Non-contact distance measuring device and method

Abstract

To realize the extension of measured distance without lowering a frequency sweep speed in a simple distance measuring device that uses a single light source.SOLUTION: The present disclosure pertains to a contactless distance measuring device that irradiates a measurement object with frequency sweep light and measures the frequency of a beat signal due to the interference of probe light reflected by the measurement object with reference light, thereby finding a distance to the measurement object. The contactless distance measuring device comprises a light replication unit that the reference light or the probe light enters and that replicates light of a plurality of different frequencies from the incident light, and main interferometer that multiplexes the light of the plurality of frequencies and the reference light or the probe light that did not enter the replication unit and detects a smallest beat frequency that is obtained by interference of the light of the plurality of frequencies with the reference light or the probe light that did not enter the light replication unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a non-contact distance measuring device and method using frequency swept light. [Background technology]

[0002] Accurate distance measurement technology is an important technology for measurements such as measuring the shape of large-scale structures. There are many such applications, including measuring the shape of artificial objects such as parabolic antennas and buildings, and measuring natural formations such as ice sheet thickness and forest height. In particular, there is a demand for high-precision measurement of the position and shape of distant objects in large-scale structure measurements for building health monitoring and disaster prevention purposes.

[0003] LiDAR (Light Detection And Ranging) is a non-contact distance measurement technology that uses laser light to measure the optical path length to the object being measured. Among these technologies, frequency modulated continuous wave (FMCW) LiDAR measures distance using a single light source and is capable of detecting speed and vibration. FMCW LiDAR sweeps the optical frequency and converts the frequency difference (beat frequency, IF) that occurs due to interference with the returned light into distance. Using a light source with a 100nm sweep bandwidth, a resolution of approximately 12μm can be achieved.

[0004] However, with FMCW LiDAR, the measurement distance is limited to several tens of meters due to the coherence length of the light source. Furthermore, measurements cannot be made where the resulting beat frequency exceeds the reception bandwidth. This means that, as long as the reception bandwidth is constant, there is an upper limit to the product of the frequency sweep rate and the measurement distance. In other words, if the reception bandwidth is constant, there is a problem in that either the measurement distance or the frequency sweep rate must be sacrificed. Furthermore, since the measurement repetition frequency (refresh rate) is proportional to the frequency sweep rate, sacrificing the frequency sweep rate also means sacrificing the refresh rate. Due to these two factors, FMCW LiDAR has been limited to measuring relatively short distances, typically within several tens of meters. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] T. Sakamoto et al. “Asymptotic formalism for ultraflat optical frequency comb generation using a Mach-Zehnder modulator,” OPTICS LETTERS Vol. 32, No. 11 p.1515 June 1, 2007 [Non-patent document 2] F. Ito et al., “Long-Range Coherent OFDR with Light Source Phase Noise Compensation,” JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 8, pp. 1015-1024, APRIL 15, 2012 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above problem, an object of the present disclosure is to realize an extension of the measurement distance without reducing the frequency sweep speed in a simple distance measuring device using a single light source. [Means for solving the problem]

[0007] To achieve the above object, the present disclosure replicates light of multiple frequencies from either a reference light or a probe light, and causes the replicated light of multiple frequencies to interfere with the other of the reference light or the probe light.

[0008] Specifically, the non-contact distance measuring device according to the present disclosure includes: 1. A non-contact distance measuring device that irradiates a frequency sweep light onto an object to be measured, and measures the frequency of a beat signal generated by interference between a probe light and a reference light reflected by the object to determine a distance to the object, an optical duplication unit that receives the reference light or the probe light and duplicates the incident light into light of a plurality of different frequencies; a main interferometer that combines the light of the plurality of frequencies and the reference light or the probe light that has not been input to the duplication unit, and detects a minimum beat frequency obtained by interference between the light of the plurality of frequencies and the reference light or the probe light that has not been input to the optical duplication unit; Equipped with.

