JP2023019066A - Optical comb distance measurement method and optical comb distance measurement device - Google Patents

Abstract

To provide an optical comb distance measurement method and an optical comb distance measurement device for measuring a distance from a time difference in interference signal of reference light and measurement light having passed through a measurement section, in which switching of frequency settings is carried out at high speed and a distance calculation is reliably conducted in a short time.SOLUTION: The present invention switches, by a state switching control unit 12, the state of modulation cycle of one or more sets of measurement light and reference light mutually differing in modulation cycle that are outputted from an optical comb light source 10, as well as causes the measurement light and reference light having been inputted from the optical comb light source 10 to be interfered in an interference unit 20 to generate interference light for reference and outputs one of the measurement light and the reference light toward a measurement object 50. Furthermore, the present invention causes the measurement light having reciprocated the distance to the measurement object 50 and the reference light to be interfered to generate interference light for measurement, detects the interference light for reference and the interference light for measurement by a reference light detector 23 and a measurement light detector 24, and calculates, by a signal processing unit 30, the distance to the measurement object 50 on the basis of a reference signal, a measurement signal, and the state signal outputted from the state switching control unit 12.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical comb distance measuring method and an optical comb distance measuring apparatus for measuring a distance from the time difference between the interference signals of the reference light and the measurement light, one of which passed through the measurement section.

2. Description of the Related Art Conventionally, distance measurement based on optical principles using laser light has been known as an active distance measurement method capable of precise point distance measurement. A laser rangefinder, which measures the distance to an object using a laser beam, detects the distance to the object based on the difference between the time when the laser beam is emitted and the time when the light receiving element detects the laser beam that hits and is reflected from the object to be measured. is calculated (see Patent Document 1, for example). In addition, for example, the driving current of the semiconductor laser is modulated with a triangular wave or the like, and the reflected light from the object is received using a photodiode embedded in the semiconductor laser element, and the sawtooth that appears in the photodiode output current is obtained. Distance information is obtained from the dominant wave number of the square wave.

A laser rangefinder is known as a device for measuring the absolute distance from a certain point to a measurement point with high accuracy. For example, Patent Literature 1 describes a rangefinder that measures a distance from a time difference between an interference signal of measurement light and an interference signal of reference light.

With conventional absolute distance meters, it is difficult to achieve a practical absolute distance meter that can measure long distances with high accuracy. I had no choice but to use an unsuitable method.

The inventors of the present invention are equipped with two optical comb generators that emit pulses of coherent reference light and measurement light whose intensity or phase is modulated periodically and whose modulation periods are different from each other. Interference light between the reference light pulse and the measurement light pulse irradiated on the measurement surface is detected by a reference light detector, and the reference light pulse reflected by the reference surface and the measurement light pulse reflected by the measurement surface are detected. The interference light is detected by the measurement photodetector, and the difference between the distance to the reference plane and the distance to the measurement plane is obtained from the time difference between the two interference signals obtained by the reference photodetector and the measurement photodetector. Therefore, an optical comb rangefinder that can be performed with high precision and in a short time has been proposed (see, for example, Patent Document 2).

In addition, we previously proposed an optical frequency comb rangefinder in which the position of the reference point for the distance to the measurement surface is defined by the reference optical path, enabling long-distance measurement with high accuracy and in a short period of time ( For example, see Patent Document 3).

In the optical comb rangefinder, signal processing is performed by using coherent reference light pulses and measurement light pulses emitted from two optical comb generators driven by two types of modulation signals with different frequencies in principle. In the section, frequency analysis is performed 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), and the optical comb The mode number counted from the center frequency is P, and the phase difference between the P-order modes of the reference signal and the measurement signal is calculated to cancel the optical phase difference in the optical comb generation and transmission process from the optical comb generator to the reference point. After that, the distance from the reference point to the measurement surface is calculated by calculating the increment of the phase difference per order on the frequency axis and obtaining the phase difference between the measurement signal pulse and the reference signal pulse.

Here, the reference light pulses output from two optical comb generators driven by a pair of modulation signals with a microwave band modulation frequency f _m (eg, 25 GHz) and a frequency difference Δf (eg, 500 kHz) and the measurement The distance measured using light pulses is the remainder of the total distance from the reference point to the measurement surface (referred to as the absolute distance) minus the integral multiple of half the wavelength of the modulation frequency _fm . The interference signal has a periodicity of Δf, and the phase difference between the closest reference signal and the measurement signal is obtained. When measuring a distance exceeding half a wavelength, a phase obtained by multiplying 2π by an integer exists as a phase corresponding to the time difference from the reference time to the reference signal being compared. One set of frequency settings cannot determine the integer value. By performing multiple distance measurements with slightly different modulation frequencies f _m , the integer can be calculated back as a value that meets multiple measurement conditions.

That is, in absolute distance measurement that requires frequency switching, the time required for measurement includes frequency switching time, measurement time, and absolute distance calculation time.

The frequencies of the modulation signals for driving the two optical comb generators can be switched by using a modulation signal generator whose frequency can be set by, for example, PLL (Phase-Locked Loop).

It is desirable that the signal for driving the optical comb generator has as little phase noise as possible. When synchronizing a VCO with low phase noise to an external reference signal, do not widen the control frequency band unnecessarily, and aim to clean up the drive signal so that the phase noise of the VCO is lower than that of the reference signal. As for the frequency band, the control band is limited so that the characteristics of the VCO can be obtained as they are.

The time it takes for the PLL frequency to settle down (settling time) can be thought of as roughly proportional to the reciprocal of the control band. Widening causes an increase in phase noise in the high frequency range and an increase in the mixed level of spurious signals related to the comparison frequency.

A reference on PLLs (Non-Patent Document 1) presents a design example of locking the frequency within an error of 1 kHz in about 51 microseconds, given a low-pass filter bandwidth of about 207 kHz. there is When setting the frequency divider so that 500 kHz is the unit of frequency setting, the bandwidth of the low-pass filter must be further lowered to avoid the inclusion of spurious, and the settling time is several times 51 microseconds. It is expected to take a long time.

Therefore, the two optical comb generators in the optical comb rangefinder are supplied as driving signals by switching a plurality of modulated signals whose frequency is fixed and phase-locked to the reference frequency signal by the PLL circuit. I was like

JP-A-2001-343234 Japanese Patent No. 5231883 JP 2020-12641 A

Analog Dialogue, AD33-03 Fundamentals of Phase-Locked Loops (PLLs) Author Ian Collins

As described above, in the conventional optical comb rangefinder, in principle, two optical comb generators driven by two types of modulated signals with different frequencies generate coherent reference light pulses and measurement light pulses. When the optical comb frequency interval between the reference light and the measurement light changes due to the switching of the frequencies of the reference light and the measurement light, the time at which the interference signal is generated and the time difference between the reference signal and the measurement signal change. If it is okay to apply the frequency, send a frequency switching command to the light source from an external central processing unit, etc., wait enough time until it is considered that the switching is completed, and after executing data collection and phase calculation, the next frequency from the central processing unit A plurality of relationships between frequency settings and phase values can be obtained by repeating the procedure of sending a frequency switching command to the settings and performing data collection and phase calculation after a sufficient period of time.

However, in the process of obtaining a set of phase values necessary for executing distance calculation, if the refractive index fluctuation of the air and slight vibration of the distance to be measured are mixed into the phase values as errors, it will be difficult to determine the order and calculate the distance. A set of data must be collected faster than changes in the air refractive index and changes in the measurement distance, as they cause errors.

In addition, in order to perform distance calculation reliably in a short time, it is necessary to check that the frequency setting is performed reliably, and to determine the reliability of the phase value, such as the frequency setting state corresponding to the phase value. is aligned with each phase value.

In order to switch the frequency setting state at high speed and calculate the distance in a short time, it is necessary to know which position in the waveform of the interference signal collected in the state of high speed switching is in which frequency state for each waveform. is required.

An object of the present invention is to provide an optical comb distance measurement method for measuring a distance from the time difference between an interference signal between a reference light and a measurement light and an interference signal between the reference light and the measurement light that has passed through a measurement section, in view of the conventional circumstances as described above. An optical frequency comb distance measuring device capable of quickly switching a frequency setting state and surely performing distance calculation in a short time.

Other objects of the present invention and specific advantages obtained by the present invention will become clearer from the description of the embodiments described below.

In the present invention, in measuring the distance from the time difference between the interference signals of the reference light and the measurement light, whichever one of the interference signals of the reference light and the measurement light passed through the measurement section, the interference signal of the optical comb rangefinder and the light source state signal are synchronously captured, the position of the waveform and the frequency setting of the optical comb at that position are clarified, and the distance is calculated. Get it right at the same time.

Using a state signal that indicates the frequency state of the measurement light and the reference light in the optical comb light source unit that outputs the measurement light and the reference light, the measurement data is captured in synchronization with the interference signal, and the section (location) of the waveform and its location By recording the waveform data by clarifying the frequency setting state, it is possible to confirm that the frequency state is constant in the waveform section to be processed and that it is an effective section as waveform data. and the frequency setting value for that section is used to convert the calculated phase value to delay time or distance.

