according to claim 1, characterized in that, The drive control unit includes: N signal sources, wherein the N signal sources output N modulation signals whose phases are synchronized with the phase of the reference frequency signal and whose modulation frequencies are different from each other; The switch section with N inputs and M outputs is connected to the N signal sources; as well as The switching control unit controls the operation of the switching unit to output M modulation signals that cyclically switch between N modulation signals with different modulation frequencies. The optical comb generating device supplies the M types of modulation signals as driving signals to the M optical comb generators.

3. The optical comb generating apparatus according to claim 2, characterized in that, The N signal sources generate N modulation signals, each with a phase-locked loop circuit that synchronizes its phase with the phase of the reference frequency signal and has a fixed modulation frequency.

4. The optical comb generating apparatus according to claim 1, characterized in that, The drive control unit includes: A signal source, comprising M direct digital frequency synthesizers, which operate according to a system clock whose phase is synchronized with the phase of the reference frequency signal; and A switching control unit controls the operation of the M direct digital frequency synthesizers, causing the M direct digital frequency synthesizers to output M modulation signals that cyclically switch between N modulation frequencies, each with a different modulation frequency. The optical comb generating device supplies the M types of modulation signals as driving signals to the optical comb generating unit.

5. An optical comb generating device, which is an optical comb distance measuring device for measuring distance based on the time difference between the interference signal of a measured light and the interference signal of a reference light, characterized in that, have: N signal sources, wherein the N signal sources output N kinds of modulation signals whose phases are synchronized with the phase of the reference frequency signal and whose modulation frequencies are different, as driving signals; The optical comb generating unit has N optical comb generators, which are driven by driving signals output from the N signal sources to generate N optical combs whose intensity or phase is periodically modulated and whose modulation frequencies are different from each other. An N-input, M-output optical switch cyclically selects M optical combs with different modulation frequencies from the N optical combs generated by the N optical comb generators in the optical comb generation unit and outputs the M optical combs; and An optical switch control unit synchronously controls the selection action of the optical comb performed by the optical switch in accordance with the reference frequency signal; The optical switch control unit synchronously controls the optical comb selection operation performed by the optical switch with the reference frequency signal, so that the optical comb generation unit outputs M optical combs. The modulation frequency of the M optical combs cycles between N modulation frequencies. The cycle mode is configured to continuously switch along one direction and the opposite direction, and the modulation frequencies of the M optical combs are different from each other. Here, M is an integer greater than 2 and N is an integer greater than 3.

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