[0009] Specifically, the non-contact distance measuring method according to the present disclosure includes: 1. A non-contact distance measuring method for determining a distance to an object to be measured by irradiating the object with frequency sweep light and measuring a frequency of a beat signal generated by interference between a probe light reflected by the object and a reference light, comprising: replicating the reference light or the probe light into light of different frequencies; combining the light of the plurality of frequencies and the unduplicated reference light or the unduplicated probe light, and detecting a minimum beat frequency obtained by interference between the light of the plurality of frequencies and the unduplicated reference light or the unduplicated probe light; Do the following. [Effects of the Invention]

[0010] According to the present disclosure, in a simple distance measuring device using a single light source, it is possible to extend the measurement distance without reducing the frequency sweep speed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating an example of the configuration of a non-contact distance measuring device according to a first embodiment. [Figure 2] 1A and 1B are diagrams illustrating the frequencies of reference light and probe light and the interference signal spectrum in a conventional FMCW LiDAR. [Figure 3] 4 is a diagram illustrating the frequencies of a reference light and a probe light in the non-contact distance measuring device according to the first embodiment. FIG. [Figure 4]FIG. 3 is a diagram illustrating an interference signal spectrum in the non-contact distance measuring device according to the first embodiment. [Figure 5] 4 is a diagram illustrating the frequencies of a reference light and a probe light in the non-contact distance measuring device according to the first embodiment. FIG. [Figure 6] 4 is a diagram illustrating the frequencies of a reference light and a probe light in the non-contact distance measuring device according to the first embodiment. FIG. [Figure 7] FIG. 10 is a diagram illustrating an example of the configuration of a non-contact distance measuring device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0013] (Embodiment 1) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Figure 1 shows an embodiment of the present disclosure based on a FWCW-type LiDAR system. 1 denotes a frequency swept light source, 2 a coupler that multiplexes or demultiplexes light, 3 an optical circulator, 4 a lens, 5 an object to be measured, 6 a delay device, 7 an optical frequency comb generator, 8 an optical 90-degree hybrid, 9 a balanced photodetector, 10 an AD converter, 11 an arithmetic unit such as a computer, and 12 an RF synthesizer.

[0014] The optical frequency comb generator 7 functions as an optical duplication unit in this disclosure. The optical 90-degree hybrid 8, balanced photodetectors 9-1 and 9-2, and AD converter 10-1 constitute a main interferometer 20 that functions as an optical detection unit in this disclosure. Hereinafter, the "reception band of the optical detection unit" will be abbreviated as the "reception band."

[0015] The frequency sweep light source 1 oscillates a laser beam whose frequency is linearly modulated. The frequency is swept over a frequency sweep width ΔF at a constant sweep speed γ [Hz / s] for a constant frequency sweep time ΔT. In this embodiment, the light output from the frequency sweep light source 1 is described as laser beam, but is not limited to this as long as it is coherent light.

[0016] Coupler 2-1 splits the light input from frequency sweep light source 1 into two, and inputs one of the beams to optical circulator 3 as probe light and the other to optical frequency comb generator 7 as reference light. Optical circulator 3 inputs the probe light from coupler 2-1 to lens 4. Optical circulator 3 also inputs the light from lens 4 to optical 90-degree hybrid 8. Lens 4 converts the probe light from frequency sweep light source 1 into a plane wave. Lens 4 also collects the probe light reflected from device under test 5 and inputs it to optical circulator 3.

[0017] The optical frequency comb generator 7 generates high-order modulation sidebands from the input light. A specific configuration of the optical frequency comb generator 7 is described in, for example, Non-Patent Document 1. In this embodiment, as an example, a signal from an RF synthesizer 12 via an amplifier 13 is input to the optical frequency comb generator 7, and the optical frequency comb generator 7 generates an optical frequency comb at a frequency interval corresponding to the signal from the RF synthesizer 12.

[0018] The optical frequency comb generator 7 generates an optical frequency comb consisting of multiple different frequencies, including the frequency of the reference light input from the coupler 2-1. The optical frequency comb generator 7 inputs the generated optical frequency comb to the optical 90-degree hybrid 8 as the reference light for the main interferometer 20. The probe light reflected by the object under test 5 interferes with the laser light (reference light) in the optical 90-degree hybrid 8 (main interferometer). The main interferometer 20 can measure the delay time of the probe light reflected from the object under test 5 relative to the reference light. The calculation unit 11 performs distance measurement using this delay time. In FIG. 1, the calculation unit 11 is configured to be included in the main interferometer 20, but the main interferometer 20 and the calculation unit 11 may be separate.