That is, the present invention is an optical comb distance measurement method for measuring a distance from the time difference between the interference signals of the reference light and the measurement light in which one of the interference signals of the reference light and the measurement light has passed through the measurement section. a state switching step of switching the state of the modulation period of one or more sets of measurement light and reference light whose modulation periods are mutually different and whose intensity or phase is modulated dynamically, and outputting a state signal indicating the switching state; In the step, the measurement light whose modulation period state is switched and the reference light are caused to interfere with each other to generate reference interference light, and either the measurement light whose modulation period state is switched or the reference light is used as the measurement target. an interference step of generating interference light for measurement by interfering the measurement light and the reference light, which are output toward an object and one of which has reciprocated the distance to the measurement object, and the reference generated in the interference step; an interference light detection step of detecting the interference light for measurement and the interference light for measurement to obtain a reference signal and a measurement signal; the reference signal and the measurement signal obtained in the interference light detection step; and the state signal output in the state switching step. and a signal processing step of calculating the distance to the object to be measured based on.

In the optical comb distance measurement method according to the present invention, in the state switching step, X (integer of 3 or more) in which the N kinds of modulated signals, an integer of 3 or more, with mutually different frequencies are input via at least three isolators. Switching for selectively outputting the N kinds of modulated signals to the M (M is a positive integer) optical comb generators of the optical comb light source unit through the input Y (Y is a positive integer) output switch unit. A state indicating the switching state of the modulation period of the measurement light and the reference light emitted from the M optical comb generators in accordance with the selection state of the N types of modulation signals selected by the switch section. It can output a signal.

Further, in the optical frequency comb distance measuring method according to the present invention, in the state switching step, the modulation signal is input to at least two frequency converters to which a frequency signal obtained by one oscillator of the modulation signal generation unit provided with three oscillators is input. Each frequency signal obtained by each oscillator other than the one oscillator of the generating unit is switched by the switching unit to be input, and at least two types of modulated signals having different frequencies that are frequency-converted by the at least two frequency converters, is supplied as a drive signal to at least two optical comb generators of the optical comb light source unit, and from the at least two optical comb generators in accordance with the switching state of each frequency signal switched input to the two frequency converters. A state signal indicating a switching state of the modulation periods of the emitted measurement light and reference light may be output.

Further, in the optical comb distance measurement method according to the present invention, in the state switching step, from the N types of optical combs generated by the N optical comb generators of the optical comb light source unit, a switch unit using an optical switch , to perform selection control for cyclically selecting and outputting M types of optical combs with mutually different modulation periods, and to output a state signal indicating the selection state.

The present invention is an optical comb distance measuring device that measures a distance from the time difference between the interference signal of the reference light and the measurement light in which one of the interference signals of the reference light and the measurement light passes through the measurement section, and periodically an optical comb light source unit that outputs one or more sets of measurement light and reference light whose intensity or phase is modulated and whose modulation periods are different from each other; , a state switching control unit for outputting a state signal indicating the switching state; and a measurement light and a reference light are input from the optical comb light source unit, and interference between the input measurement light and the reference light is generated to generate a reference interference light. At the same time, one of the input measurement light and reference light is output toward the object to be measured, and one of them interferes with the measurement light and the reference light that have reciprocated the distance to the object to be measured. an interference section that generates interference light for measurement; a reference photodetector that detects the interference light for reference generated by the interference section and outputs a reference signal; and an interference light for measurement that is generated by the interference section. A measuring photodetector for detecting and outputting a measurement signal, a reference signal output from the reference photodetector, a measurement signal output from the measuring photodetector, and a state switching control section outputting and a signal processing unit that calculates the distance to the object to be measured based on the state signal.

In the optical comb distance measuring apparatus according to the present invention, the optical comb light source unit includes M (M is a positive integer) optical comb generators, and is selectively input via the state switching control unit. M types of optical combs whose modulation periods are different from each other and whose intensity or phase is periodically modulated by at least three types of modulation signals out of N types of modulation signals of three or more integers with different frequencies are provided. State-switched measurement light and reference light are output, and the state-switching control unit receives X(3 Integer) input Y (Y is a positive integer) output switch section, and selectively output the N types of modulated signals to the M optical comb generators of the optical comb light source section through the switch section. and switching states of the modulation periods of the measurement light beam and the reference light beam emitted from the M optical comb generators according to the selection state of the N types of modulation signals selected by the switch section. It may output a status signal indicating

Further, the optical comb distance measuring device according to the present invention includes a modulation signal generation section having at least three oscillators that generate frequency signals having different frequencies, and one oscillator among the three oscillators of the modulation signal generation section. and at least two frequency converters to which the frequency signals obtained by the oscillators other than the one oscillator are input, wherein the state switching control unit receives the frequency signals obtained by the oscillators other than the one oscillator. The obtained frequency signals are switched by the switch unit to be input to the at least two frequency converters, and at least two types of modulated signals having different frequencies frequency-converted by the at least two frequency converters are supplied to the optical comb. It is supplied as a drive signal to at least two optical comb generators of the light source unit and is emitted from the at least two optical comb generators in accordance with the switching state of each frequency signal switched input to the two frequency converters. A state signal indicating the switching state of the modulation periods of the measurement light and the reference light can be output.

Further, in the optical comb distance measuring apparatus according to the present invention, the optical comb light source unit is cyclically modulated in intensity or phase, and generates N types of optical combs of N types, which are an integer of 3 or more and have mutually different modulation periods. The state switching control unit selects M (M is a positive integer) types of optical combs are cyclically selected and output; and a control unit for controlling selection operation of the optical combs by the optical switch unit. Selection control is performed to cyclically select and output M types of optical combs with different modulation cycles from N types of optical combs through a switch unit using switches, and a state signal indicating the selection state is output. shall be allowed.

In the present invention, a state signal indicating the frequency state of the measurement light and the reference light in the optical comb light source unit that outputs the measurement light and the reference light is used to capture the measurement data in synchronization with the interference signal, and the waveform section (location ) and record the waveform data by clarifying the frequency setting state at that location, it is possible to confirm that the frequency state is constant without any change in the waveform section to be processed, and in the section that is valid as waveform data It is possible to determine that there is one, and the frequency setting value for that section can be converted from the calculated phase value to the delay time or distance.

That is, in the present invention, the interference signal of the optical frequency comb rangefinder and the light source state signal are synchronously captured, and the position of the waveform and the frequency setting of the optical frequency comb at that position are clarified to calculate the distance, thereby obtaining by signal processing. The phase value to be output and the frequency setting of the signal section in which the phase value is output can be obtained simultaneously and correctly, and the distance calculation can be reliably performed in a short time.

Therefore, according to the present invention, it is possible to provide an optical comb distance measurement method and an optical comb distance measurement device that can reliably perform distance calculation in a short time.

It is a block diagram which shows the structural example of the optical comb distance measuring device to which this invention is applied. It is a block diagram which shows the structural example of the optical comb light source part in the optical comb distance measuring device to which this invention is applied. FIG. 4 is a state transition diagram showing state transitions of drive signals supplied to two optical comb generators in the optical comb light source section; 3 is a block diagram showing a specific configuration example of a switch section of a state switching control section built in the optical comb light source section; FIG. It is process drawing which shows the procedure of the optical comb distance measuring method which concerns on this invention implemented by the said optical comb distance measuring device. It is process drawing which shows the concrete processing procedure of the signal processing process in the said optical comb distance measuring method. It is a block diagram which shows the other structural example of the optical comb light source part in the said optical comb distance measuring device. It is a block diagram which shows the other structural example of the optical comb light source part in the said optical comb distance measuring device. It is a block diagram which shows the structural example of the frequency converter of the said optical comb light source part. FIG. 11 is a block diagram showing still another configuration example of the optical comb light source unit in the optical comb distance measuring device to which the present invention is applied; FIG. 11 is a block diagram showing still another configuration example of the optical comb distance measuring device to which the present invention is applied; FIG. 11 is a block diagram showing still another configuration example of the optical comb distance measuring device to which the present invention is applied;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that common constituent elements will be described by attaching common reference numerals in the drawings. Further, the present invention is not limited to the following examples, and can be arbitrarily modified without departing from the gist of the present invention.

The present invention is applied to, for example, an optical comb distance measuring device 100 configured as shown in the block diagram of FIG.

This optical comb distance measurement device 100 measures the distance from the time difference between the interference signal between the reference light and the measurement light and the interference signal between the reference light and the measurement light that has passed through the measurement section. are modulated, and an optical comb light source unit 10 that outputs a set of measurement light and reference light with mutually different modulation periods, an interference unit 20 that receives the measurement light and the reference light from the optical comb light source unit 10, and the interference A signal processing unit 30 to which the reference signal and the measurement signal obtained by the unit 20 are input is provided.

The optical comb light source unit 10 includes a first optical comb generator 11A for emitting measurement light and a second optical comb generator 11B for emitting reference light. It incorporates a state switching control unit 12 that sets or reads the switching state of each modulation cycle state of the measurement light and the reference light emitted from 11A and 11B, and outputs a state signal indicating the switching state.

The optical comb light source unit 10 outputs one or more pairs of measurement light and reference light that are modulated periodically and have different modulation periods. can be used to set the switch or read the switch state. Also, the state switching control section 12 may be provided in a signal processing section like an optical comb distance measuring device 100B described later.