[0019] Specifically, the optical 90-degree hybrid 8 generates an in-phase component I of a beat signal by combining the reference light and the light reflected from the object under test 5, and inputs this to a balanced photodetector 9-1. The optical 90-degree hybrid 8 also generates a quadrature component Q of a beat signal by combining the reference light, which has been phase-shifted by 90 degrees, and the light reflected from the object under test, and inputs this to a balanced photodetector 9-2.

[0020] The balanced photodetector 9-1 acquires an analog electrical signal of the in-phase component I of the beat signal based on the input from the optical 90-degree hybrid 8 and inputs it to the AD converter 10-1. The balanced photodetector 9-2 acquires an analog electrical signal of the quadrature component Q of the beat signal based on the input from the optical 90-degree hybrid 8 and inputs it to the AD converter 10-1. The AD converter 10-1 converts the analog electrical signal of the in-phase component I of the beat signal input from the coupler 9-1 and the analog electrical signal of the quadrature component Q of the beat signal input from the coupler 9-2 into digital signals and inputs them to the calculation unit 11.

[0021] Here, we will explain the interference between the reference light and the probe light in a conventional FMCW LiDAR that does not have an optical frequency comb generator 7, using Figure 2. That is, in a conventional FMCW LiDAR, the reference light from coupler 2-1 is directly input to the optical 90-degree hybrid 8 in the main interferometer of Figure 1. In a conventional FMCW LiDAR, the reference light from coupler 2-1 and the probe light, which is delayed by the distance from the reference light to the object under test 5 and back, arrive, generating a beat signal with a frequency corresponding to the frequency difference. Hereinafter, the frequency of the beat signal is referred to as the beat frequency IF. This beat frequency IF is proportional to the delay time of the probe light reflected from the object under test 5 relative to the reference light, enabling distance measurement.

[0022] Specifically, the beat signal is expressed as a complex number using the I-phase component and the Q-phase component of the beat signal output from the optical 90-degree hybrid 8, as shown in equation (1). (Number 1) I+jQ=exp(jγτt) (1)

[0023] The calculation unit 11 calculates the phase of the beat signal from equation (1) based on the in-phase component I and quadrature component Q of the hybrid signal input from the AD converter 10-1, where τ is the delay time of the probe light relative to the reference light, which corresponds to the optical path difference between the reference light and the probe light, and γτ is the beat frequency IF.

[0024] In general, the distance resolution Δz of an FMCW LiDAR is expressed as follows using the frequency sweep width ΔF: (Number 2) Δz=c / (2ΔF) (2)

[0025] In other words, to improve the distance resolution Δz, the frequency sweep width ΔF must be increased. Furthermore, the beat frequency IF is proportional to the delay time τ, which varies depending on the distance to the object 5, and the sweep rate γ. Therefore, if the reception band is constant, there will be a limit to the product of the sweep rate γ and the distance. Specifically, as shown in Figure 2(B), conventional FMCW LiDAR cannot detect beat signals whose beat frequency IF falls outside the reception band, resulting in a limit to the measurement distance imposed by the reception band. Furthermore, since the repetition frequency (refresh rate) is proportional to the sweep rate γ, if the sweep rate γ is limited, the refresh rate will also be limited.

[0026] In this disclosure, in order to eliminate the measurement distance limitation imposed by the receiving band, the above-mentioned optical frequency comb generator 7 is introduced into the reference light path, that is, between the coupler 2-1 and the optical 90-degree hybrid 8.

[0027] FIG. 3 shows an example of an optical frequency comb generated by the optical frequency comb generator 7. The optical frequency comb generator 7 according to this embodiment generates an optical frequency comb consisting of a plurality of different frequencies, including the frequency of the reference light input from the coupler 2-1. In the optical frequency comb shown in FIG. 3, for ease of understanding, ref 1 corresponds to the laser light whose frequency is swept by the frequency sweep light source 1, and at each time, the reference light L refHere is an example consisting of five frequencies, with two frequencies equally spaced on either side of the center 1.

[0028] The optical frequency comb according to this embodiment is merely an example, and the number of frequencies is not limited to this. Furthermore, the frequency intervals of the optical frequency comb may not be equal, but may be different. The optical duplication unit that generates an optical frequency comb containing multiple frequencies, such as those shown in FIG. 3, is not limited to the optical frequency comb generator 7, and any means capable of generating sidebands from input light may be used.

[0029] In this embodiment, the reference light input from the coupler 2-1 is linearly swept by the frequency sweep light source 1, and therefore the optical frequency comb is also linearly swept. As a result, the reference light from the coupler 2-1 in this disclosure becomes the frequency-swept optical frequency comb shown in FIG. 3 and enters the optical 90-degree hybrid 8.

[0030] 4 shows an example of the beat frequency detected by the main interferometer 20 of this embodiment. ref 1~L ref 5 and probe light L p The beat frequency IF1 is the frequency of the probe light L p and reference beam L ref The beat frequency IF2 is the beat frequency between the probe light L p and reference beam L ref The beat frequency IF3 is the beat frequency between the probe light L p and reference beam L ref The beat frequency IF4 is the beat frequency between the probe light L p and reference beam L ref The beat frequency IF5 is the beat frequency between the probe light L p and reference beam L ref The beat frequency is between 0 and 5.

[0031] As shown in Fig. 4, the probe light delayed during propagation to the DUT 5 interferes with all of the reference lights constituting the optical frequency comb, generating beat signals with beat frequencies IF1 to IF5. In the present disclosure, the receiving bands of balanced photodetectors 9-1 and 9-2, etc., detect the observed beat frequency by comparing the probe light with the reference light L of the frequency closest to the probe light. ref 2, resulting in only the beat frequency IF2.

[0032] Here, if the frequency spacing of the optical frequency comb shown in Figure 5, which has evenly spaced frequencies, is Δf, then the minimum beat frequency will be Δf / 2 or less. Therefore, it is desirable for the main interferometer 20 to have a reception band of at least Δf / 2 or less. As shown in Figure 5, narrowing the frequency spacing Δf of the optical frequency comb lowers the maximum value Δf / 2 of the minimum beat frequency, making it possible to detect the minimum beat frequency even with a main interferometer 20 that has a narrow reception band. Note that in the case of an optical frequency comb with uneven frequency spacing, the same explanation can be given as for the case of evenly spaced frequencies if the maximum frequency spacing is Δf.

[0033] 5 only shows a portion of the reference and probe beams, and assumes that the reference and probe beams are linearly swept to even higher frequency bands. If the optical frequency comb generator 7 generates an optical frequency comb with a frequency band sufficiently wider than the frequency sweep width ΔF of the frequency sweep light source 1, interference with any of the optical frequency comb components can be observed without expanding the reception bands of the balanced photodetectors 9-1 and 9-2, even when the DUT 5 is far away. Since it is not clear which frequency component is interfering, periodic ambiguity remains in the ranging results, but this can be eliminated by performing a rough measurement in advance.

[0034] In the above configuration, the optical frequency comb generator 7 may be located in the probe light path before the main interferometer 20, i.e., between the optical circulator 3 and the optical 90-degree hybrid 8. In this case, the probe light reflected by the DUT 5 is input to the optical frequency comb generator 7. As a result, as shown in FIG. 6, the optical frequency comb generator 7 generates an optical frequency comb consisting of multiple different frequencies, including the frequency of the probe light reflected by the DUT 5. Meanwhile, the reference light is a single light. In this case, the same effect as the configuration shown in FIG. 1 can be achieved by measuring the frequency of the beat signal generated by interference between the reference light and the light with the frequency closest to the frequency of the reference light in the optical frequency comb based on the probe light.

[0035] As described above, by introducing the optical frequency comb generator 7, it is possible to eliminate the limit on the measurement distance imposed by the receiving band without reducing the frequency sweep speed.

[0036] (Embodiment 2) Figure 7 shows an embodiment of the present disclosure based on the FWCW LiDAR method. Generally, the frequency sweep trace of a frequency swept light source is not perfectly linear, but has a certain level of imperfection (nonlinearity). This nonlinearity means fluctuations in the sweep rate γ, which causes fluctuations in the beat frequency from a certain distance, making it impossible to achieve the theoretical distance resolution given by Equation (2).