The interference unit 20 outputs either the measurement light or the reference light input from the optical comb light source unit 10 toward the measurement object 50, and the measurement light and the reference light do not travel the distance to the measurement object 50. The reference interference light is detected by the reference photodetector 23 and output as a reference signal. The interference light for measurement is detected by the photodetector 24 for measurement and output as a measurement signal. ) or a polarizing beam splitter (PBS) can be used.

In the interference unit 20 in the optical comb distance measuring device 100 shown in the block diagram of FIG. The measurement light is incident on the light mixing element 22A made up of a semitransparent mirror (BS) and is incident on the light mixing element 22A via the total reflection mirror 21, and is split into two mixed lights by the light mixing element 22A. One of the mixed lights is incident on the light separating/mixing element 22B composed of a polarizing beam splitter (PBS), and the other mixed light is incident on the reference photodetector 23, and the one mixed light enters the light separating/mixing element. 22B separates the reference light and the measurement light according to the polarization, the reference light is incident on the reference plane 25 via the quarter-wave plate 26A, and the measurement light is passed through the quarter-wave plate 26B. is incident on the object 50 to be measured. The reference light reflected by the light separating/mixing element 22B is incident on the reference plane 25 via the quarter-wave plate 26A, reflected by the reference plane 25, and passed through the quarter-wave plate 26A again. The reference light incident on the light separating/mixing element 22B has a plane of polarization orthogonal to the light separating/mixing element 22B. Then, the measurement light transmitted through the light separation/mixing element 22B enters the measurement object 50 via the quarter-wave plate 26B, is reflected by the measurement object 50, and passes through the quarter-wave plate 26B. The measurement light that passes through the light separation/mixing element 22B again and is incident on the light separation/mixing element 22B has a plane of polarization orthogonal to the measurement light, and the light separation/mixing element 22B passes through the quarter-wave plate 26B again. Reflect light. The quarter-wave plates 26A and 26B may each be a Faraday rotator.

Here, the reference light and the measurement light emitted from the optical comb light source unit 10 are assumed to have orthogonal planes of polarization. Components whose planes of polarization are orthogonal to each other may be mixed.

Further, the reference light reflected by the reference surface 25 and the measurement light reflected by the measurement object 50 are mixed by the light separation/mixing element 22B, and the mixed light is incident on the measurement photodetector 24. It has become so.

That is, the interference unit 20 detects the reference interference light obtained by causing the reference light and the measurement light to interfere with each other, both of which do not reciprocate the distance to the measurement object 50, by the reference photodetector 23. After obtaining the signal, the reference light that has reciprocated the distance L1 of the reference optical path to the reference plane 25 and the measurement light that has reciprocated the distance L2 of the measurement optical path to the measurement object 50 interfere with each other to obtain interference light for measurement. A measurement signal is obtained by detection by the measurement photodetector 24 . In the interference unit 20, the semitransparent mirror (BS), the polarizing beam splitter (PBS), the wave plate, the Faraday rotator, etc. are some of the components for generating the interference signal, and are necessary if the configuration of the interferometer changes. parts will also change.

In the interference section 20, the semitransparent mirror (BS), the polarizing beam splitter (PBS), the wave plate, the Faraday rotator, etc. are some of the components for generating the interference signal, and the configuration of the interferometer is not changed. The required parts will also change. The reference light and the measurement light do not interfere with each other in the orthogonally polarized states. Interference between the reference light and the measurement light is generated in some form, such as by including a function to differentially detect each and emphasize the interference signal.

In this optical comb distance measuring device 100, the time difference between the reference signal obtained by the reference photodetector 23 and the measurement signal obtained by the measurement photodetector 24 is the distance to the reference plane 25 on which the reference light makes a round trip. The delay time due to the light propagating a distance twice the absolute value (L2-L1) of the distance difference between the distance L1 of the reference optical path and the distance L2 of the measurement optical path to the measurement object 50 on which the measurement light traveled back and forth. The absolute value of the distance difference (L2-L1) is obtained by multiplying the speed of light C in vacuum and dividing by the refractive index _ng .

The signal processing unit 30 receives the state signal supplied from the state switching control unit 12 of the optical comb light source unit 10 in addition to the reference signal and the measurement signal supplied from the interference unit 20. are synchronously input to process the reference signal, the measurement signal and the state signal synchronously, thereby calculating the absolute value of the distance difference (L2-L1) and outputting it to the outside.

In the signal processing unit 30 in the optical comb distance measuring device 100, the reference signal and the By fetching measurement data in synchronization with the measurement signal, that is, the interference signal, and recording the waveform data by clarifying the waveform section (location) and the frequency setting state at that location, the frequency state in the waveform section to be processed can be determined. It is possible to confirm that the frequency setting has been completed and the state is stable, and that it is an effective section as waveform data. used for the conversion of

That is, the signal processing unit 30 synchronously captures the reference signal, the measurement signal, and the state signal, and simultaneously and correctly acquires the phase value obtained by the signal processing and the frequency setting of the signal section in which the phase value is output. As a result, distance calculation can be reliably performed in a short period of time while the location of the waveforms of the reference signal and the measurement signal and the frequency setting of the optical comb at that location are clearly grasped.

Here, the optical comb light source unit 10 in the optical comb distance measuring device 100 is cyclically modulated in intensity or phase, and N (N is an integer of 3 or more) types of modulation cycles are cyclically switched. It outputs M (M is an integer equal to or greater than 2) types of optical combs with different modulation cycles. M (M=2) types of modulated signals with different modulation periods, in which (N=4) types of modulation periods are cyclically switched, are provided in the optical comb light source section 10 (M=2). are given as drive signals F _mA and F _mB to the optical comb generators 11A and 11B, respectively, the intensity or phase is cyclically modulated, and N (N=4) types of modulation cycles are cyclically switched. In addition, M (M=2) types of optical combs having mutually different modulation periods are output from the optical comb generators 11A and 11B.

The state switching control unit 12 controls N (N=4) kinds of modulated signals F _m1 , F _m2 , F whose frequencies are fixed in phase synchronization with the reference frequency signal F _REF provided by the reference oscillator 4R and whose frequencies are different from each other. _N (N= ₄ ) kinds of modulated signals _Fm1 , Fm2, Fm3 from a modulated signal generator 4 having N (N=4) PLL oscillators 4A, 4B, 4C, _4D for generating m3, _Fm4 , _Fm4 are input, and switching of the selected output of the modulated signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 by the switch section 12A with N (N=4) inputs and M (M=2) outputs. A control section 12B for controlling is provided, and two types of modulation signals having mutually different modulation periods are supplied to the optical comb generators 11A and 11B as drive signals F _mA and F _mB via the switch section 12A. ing.

The first PLL oscillator 4A generates a first modulation signal fixed at a first frequency _fm ( _fm =25000 MHz) by being phase-locked by the PLL circuit to the reference frequency signal _FREF generated by the reference oscillator 4R. Generate F _m1 .

The second PLL oscillator 4B is phase-locked by the PLL circuit to the reference frequency signal F _REF generated by the reference oscillator 4R and fixed at a second frequency f _m +Δf _m (f _m +Δf _m =25010 MHz). A second modulated signal _Fm2 is generated.

The third PLL oscillator 4C is phase-locked by the PLL circuit to the reference frequency signal F _REF generated by the reference oscillator 4R and fixed at a third frequency f _m +Δf (f _m +Δf=25000.5 MHz). A third modulated signal _Fm3 is generated.

Furthermore, the fourth PLL oscillator 4D is phase-locked by the PLL circuit to the reference frequency signal F _REF generated by the reference oscillator 4R and fixed at a fourth frequency f _m +Δf (f _m +Δf+Δf _m =25010.5 MHz). to generate a modulated fourth modulated signal _Fm4 .

Incidentally, in the optical comb light source section 10 shown in the block diagram of FIG. N (N=4) types of modulated signals F _m1 , F _m2 , F _m3 and F _m4 are supplied from the modulated signal generating section 4 to the switch section 12A of the state switching control section 12 via isolators 5A, 5B, 5C and 5D. It is designed to be entered.

By inserting the isolators 5A, 5B, 5C and 5D in this way, the modulated signals F _m1 and F are generated from the modulated signal generator 12 to the switch section 12A of the state switching control section 12 via 5A, 5B, 5C and 5D. By inputting _m2 , _Fm3 , _{and Fm4} , it is possible to prevent the operation of the signal sources (PLL oscillators 4A, 4B, 4C, and 4D) from becoming unstable due to load fluctuations caused by the disconnection or release of circuits after the switch section 12A. can be prevented.

The isolators 5A, 5B, 5C, and 5D include isolation elements such as microwave amplifiers with large reverse isolation, π-type resistance attenuators, T-type resistance attenuators, microwave isolators using ferrite, and variable attenuators. and a band-pass filter, or an isolation circuit that combines an isolation amplifier with a resistance attenuator or a band-pass filter.

The switching operation of the switch section 12A of the state switching control section 12 is controlled by the control section 12B, so that the modulated signal generation section 4 inputs through the isolators 5A, 5B, 5C and 5D. The two optical comb generators 11A which cyclically switch the four types of modulated signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 and alternately output them from the two output terminals, and are connected to the two output terminals. , 11B as drive signals _FmA , _FmB , and cyclically switching four types of modulation signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 as shown in the transition state diagram of FIG. Acts as a switch.

Here, the control section 12B controls the 4-input 2-output switch section 12A with a 2-bit signal to select an output frequency. A 2-bit signal can be represented by a numerical value of 1 to 4, and the state of the light source section frequency setting can be output as a value of #1 to #4. Any one frequency of four types of modulation signals _Fm1 , _Fm2 , _{Fm3 ,} and _Fm4 appears in the driving signals FmA _{and FmB} . The two optical comb generators 11A and 11B are external modulation type optical comb generators that generate sidebands at frequency intervals matching the drive signals _{FmA and FmB or} at frequency intervals synchronized with the drive signals FmA _and FmB. It may also be a mode-locked laser light source in which the mode interval is a frequency interval that matches or is synchronized with the driving signals F _mA and F _mB .

The control unit 12B of the state switching control unit 12 in the optical comb distance measuring device 100 sets the transition states of the drive signals F _mA and F _mB to the two optical comb generators 11A and 11B as shown in Table 1 below. The switching operation of the switch section 12A is performed so as to cyclically switch the four types of modulation signals _Fm1 , _{Fm2 , Fm3} , and _Fm4 supplied to the optical comb generators 11A and 11B as drive signals FmA and _FmB . It controls and outputs a state signal indicating the switching state.

Table 1 shows the frequency transition states and phase differences of the drive signals F _mA and F _mB of the two optical comb generators 11A and 11B in settings #1 _to #4. For example, Δf = 500 kHz, Δf _m = 10 MHz, f _m = F _m1 (25000 MHz), f _m + Δf _m , where Δf _m is the required fundamental frequency shift and Δf is the driving frequency difference for generating the optical comb interference. =F _m2 (25010 MHz), f _m +Δf=F _m3 (25000.5 MHz), and f _m +Δf _m +Δf=F _m4 (25010.5 MHz).

That is, in this optical comb distance measuring device 100, the driving frequencies of the optical comb generators 11A and 11B are controlled by the driving signals _FmA and _FmB supplied to the two optical comb generators 11A and 11B. The transition is made by the unit 12 as shown in Table 2 below.

Here, in the optical comb distance measuring apparatus 100, reference light and measurement light having coherence pulsed and emitted from two optical comb generators 11A and 11B driven by two types of modulated signals with different frequencies are generated in principle. By using the signal processing unit 30, the interference signal obtained by the reference light detector 23, that is, the reference signal and the interference signal measurement signal obtained by the measurement photodetector 24 are converted into the state signal given by the state switching control unit 12. Then, frequency analysis is performed on the reference signal and the measurement signal based on the state signal, and the phase difference between the P-order modes of the reference signal and the measurement signal is calculated, where P is the mode number counted from the center frequency of the optical comb. After canceling the optical phase difference in the optical comb generation and transmission process from the optical comb generator to the reference point, the increment of the phase difference per order on the frequency axis is calculated to obtain the phase difference of the signal pulse. , the distance from the reference point to the measurement object plane 50 is calculated.

If the measured distance exceeds half the wavelength of the modulation frequency f _m , the periodicity of the object light makes the distance that is an integral multiple of the half wavelength unknown, and the distance cannot be uniquely determined. is measured four times using the reference light and the measurement light set to the four modulation frequencies shown in Table 1. In the signal processing section 30, the state signal and the reference light and measuring light, and using each phase difference obtained by performing the same processing, the distance exceeding the ambiguity distance (La=c/2f _m c: speed of light) corresponding to half the wavelength is calculated.

That is, the phase difference between the reference signal and the measurement signal obtained by setting the four modulation frequencies shown in Table 1 by the state switching control unit 12 and measuring is determined by the modulation for driving the two optical comb generators 11A and 11B. Setting #1, where the modulation frequencies of the signal are f _m and f _m +Δf, results in −2πf _m T, and setting #2, where the modulation frequencies of the modulation signal are f _m +Δf _m and f _m +Δf _m +Δf, −2π( f _m + Δf _m )T, and in setting #3 where the modulation frequencies of the modulation signal are fm + Δf and fm, −2π(f _m + Δf) T, and the modulation frequencies of the modulation signal are f _m + Δf _m + Δf and f _m + Δf _m In the setting of #4, it becomes −2π(f _m +Δf _m +Δf)T. The sign of the phase difference is corrected for sign reversal due to the reversal of the magnitude relationship of the modulation frequencies for driving the two optical comb generators 11A and 11B.

When longer than the distance (La = c/2f _m c: speed of light), the phase difference between the reference signal and the measurement signal (-2πf _m T) is of the form φ + 2mπ, where m is an integer, and by calculation only the φ part is is sought, but the integer value m is unknown.

On the other hand, the difference between the phase difference −2πf _m T between the reference signal and the measurement signal under setting #1 and the phase difference −2π(f _m +Δf _m )T between the reference signal and the measurement signal under setting #2 is 2πΔf _m T and the phase difference −2π(f _m +Δf)T between the reference signal and the measurement signal under setting #3 and the phase difference −2π(f _m +Δf _m +Δf) between the reference signal and the measurement signal under setting #4 )T is 2πΔf _m T, and the phase is uniquely determined up to the distance corresponding to the wavelength of 1/Δf _m (If Δf _m =10 MHz, La is 15 m).

Then, the integer m can be determined by multiplying this phase by f _m /Δf _m and comparing it with the phase difference of #1.

Furthermore, 2πΔfT is obtained from the difference between the phase difference −2πf _m T at setting #1 in Table 1 and the phase difference −2π(f _m +Δf)T at setting #3.

Furthermore, 2πΔfT is obtained from the difference between the phase difference −2π(f _m +Δf _m )T at setting #2 in Table 1 and the phase difference −2π(f _m +Δf _m +Δf)T at setting #4.

Here, when f _m =25 GHz, Δf=500 kHz, and Δf _m =10 MHz, since Δf=500 kHz, distance measurement up to La=300 m can be performed.

In the optical frequency comb distance measuring device 100, absolute distance measurement is performed using the reference signal and the measurement signal obtained by setting the four modulation frequencies shown in Table 1 by the state switching control unit 12 and measuring. That is, after holding one state for a certain period of time, it shifts to another state, measures the signal phase in that state in a certain interval, and uses the phases of the set states #1, #2, #3, and #4 to determine the absolute value. Execute the distance calculation process.

The measurement speed in this optical comb distance measurement device 100 is 500 kHz, which is equal to Δf for relative distance measurement within 6 mm, whereas for absolute distance measurement that requires frequency switching, the frequency switching time and the absolute distance calculation time are included. The four types of modulation signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 are cyclically switched by the state switching control unit 12 to change the drive states of the two optical comb generators 11A and 11B. The signal processing unit 30 takes in the reference signal, the measurement signal, and the state signal together with the state signal given by the control unit 12B of the state switching control unit 12, and converts the reference signal and the measurement signal into Absolute distance calculation can be performed reliably in a short time with a clear grasp of the location of the waveform and the frequency setting of the optical comb at that location.

That is, if the oscillation frequency of the PLL oscillator is switched and set in real time so as to obtain M types of modulation signals with mutually different modulation periods, the oscillation frequency can be switched and set freely. Absolute distance measurement in applications such as distance measurement to moving objects that require fast measurement processing due to the long settling time required to obtain a stable frequency signal at the desired frequency after being phase-locked at the set frequency. Although it takes time and is not practical, the optical frequency comb distance measuring device 100 reduces the absolute distance measurement time even for a moving object that needs to shorten the absolute distance measurement time as the moving speed increases. can be shortened and the absolute distance can be measured with high accuracy.

In this case, if only distance measurement up to 15 m is possible, it is possible to set only #1 and #2, or set only #3 and #4, but as described above, #1, #2, #3 , #4, that is, by cyclically switching the four types of modulated signals F _m1 , F _m2 , F _m3 , and F _m4 by the state switching control unit 12, the distance measurement range is extended to 300 m. , the absolute distance result can be obtained with high accuracy by correcting the phase offset due to the signal transmission path other than the measurement target. That is, when the modulation frequencies of the two optical comb generators 11A and 11B are exchanged, the phase derived from the distance to be measured does not change in absolute value but inverts its sign. On the other hand, the offset derived from the cable length of the interference signal transmission line has a constant value without changing the sign. Therefore, by subtracting the results of the two phase measurements and dividing by 2, the phase value excluding the offset can be obtained.

Here, the cyclical state transition is set such that when #1 is taken as a starting point, then #3, #2, #4, #2, #3, and then returns to #1. This setting also takes into account the result of measurement in which the frequencies of the driving signals F _mA and F _mB for driving the optical comb generator 11A and the optical comb generator 11B are exchanged, and the result of measurement in which the order of frequency exchange is reversed. By calculating the distance by using the distance calculation, the distance measurement error is minimized and the distance measurement is performed in the shortest time even while the object to be measured is moving at a high speed.

When performing two phase measurements to obtain a phase value excluding the phase offset, the order of switching the four modulation frequencies shown in Table 1 is arbitrary in principle, but #1→#2→#3→# 4→#4→#3→#2→#1, or #1→#3→#2→#4→#4→#2→#3→#1. By adopting a cyclic method in which continuous switching is performed in the reverse direction, it is possible to reduce distance measurement errors and measurement processing time.