[0037] To solve this problem, the non-contact distance measuring device according to this embodiment further includes an auxiliary interferometer 21. The auxiliary interferometer 21 includes a coupler 2-4, a balanced photodetector 9-3, an AD converter 10-2, and a calculation unit 11. The auxiliary interferometer 21 uses light without delay and a delay time τ aux The auxiliary interferometer 21 is an interferometer for obtaining the phase of a beat signal due to interference with light delayed by a delay time τ aux This is the same as the beat signal based on the probe light reflected from the object 5 to be measured at a distance corresponding to the above.

[0038] The coupler 2-2 splits the laser light from the frequency sweep light source 1 into two, and inputs one to the coupler 2-1 as light for the main interferometer 20, and the other to the coupler 2-3 for the auxiliary interferometer 21. This allows a portion of the frequency sweep light to be extracted. The coupler 2-1 performs the same operation as in the first embodiment on the light input from the coupler 2-2.

[0039] In the auxiliary interferometer 21, the coupler 2-3 splits the light input from the coupler 2-2 into two, and inputs one of the two to the coupler 2-4 and the other to the delay device 6. The delay device 6 adds a delay time τ aux The light is input to the coupler 2-4 with a delay of 1 / 2 sigma. The coupler 2-4 combines the light input directly from the coupler 2-3 and the light input from the delay device 6 to generate a beat signal, and then splits the beat signal into two signals which are input to the balanced photodetector 9-3. The balanced photodetector 9-3 acquires the beat signal from the coupler 2-4 as an analog electrical signal and inputs it to the AD converter 10-2. The AD converter 10-2 converts the beat signal input from the coupler 9-3 into a digital signal and inputs it to the calculation unit 11.

[0040] By "resampling" the beat signal of the main interferometer 20 at the frequency of the beat signal of the auxiliary interferometer 21 using the beat signal of the auxiliary interferometer 21, the nonlinearity of the frequency sweep of the light source can be removed.

[0041] However, this method requires the delay time τ of the auxiliary interferometer. aux In other words, the phase of the laser light from the frequency swept light source 1 is only correlated within a time period specific to each frequency swept light source 1, called the coherence time, and once this time has elapsed, the phase correlation disappears. This means that the distance (delay time) to the object 5 to be measured is equal to the delay time τ aux If the difference between the beat frequencies of the auxiliary interferometer 21 and the main interferometer 20 is greater than the coherence time, the beat frequencies of the auxiliary interferometer 21 and the main interferometer 20 will no longer be correlated and will no longer function.

[0042] Therefore, as a second point of the present disclosure, the calculation unit 11 has a built-in phase noise compensation algorithm. The principle of this phase noise compensation algorithm is described in Non-Patent Document 2. The calculation unit 11 may follow the method disclosed in Non-Patent Document 2. That is, the calculation unit 11 acquires the beat signal input from the AD converter 10-2 in FIG. 7 and calculates a delay time τ aux The calculation unit 11 obtains the phase X(t) of the beat signal of the auxiliary interferometer 21 for each time period. The calculation unit 11 calculates the phase X(t) of the beat signal of the auxiliary interferometer 21 using the phase X(t) of the beat signal of the auxiliary interferometer 21, as shown in Equation (3). N Calculate (τ).

number

[0043] Here, N is a positive integer, and τ is the delay time mentioned above. τ ≒ Nτ aux The delay time τ may be longer than the coherence time of the laser beam. aux is shorter than the coherence time of the laser light, the delay time τ is aux The phase of the beat signal of the main interferometer 20 at the delay time τ can be calculated by equation (3). N If the signal of the main interferometer 20 is resampled every time (τ) increases by a certain value, the time Nτ that exceeds the coherence time of the laser light aux It is possible to measure the distance corresponding to the nearby delay time τ. As a result, the problem of the finite coherence time mentioned above can be overcome. Also, as described in Non-Patent Document 2, the phase X N (τ) also corresponds to the phase of the laser light at the delay time τ. Therefore, by using equation (3), the nonlinearity of the frequency sweep of the laser light can be corrected, and the resolution of equation (2) can also be realized. As mentioned above, the delay time τ of the auxiliary interferometer aux must be set shorter than the coherence time of the frequency sweep light source 1 used.