In the absolute distance _measurement , _the distance is basically calculated with a set of four "transition states" of the frequency. Three types of modulation periods of _m + Δf and f _m + 2Δf are also possible, and in this optical comb distance measurement device 100, the intensity or phase is modulated periodically, and N (N is an integer of 3 or more) types of modulation periods An optical comb light source unit 10 that outputs M (M is an integer of 2 or more) types of optical combs that are cyclically switched and have mutually different modulation periods, and M types of drive signals that are phase-locked to a reference frequency signal. By providing a state switching control unit 12 for supplying to the comb light source unit 10 and controlling to output the M types of optical combs, the driving states of the two optical comb generators 11A and 11B can be rapidly changed. In the signal processing unit 30, the reference signal, the measurement signal, and the state signal are taken in together with the state signal given by the control unit 12B of the state switching control unit 12, and the positions of the waveforms of the reference signal and the measurement signal are obtained. Absolute distance calculation can be reliably performed in a short time while the frequency setting of the optical comb at the location is clearly grasped.

Here, FIG. 4 is a block diagram showing a specific configuration example of the 4-input 2-output switch section 12A of the state switching control section 12 incorporated in the optical comb light source section 10. As shown in FIG.

That is, as shown in the block diagram of FIG. 4, the 4-input 2-output switch portion 12A of the state switching control portion 12 has four types of signals generated by the PLL oscillators 4A, 4B, 4C, and 4D of the modulation signal generating portion 4. are input via isolators 13A, 13B, _{13C and 13D} into four one-input and two-output switch circuits 14 _{1A ,} 14 _1B and 14 _1C in the first stage. , 14 _1D , and the next stage to which the four types of modulation signals F _m1 , F _m2 , F _m3 , and F _m4 are inputted via the switch circuits 14 _1A , 14 _1B , 14 _1C , and 14 _1D of the first stage. Two switch circuits 14 _2A and 14 _2B each having 2 inputs and 1 output, and two switch circuits 14 having 1 input and 2 outputs connected to the respective output terminals of the two switch circuits 14 _2A and 14 _2B in the next stage. _3A , 14 _3B , and two switch circuits 14 _4A , 14 _4B with 2 inputs and 1 output at the final stage connected to the above two switch circuits 14 _3A , 14 _3B , respectively, are controlled by a control unit 12B comprising a control logic to control a reference frequency of 10 MHz. By switching control in synchronization with the signal F _REF , the transition states of the drive signals for the first and second optical comb generators 14A and 14B are changed as shown in FIG. The four types of modulation signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 supplied as drive signals to the comb generators 11A and 11B are cyclically switched.

In the switch section 12A, one of the two output terminals of the four first-stage switch circuits 14 _1A , 14 _1B , 14 _1C and 14 _1D is connected to the next-stage two switch circuits 14 _2A and 14 _2B . It is connected to the input terminal and the other output terminal is terminated by a terminating resistor.

Incidentally, in the specific example of the switch section 12A shown in the block diagram of FIG. 4, since it is composed of an isolator circuit combining a variable attenuator and a band-pass filter, the above-described switch section 12A is connected via the first to fourth 13A, 13B, 13C, and 13D. Four types of modulation signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 are input to four switch circuits _141A , _141B , _141C , and _141D in the first stage, and two switch circuits _144A , _144B in the final stage. The four types of modulated signals F _m1 , F _m2 , F _m3 , and F _m4 that are cyclically switched from the output terminals of the first and second isolators 15A each comprising an isolator circuit combining an isolation amplifier and a band-pass filter. , 15B.

Then, in this optical comb distance measuring device 100, the optical comb distance measuring method according to the present invention is carried out according to the procedure shown in the process diagram of FIG.

The optical comb distance measurement method according to the present invention is an optical comb distance measurement method for measuring the distance from the time difference between the interference signal between the reference light and the measurement light and the interference signal between the reference light and the measurement light that has passed through the measurement section. In the state switching step S1, the states of the modulation periods of one or more sets of measurement light and reference light whose intensity or phase is periodically modulated and whose modulation periods are different from each other are switched, and a state signal indicating the switching state is output. do. That is, in the optical comb light source unit 10, the state of each modulation cycle of the measurement light and the reference light emitted from the first and second optical comb generators 11A and 11B is set or switched by the state switching control unit 12. is read, and a state signal indicating the switching state is output.

In the next interference step S2, the measurement light and the reference light whose modulation period state has been switched in the state switching step S1 are caused to interfere with each other to generate reference interference light, and the measurement light whose modulation period state has been switched is generated. One of the light and the reference light is output toward the measurement object 50, and one of them interferes with the measurement light and the reference light that have reciprocated the distance to the measurement object 50 to generate interference light for measurement. do.

In the subsequent interference light detection step S3, the reference interference light and the measurement interference light generated in the interference step S2 are detected by the reference photodetector 23 and the measurement photodetector 24, thereby generating a reference signal and a measurement signal. is obtained and output.

That is, in the interference step S2, the distance L1 of the reference optical path to the reference plane 25 and the reference interference light obtained by interfering the reference light and the measurement light, both of which do not travel the distance to the measurement object 50, are Interference light for measurement is generated by interfering the reciprocating reference light and the measurement light traveling the distance L2 of the measurement optical path to the measurement object 50, and in the next interference light detection step S3, the reference photodetector 23 A reference signal and a measurement signal are obtained by detecting the reference interference light and the measurement interference light with the measurement photodetector 24 .

Then, in the next signal processing step S4, the distance to the measurement object 50 is calculated based on the reference signal and the measurement signal output in the interference light detection step S3 and the state signal output in the state switching step S1. calculate. That is, the signal processing unit 30 synchronously captures the state signal supplied from the state switching control unit 12 of the optical comb light source unit 10 in addition to the reference signal and the measurement signal supplied from the interference unit 20, By synchronizing and processing the reference signal, the measurement signal, and the state signal, the distance L1 of the reference optical path to the reference plane 25 along which the reference light reciprocates and the measurement optical path to the measurement object 50 along which the measurement light reciprocates. corresponds to the delay time due to the light propagating a distance twice the absolute value of the distance difference (L2-L1) of the distance L2, and the time difference between the reference signal and the measurement signal is multiplied by the speed of light C in vacuum The absolute value of the distance difference (L2-L1) is calculated by dividing by the refractive index _ng .

Here, in the signal processing step S3, as shown in the process diagram of FIG. The reference signal and the measurement signal output in S2 are taken in, and the phase difference between the envelope pulses of the reference signal and the measurement signal is calculated in the next phase difference calculation step S32. In the phase difference calculation step S32, when calculating the phase difference, the phase difference data is attached with the light source state of the signal section, ie, frequency information.

In the next distance calculation basic data acquisition step S33, one or more phase difference data of #1 to #4 given as examples of the state signal and the drive frequency are collected. At least one set of #1 and #2 or one set of #3 and #4 is required as the phase difference data to be collected in the distance calculation basic data acquisition step S32.

In the next order determination step S34, the difference between different states of the set of phase difference data collected in the distance calculation basic data acquisition step S33 is calculated. That is, the difference in phase difference is calculated. By this calculation, for example, in the case of #1 and #2 in the setting state shown in Table 1, the phase difference when measured by _Δfm is obtained. If _Δfm is 10 MHz, it will be a slow change of 2π [rad] at about 15 m. If the phase of _Δfm is expressed as φ _Δfm , and the phase of fm measured in setting state #1 is φ _fm , the value obtained by multiplying φ _Δfm by f _m /Δf _m is close to φ _fm +2Pπ (where P is the order). Since it should be a value, the order is determined from this relationship.

Then, in the next distance calculation step S35, φ _fm +2Nπ (N is the order) is divided by 2π and multiplied by half the wavelength of the fundamental frequency f _m , so that the distance represented by the optical distance is the measurement of the fundamental frequency f _m . The optical distance is obtained with high accuracy, and the obtained optical distance is subjected to refractive index correction and origin correction to obtain a distance output.

In this optical comb distance measuring device 100, by implementing the optical comb distance measuring method according to the present invention in this way, the frequency states of the measurement light and the reference light in the optical comb light source unit 10 that outputs the measurement light and the reference light Using the status signal that indicates, the measurement data is captured in synchronization with the interference signal, and the waveform section (location) and the frequency setting state at that location are clarified before recording the waveform data. There is no change in the frequency state in the interval, and it can be confirmed that the frequency setting has been completed and the state has stabilized, and it can be determined that the interval is valid as waveform data. Conversion to delay time or distance can be done reliably in a short time.

Here, a configuration example of the optical comb light source unit 10' provided with the external modulation type first and second optical comb generators 11A' and 11B' used as the optical comb light source unit 10 in the optical comb distance measuring device 100 is shown. It is shown in the block diagram of FIG.

In this optical comb light source unit 10', laser light emitted from a laser light source 1 is incident on external modulation type first and second optical comb generators 11A' and 11B' via an optical distributor 2. .

The first and second optical comb generators 11A' and 11B' generate four types of modulation signals _Fm1 , _Fm2 and _Fm3 generated by the PLL oscillators 4A, 4B, 4C and 4D of the modulation signal generator 4. , _Fm4 are cyclically selected via the switch section 12A of the state switching control section 12 and supplied as the drive signals FmA _{and FmB} , and _sideband signals are generated at frequency intervals synchronized with the drive signals FmA and _FmB . are periodically modulated in intensity or phase, and a pair of measurement light and reference light whose modulation periods are different from each other is emitted.

In the optical comb light source unit 10 in the optical comb distance measuring device 100, the state switching control unit 12 supplies four types of modulated signals F as drive signals F _mA and F _mB to the optical comb generators 11A and 11B. The control unit 12B controls the switching operation of the switch unit 12A so as to cyclically switch _m1 , Fm2, _{Fm3 ,} and _Fm4 , and outputs a state signal indicating the switching state. 8, the driving signals F _mA and F _mB whose modulation frequencies are cyclically switched by the switching control unit 12 are up-converted to generate the first and second optical combs. You may make it supply to the device 11A, 11B.

The optical comb light source unit 110 shown in FIG. 8 uses a frequency band of 1 GHz generated by the modulation signal generation unit 4 as a drive signal to be supplied to the two optical comb generators 11A and 11B in the optical comb light source unit 10 shown in FIG. The signals F ₁ , F ₂ , F ₃ and F ₄ are up-converted by frequency converters 7A and 7B to obtain modulated signals F _mA and F _mB of 25 GHz band.

The modulated signal generator 114 in the optical comb light source unit 110 includes four PLL oscillators 4A, 4B, 4C, and 4D that generate frequency signals F ₁ , F ₂ , F ₃ , and F ₄ in the 1 GHz band and 24 GHz frequency signals. It has one PLL oscillator 4E that generates _F0 .

In this optical comb light source unit 110, the fifth PLL oscillator 4E of the modulated signal generator 114 is phase-locked by the PLL circuit to the reference frequency signal _FREF supplied from the reference oscillator 4R, and the frequency _f0 is fixed at 24 GHz. is supplied via a power divider ₆ to two frequency converters 7A, 7B.

In the modulation signal generating section 114, the first PLL oscillator 4A is phase-locked by the PLL circuit to the reference frequency signal F _REF whose frequency is, for example, 10 MHz generated by the reference oscillator 4R, and the frequency is f _m '( generate a first frequency signal F ₁ fixed at f _m ′=1000 MHz).

The second PLL oscillator 4B is phase-locked by the PLL circuit to the reference frequency signal F _REF generated by the reference oscillator 4R, and its frequency is fixed at f _m '+Δf _m (f _m '+Δf _m =1010 MHz). A second frequency signal _F2 is generated.

The third PLL oscillator 4C is phase-locked by the PLL circuit to the reference frequency signal F _REF generated by the reference oscillator 4R, and its frequency is fixed at f _m '+Δf (f _m '+Δf=1000.5 MHz). generates a third frequency signal _F3 .

Further, the fourth oscillator 4D is phase-locked by the PLL circuit to the reference frequency signal F _REF generated by the reference oscillator 4R, and the frequency becomes f _m '+Δf _m +Δf (f _m '+Δf+Δf _m =1010.5 MHz). A fixed fourth frequency signal _F4 is generated.

In the modulated signal generator 114, the first to fourth frequency signals F ₁ , F ₂ , F ₃ and F 4 obtained by the first to fourth PLL oscillators 4A, 4B, 4C and _4D are generated by the isolator 5A. , 5B, 5C, and 5D to the 4-input 2-output switch section 12A of the state switching control section 12. FIG.

The control section 12B of the state switching control section 12 operates in synchronization with the reference frequency signal F _REF provided by the reference oscillator 4R of the modulation signal generation section 114 to generate the isolators 5A, 5B, 5C, 5A, 5B, 5C, The first to fourth frequency signals F ₁ , F ₂ , F ₃ , and F ₄ input to the four input terminals of the switch section 12A via 5D are cyclically switched to switch the two signals of the switch section 12A. The first and second modulated signals F _{ma and} F _mb obtained by cyclically switching four frequency signals F ₁ , F ₂ , F ₃ and F ₄ in the 1 GHz band, which are output from two output terminals, are converted to the above two frequencies. The switch section 12A functions as a 4-input 2-output selector switch for supplying power to the converters 7A and 7B.

Here, isolators 5A, 5B, 5C, and 5D are inserted between the modulated signal generating section 4 and the switch circuit 12A of the state switching control section 12, and the isolators 5A, 5B, 5C, By inputting the frequency signals F ₁ , F ₂ , F ₃ , and F ₄ to the switch circuit 12B via 5D, the operation of the signal source becomes unstable due to load fluctuations due to cutoff and release of the circuit after the switch circuit 12A. can be prevented from becoming

The isolators 5A, 5B, 5C, and 5D include isolation elements such as microwave amplifiers with large reverse isolation, π-type resistance attenuators, T-type resistance attenuators, microwave isolators using ferrite, and variable attenuators. and a band-pass filter, or an isolation circuit that combines an isolation amplifier with a resistance attenuator or a band-pass filter.

The first and second frequency converters 7A and 7B receive the frequency signal _F0 of the frequency (for example, 24 GHz) supplied from the fifth PLL oscillator 4E and the switch section of the state switching control section 12. Frequency signals F ₁ , F ₂ of four frequencies from 12A to 1 GHz, fm′=1000MHz, _fm ′+ _Δfm =1010MHz, fm _′ +Δf=1000.5MHz, fm′+Δfm _′ +Δf=1010.5MHz Using the first and second modulated signals Fma _{and Fmb} , which are cyclically switched to F3 _{and F4} and alternately output, _four types of modulation frequencies _fm =25000MHz and _fm + _Δfm in the 25 GHz band = 25010 MHz, f _m + Δf = 25000.5 MHz, f _m + Δf _m + Δf = 25010.5 MHz to obtain the first and second modulated signals F _mA and F _mB frequency-converted to obtain the first and second optical combs It is supplied as a drive signal to the generators 11A and 11B.

That is, the first and second frequency converters 7A and 7B convert the first and second modulated signals _Fma and _Fmb consisting of frequency signals _F1 , _F2 , _F3 and _F4 in the 1 GHz band to the above It functions as an up-converter for frequency-converting the first and second modulation signals F _mA and F _mB in the 25 GHz band which are supplied as drive signals to the first and second optical comb generators 11A and 11B.

The first and second frequency converters 7A and 7B are frequency mixers such as diodes, double-balanced mixers and IQ mixers, or frequency converters using phase synchronization having a configuration as shown in FIG. 7 is used.

Here, when frequency mixers such as diodes, double balanced mixers, and IQ mixers are used for the first and second frequency converters 7A and 7B, since the frequency mixers are nonlinear elements, #1 , #2, #3, and #4 generate frequency components other than the necessary frequency components ( _fm , _fm + _Δfm , _fm +Δf, _fm + _Δfm +Δf). By inserting band-pass filters 8A and 8B at the output sides of the frequency converters 7A and 7B, respectively, only necessary frequency components are supplied as drive signals to the optical comb generators 11A and 11B.

For example, in the first frequency converter 7A using a frequency mixer, for example, in the case of setting #1, not only the required fm frequency component but also the unwanted frequency component f _m +Sf _b (except for S=0) Spurious occurs. Here, S is an integer and _fb is the frequency of the modulated signal before frequency conversion input to the frequency mixer 23A. If this frequency component is mixed in the first modulation signal _FmA supplied as a drive signal to the first optical comb generator 11A, it becomes spurious in the optical comb generation by the first optical comb generator 11A, resulting in a measured value. may have an impact. To avoid this effect, a band-pass filter 8A is used to pass only the necessary _fm frequency component and attenuate other frequency components to the extent that the measurement specifications are not affected.

Moreover, the unwanted frequency component f _m +Sf _b generated by the first frequency converter 7A using a frequency mixer also propagates in the direction of the power divider 6 on the input side, and the power divider 61 also has ideal characteristics. , it reaches the second frequency converter 7B. By frequency-converting the unwanted frequency component f _m +Sf _b that has reached the second frequency converter 7B, the output of the second frequency converter 7B has f _m +Sf _b +S′(f _b +Δf ) is mixed. Here, (f _b +Δf) is the frequency of the modulated signal before frequency conversion input to the frequency converter 7B.

where S' is an integer. Since frequency components other than S+S'=0 are out of f _m to +f _b or -f _b , they can be attenuated by the band-pass filter 8A that passes the required frequency of f _m +Δf. However, the frequency component of S+S′=0 becomes f _m +S′Δf, a frequency component very close to the required f _m +Δf _m of S′=1, which is difficult to remove by bandpass filter 24A, but the input By inserting the isolators 5E and 5F on each side, it is possible to attenuate the reflected components by the frequency converters 7A and 7B.

The isolators 5E and 5F include isolation elements such as microwave amplifiers with large reverse isolation, pi-shaped resistance attenuators, T-shaped resistance attenuators, microwave isolators using ferrite, variable attenuators and band-pass filters. or an isolation circuit combining an isolation amplifier with a resistance attenuator or a band-pass filter.

In the optical comb light source unit 110, for practical purposes, an optimum structure is adopted in which these are combined to improve the performance.

In the optical comb light source unit 110, if f _b and f _b +Δf are set to about 100 MHz _, an improvement in relative phase noise of 40 dB or more can _be expected. The pass filters 8A and 8B require filters with a very high Q value of 2500 or more to reduce the spurious of f _m +f _b or f _m -f _b .

Here, the frequency converters 7A and 7B are not frequency mixers such as diodes, double-balanced mixers, and IQ mixers, but frequency converters 7 using phase synchronization having the configuration shown in FIG. can also

The frequency converter 7 includes a phase comparator 71, a voltage-controlled oscillator 72 whose oscillation phase is controlled by the phase comparator 71, and a frequency signal output from the voltage-controlled oscillator 72. A frequency mixer 73 is provided.

In this frequency converter 7, a modulated signal F _b having a modulated frequency f _b in the 100 MHz band is input to a phase comparator 71, and a frequency signal having a frequency of f _m −f _b of 24.9 GHz is output from the fifth PLL oscillator 4E. is supplied to the frequency mixer ₇₃ . The frequency mixer 73 obtains the frequency signal of the difference frequency f _b ' between the modulation signal F _m of the 25 GHz band modulation frequency f _m output from the voltage-controlled oscillator 72 and the frequency signal F0 of the 24.9 GHz band. By controlling the oscillation phase of the voltage-controlled oscillator 72 with the phase comparison output obtained by phase-comparing the modulation signal Fb of the 100 MHz band modulation frequency _{f b with} the phase comparator 71, the modulation frequency of the 100 MHz band is obtained. The voltage-controlled oscillator 72 outputs a modulated signal _Fm with a modulated frequency _fm in _the 25 GHz band whose frequency is fixed in phase synchronization with the modulated signal Fb of _fb .

That is, when the frequency converter 7 is used as the frequency converter 7A, for example, the phase comparator 71 receives four frequency signals F ₁ , F _{2 ,} F 100 MHz from the switch section 12A of the state switching control section 12. By supplying the first modulated signal F _ma obtained by cyclically switching between F ₃ and F ₄ , the frequency signal of the difference frequency f _b ′ and the first modulated signal F _ma are phase-compared to obtain the The voltage-controlled oscillator 72 is fed back to control the oscillation phase of the voltage-controlled oscillator 72 to up-convert the first modulated signal _Fma of 100 MHz band to obtain a modulated signal F _mA of frequency f _mA of 25 GHz band. It can be output from the voltage controlled oscillator 72 .

When the frequency converter 7 is used as the frequency converter 7B, for example, the phase comparator 71 receives four frequency signals F ₁ , F ₂ , F 100 MHz from the switch section 12A of the state switching control section 12. By supplying the second modulated signal F _mb obtained by cyclically switching between F ₃ and F ₄ , phase comparison is performed between the frequency signal of the difference frequency f _{b ′} and the second modulated signal F _mb . The voltage-controlled oscillator 72 is fed back to control the oscillation phase of the voltage-controlled oscillator 72, and the second modulated signal Fmb of the 100 MHz band is up-converted to produce the modulated _{signal FmB} of the frequency fmB of the 25 GHz band. It can be output from the voltage controlled oscillator 72 .

Here, in the frequency converter 7, the phase comparator 71 is a phase comparator such as a double balanced mixer, and has low noise because it performs phase comparison between the same frequencies. Further, since frequency comparison is performed at a frequency in the 100 MHz band of the modulation frequency _fb , the control band can be widened, for example, 10 MHz or more. Therefore, the relative phase noise of the outputs of the frequency converters 7A and 7B is the relative phase noise of the signals with the modulation frequencies f _b and f _b +Δf _m in the 100 MHz band. Furthermore, since the control band of the PLL is wide, the settling time required to obtain a stable frequency signal at the target frequency can be shortened.

In addition, since the output of the frequency converter 7 is sufficiently larger than the phase synchronization control band of the signal with the modulation frequency f _b or f _b +Δf in the 100 MHz band, the spurious f _m +f _b or the spurious f _m − of the voltage controlled oscillator 72 f _b can be made small.

Therefore, by using the frequency converters 7 using phase synchronization as the frequency converters 7A and 7B, the band-pass filters 8A and 8B on the output side can be eliminated or the specifications can be reduced.

In the optical comb distance measuring device 100, the driving signals F _mA and F _mA whose modulation frequencies are cyclically switched by the switching control unit 12 are up-converted by the frequency converters 7A and 7B to obtain the first and second signals. Distance measurement can be performed using the low relative phase noise optical comb emitted from the optical comb generator 110 supplied to the optical comb generators 11A and 11B as reference light and measurement light.

Further, in the optical comb light source units 10 and 110, the phase-locked reference frequency signal F _REF provided by the reference oscillator 4R generated by the modulation signal generating units 4 and 114 is phase-locked with an integer N of 3 or more having mutually different oscillation frequencies. The types of modulated signals are cyclically switched by the N input M (M is a positive integer) output switch section 12A of the state switching control section 12, and M types of modulated signals having different modulation periods are used as driving signals. Although the optical comb generator of 1 is made to output M types of optical combs, like the state switching control unit 112 in the optical comb light source unit 120 shown in FIG. 10, N types of optical combs with different modulation periods are generated M types of optical combs with mutually different modulation cycles are generated from N types of optical combs generated by N optical comb generators 11A, 11B, . . . The control unit 112B controls the switching selection operation of the switch unit 112A using the N-input M-output optical switch so as to cyclically select and output, and a state signal indicating the switching selection state is sent from the control unit 112B. may be output.

In this case, it is not necessary for all the optical combs to have different modulation periods, and some of them can be used for different switching even if they have the same modulation period, such as different wavelengths. It is essential to include a set of optical combs in the same wavelength band with different modulation periods in order to take interference, but even if the combination of the same modulation period includes optical combs in different wavelength bands, it will still function. do.

Here, with N=4 and M=2, the optical comb light source unit 120 includes four optical comb generators 11A, 11B, 11C, and 11D and a reference frequency signal F _REF generated by a reference oscillator 4R. a modulated signal generator 4 having four PLL oscillators 4A, 4B, 4C, and 4D for generating N (N=4) kinds of synchronized modulated signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 ; A state switching control unit 112 is provided for cyclically selecting and outputting two types of optical combs having mutually different modulation periods from four types of optical combs generated by the optical comb generators 11A, 11B, 11C, and 11D.

The four optical comb generators 11A, 11B, 11C and 11D are N( By being driven by N=4) types of modulation signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 , four types of optical combs having mutually different modulation periods are generated.

The four optical comb generators 11A, 11B, 11C, and 11D may be of the external modulation type that generate sidebands at frequency intervals matching the frequencies of the modulated signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 . Alternatively, it may be a mode-locked laser light source in which the mode intervals are intervals of frequencies that match or are synchronized with the frequencies of the modulated signals _Fm1 , _Fm2 , _Fm3 , and _Fm4 .

Then, the state switching control section 112 cyclically selects two types of optical combs having mutually different modulation periods from the four types of optical combs generated by the four optical comb generators 11A, 11B, 11C, and 11D. and a control unit 112B for controlling the selection operation of the optical comb by the switch unit 112A using the 4-input 2-output optical switch and the above-mentioned control unit 112B. The switch unit 112A using the 4-input 2-output optical switch controlled by the unit 112B outputs two types of optical combs by cyclically selecting four types of optical combs having mutually different modulation cycles and frequencies. A state signal indicating the selection state of the optical comb by the switch section 112A using an optical switch is output.

Since the optical comb light source section 120 switches the optical comb, it is not necessary to switch the modulation signals having different modulation periods generated by the modulation signal generation section 4 .

Here, in the optical comb distance measuring device 100, the reference signal and the measurement signal are obtained by the reference photodetector 23 and the measurement photodetector 24 provided in the interference unit 20, but the reference light By using an optical fiber for the light guiding portion to the detector 23 and the measuring photodetector 24, the reference photodetector can be connected to the signal processing unit 30A as in the optical comb distance measuring device 100A shown in the block diagram of FIG. 23. A measuring photodetector 24 may be provided.

In this optical comb distance measuring device 100A, the interference unit 20A uses the reference light detector 23 and the measurement light detector 24 provided in the signal processing unit 30A to obtain the reference signal and the measurement light. The generated reference interference light and measurement interference light are sent to a reference photodetector 23 and a measurement photodetector 24 provided in the signal processing unit 30A through two optical fibers. 123 and 124 to make the light incident thereon.

In the signal processing unit 30A in the optical frequency comb distance measuring device 100A, the frequency state of the optical frequency comb light source unit 10 is switched by the state switching control unit 12 built in the optical comb light source unit 10, and a state signal indicating the switching state is captured. By synchronizing and processing the reference signal, the measurement signal, and the state signal obtained by the reference photodetector 23 and the measurement photodetector 24, the reference optical path to the reference plane 25 on which the reference light travels back and forth can be determined. Corresponds to the delay time due to the light propagating a distance twice the absolute value (L2-L1) of the distance difference between the distance L1 and the distance L2 of the measurement optical path to the measurement object 50 on which the measurement light travels, The absolute value of the distance difference (L2-L1) is calculated by multiplying the time difference between the reference signal and the measurement signal by the speed of light C in a vacuum and dividing by the refractive index _ng .

The installation positions of the reference photodetector 23 and the measurement photodetector 24 are arbitrary, and they may be included in the optical comb light source section 10 .

Further, in the optical comb distance measuring devices 100 and 100A, the state switching control section 12 is incorporated in the optical comb light source section 10, but the control section 12B of the state switching control section 12 It need not be built in, and may be installed in the signal processing unit 30B like the optical comb distance measuring device 100B shown in the block diagram of FIG.

This optical comb distance measurement device 100B is obtained by moving the control unit 12B of the state switching control unit 12 to the signal processing unit 30A in the optical comb distance measurement device 100A. A reference photodetector 23 and a measurement photodetector 24 to which the reference interference light and the measurement interference light are incident via two optical fibers 123 and 124 are provided. is provided with a control unit 12B. When the reference photodetector 23 and the measurement photodetector 24 for differentially detecting orthogonal projection components are used, the reference interference light and the measurement interference light are separated into two orthogonal polarized light beams. Thus, the light is incident on the reference photodetector 23 and the measurement photodetector 24 via two optical fibers for each, four optical fibers in total.

In this optical comb distance measuring device 100B, the state switching control unit 12 controls the operation of the switch unit 12A on the side of the optical comb light source unit 10 from the control unit 12B provided in the signal processing unit 30B. 10B, the signal processing unit 30B takes in a state signal indicating the switching state, and synchronizes the reference signal and the measurement signal obtained by the reference photodetector 23 and the measurement photodetector 24 with the above state signal. The absolute value ( L2-L1) corresponds to the delay time due to the light propagating a _distance twice as large as L2-L1). The absolute value of the distance difference (L2-L1) is calculated.

In the optical comb distance measuring devices 100A and 100B, the signal processing units 30A and 30B generate state signals indicating the frequency states of the measurement light and the reference light in the optical comb light source units 10 and 10B that output the measurement light and the reference light. is used to acquire measurement data in synchronization with the reference signal and the measurement signal, that is, the interference signal, and record the waveform data by clarifying the waveform section (location) and the frequency setting state at that location. There is no change in the frequency state in the waveform section, the completion of the frequency setting and the stability of the state can be confirmed, and it can be judged that the section is valid as waveform data. Conversion from value to delay time or distance can be done reliably in a short time.

In the interference units 20, 20A, and 10B of the optical comb distance measuring devices 100, 100A, and 100B, the reference plane 25 is provided in the reference optical path of the distance L1 through which the reference light passes. Alternatively, a retroreflector or an optical fiber may be used to form the distance L1 of the reference optical path.

1 laser light source, 2 optical distributor, 4 modulation signal generator, 4R reference oscillator, 4A to 4E PLL oscillator, 5A to 5F, 13A to 13D, 15A, 15B isolator, 7, 7A, 7B frequency converter, 8A, 8B Bandpass filters 10, 10', 10B, 110, 120 Optical comb light source section 11A to 11D, 11A', 11B' Optical comb generator 12 112 State switching control section 12A, 112A Switch section 12B, 112B Control section, 14 _1A , 14 _1B , 14 _1C , 14 _1D , 14 _2A , 14 _2B , 14 _3A , 14 _3B , 14 _4A , 144 _4B switch circuit, 20, 20A interference section, 21 total reflection mirror, 22A light mixing element, 22B light separation/mixing element, 23 reference light detector, 24 measurement light detector, 25 reference plane, 26A, 26B quarter wave plate, 30, 20A, 30B signal processing unit, 71 phase comparator, 72 voltage controlled oscillator , 73 frequency mixer, 100, 100A, 100B optical comb distance measuring device

Claims (8)

An optical comb distance measurement method for measuring a distance from the time difference between the interference signal of the reference light and the measurement light, in which one of the interference signals of the reference light and the measurement light passes through the measurement section,
a state switching step of switching the state of the modulation cycle of one or more pairs of measurement light and reference light, each of which is periodically modulated in intensity or phase and has different modulation cycles, and outputting a state signal indicating the switching state;
In the state switching step, the measurement light whose modulation period state has been switched and the reference light are caused to interfere with each other to generate reference interference light, and either the measurement light or the reference light whose modulation period state has been switched is generated. toward the object to be measured, and one of them interfering the interference light of the measurement light and the reference light, which have reciprocated the distance to the object to be measured, to generate interference light for measurement;
an interference light detection step of obtaining a reference signal and a measurement signal by detecting the reference interference light and the measurement interference light generated in the interference step;
and a signal processing step of calculating the distance to the object to be measured based on the reference signal and the measurement signal obtained in the interference light detection step and the state signal output in the state switching step. Optical comb distance measurement method. In the state switching step, X (integer of 3 or more) input Y (Y is a positive integer) output of X (integer of 3 or more) input through at least 3 isolators of N types of modulated signals of 3 or more integers having different frequencies Switching control is performed to selectively output the N types of modulated signals to M (M is a positive integer) optical comb generators of the optical comb light source unit via the switch unit, and the switch unit selects 2. A state signal indicating a switching state of the modulation periods of the measurement light and the reference light emitted from the M optical comb generators is output according to the selection state of N types of modulation signals. The optical comb distance measurement method described in . In the state switching step, at least two frequency converters to which a frequency signal obtained by one oscillator of the modulated signal generator provided with three oscillators is input are fed by oscillators other than the one oscillator of the modulated signal generator. Each of the obtained frequency signals is switched by a switch unit to be input, and at least two types of modulated signals having different frequencies frequency-converted by the at least two frequency converters are generated by at least two optical combs of the optical comb light source unit. and a modulation cycle of the measurement light and the reference light emitted from the at least two optical comb generators according to the switching state of each frequency signal switched input to the two frequency converters. 3. The optical comb distance measuring method according to claim 2, wherein a state signal indicating the switching state of is output. In the state switching step, from the N types of optical combs generated by the N optical comb generators of the optical comb light source section, M types of light beams having different modulation periods are passed through a switch section using an optical switch. 2. The optical comb distance measuring method according to claim 1, wherein selection control is performed to cyclically select and output combs, and a state signal indicating the selected state is output. An optical comb distance measuring device that measures a distance from the time difference between the interference signal of the reference light and the measurement light, in which one of the interference signals of the reference light and the measurement light passes through the measurement section,
an optical comb light source unit that outputs one or more pairs of measurement light and reference light whose intensity or phase is modulated periodically and whose modulation periods are different from each other;
a state switching control unit that switches the state of the modulation period of the measurement light and the reference light output from the optical comb light source unit and outputs a state signal indicating the switching state;
Measurement light and reference light are input from the optical comb light source unit, the input measurement light and reference light are interfered to generate reference interference light, and one of the input measurement light and reference light is generated. an interference unit that outputs toward a measurement object and causes interference between the measurement light and the reference light, one of which has reciprocated the distance to the measurement object, to generate interference light for measurement;
a reference photodetector that detects the reference interference light generated by the interference unit and outputs a reference signal;
a measurement photodetector that detects the interference light for measurement generated by the interference unit and outputs a measurement signal;
Calculate the distance to the measurement object based on the reference signal output from the reference photodetector, the measurement signal output from the measurement photodetector, and the state signal output from the state switching control unit. An optical comb distance measuring device comprising: a signal processing unit for The optical comb light source unit includes M (M is a positive integer) optical comb generators, and N types of modulation with an integer of 3 or more different frequencies are selectively input via the state switching control unit. M types of optical combs whose intensity or phase is periodically modulated by at least three kinds of modulated signals among the signals and whose modulation periods are different from each other are used as the measurement light and the reference light whose modulation period state is switched. output and
The state switching control section includes an X (integer of 3 or more) input Y (Y is a positive integer) output switch section to which the N types of modulated signals are input via at least three isolators, and the switch section. to selectively output the N kinds of modulated signals to the M optical comb generators of the optical comb light source unit, and the selection state of the N kinds of modulated signals selected by the switch unit 6. The optical comb distance measuring device according to claim 5, wherein a state signal indicating the switching state of the modulation periods of the measurement light and the reference light emitted from the M optical comb generators is output according to . a modulated signal generator comprising at least three oscillators that generate frequency signals having different frequencies;
At least two frequency converters to which frequency signals obtained by one of the three oscillators of the modulation signal generator and frequency signals obtained by oscillators other than the one oscillator are input,
The state switching control unit switches each frequency signal obtained by each oscillator other than the one oscillator by the switch unit to input it to the at least two frequency converters, and frequency-converted by the at least two frequency converters. At least two types of modulated signals having different frequencies are supplied as drive signals to at least two optical comb generators of the optical comb light source unit, and switching between frequency signals to be switched and input to the two frequency converters. 7. The optical comb distance measurement according to claim 6, wherein a state signal indicating a switching state of the modulation periods of the measurement light and the reference light emitted from the at least two optical comb generators is output according to the state. Device. The optical comb light source unit includes N optical comb generators each of which is periodically modulated in intensity or phase and generates N kinds of optical combs of integers equal to or greater than 3 with mutually different modulation cycles,
The state switching control section cyclically selects M (M is a positive integer) types of optical combs having mutually different modulation cycles from the N types of optical combs generated by the N optical comb generators of the optical comb light source section. A switch unit using an optical switch that selectively outputs an output, and a control unit that controls the selection operation of the optical comb by the switch unit using the optical switch. Selective control is performed to cyclically select and output M types of optical combs with different modulation cycles from N types of optical combs via a switch unit, and a state signal indicating the selection state is output. 6. The optical comb distance measuring device according to claim 5.

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