[0044] The present invention discloses a method for applying this phase noise compensation algorithm to distance measurement by the following procedure: First, the distance to the object 5 is calculated by the delay τ of the auxiliary interferometer. aux Generally, the coherence length of a frequency swept light source is several tens of meters, and the delay τ aux This estimation is easy because the distance is on the same order of magnitude. For example, it is sufficient to know the approximate distance in advance using a known method such as the pulse method.

[0045] Next, assuming that the delay time of the probe light reflected from the object to be measured 5 at the estimated distance L with respect to the reference light is τ, an integer M that satisfies the formula (4) is found. (Number 4) τ ≒ Mτ ref (4)

[0046] Furthermore, using equation (3), the phase X M (τ) is calculated and used to correct the nonlinearity of the frequency sweep of the laser light. This makes it possible to achieve the theoretical resolution of Equation (2) in principle.

[0047] Although the main interferometer 20 according to this embodiment is configured to perform hardware-based processing using the optical 90-degree hybrid 8, software-based processing using the Hilbert transform may also be used. Furthermore, the auxiliary interferometer 20 according to this embodiment is configured to perform software-based processing using the Hilbert transform, but hardware-based processing using the optical 90-degree hybrid 8 may also be used.

[0048] The calculation unit 11 according to this embodiment can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. [Industrial Applicability]

[0049] The non-contact distance measuring device and method according to the present disclosure can be applied to the information and communication industry. [Explanation of symbols]

[0050] 1: Frequency swept light source 2: Coupler 3: Optical circulator 4: Lens 5: Object to be measured 6: Delay 7: Optical frequency comb generator 8: Optical 90-degree hybrid 9:Balanced photodetector 10: AD converter 11: Arithmetic section 12: RF synthesizer 13: Amplifier 20: Main interferometer 21: Auxiliary interferometer

Claims

1. 1. A non-contact distance measuring device that irradiates a frequency sweep light onto an object to be measured, and measures the frequency of a beat signal generated by interference between a probe light and a reference light reflected by the object to determine a distance to the object, an optical duplication unit that receives the reference light or the probe light and duplicates the incident light into light of a plurality of different frequencies; a main interferometer that combines the reference light and the probe light and detects the minimum beat frequency obtained by combining the combined light; Equipped with the optical duplication unit is connected between the main interferometer and a coupler that branches the frequency sweep light into the reference light and the probe light, or between the main interferometer and an optical circulator that outputs the probe light reflected by the object to the main interferometer, the main interferometer multiplexes the probe light from the optical circulator with the reference light duplicated to a plurality of frequencies in the optical duplication unit, or multiplexes the reference light from the coupler with the probe light duplicated to a plurality of frequencies in the optical duplication unit; Non-contact distance measuring device.

2. a coupler that splits a part of the frequency swept light into two; One of the two portions of the frequency swept light split by the coupler is provided with a delay time τ shorter than the coherence time of the frequency swept light. ａｕｘ a delayer for generating a delay of an auxiliary interferometer for acquiring a phase X(t) of a beat signal resulting from interference between the one part delayed by the delay device and the other part of the frequency swept light branched into two by the coupler, Using the phase X(t) of the beat signal acquired by the auxiliary interferometer, an integer N, and equation (C1), the phase X of the frequency swept light at a delay time τ of the probe light relative to the reference light, which corresponds to the optical path difference between the reference light and the probe light, is calculated. Ｎ (τ) and correct the nonlinearity of the frequency swept light at the minimum beat frequency obtained by the main interferometer.

2. The non-contact distance measuring device according to claim 1. [Math C1]

3. The delay time τ is estimated in advance, and the integer N that satisfies the formula (C2) is used.

3. The non-contact distance measuring device according to claim 2. (Number C2) τ≒Nτ ａｕｘ (C2)

4. The optical duplication unit generates an optical frequency comb having a frequency range wider than the frequency sweep width of the frequency sweep light as the light of the plurality of frequencies.

4. A non-contact distance measuring device according to claim 1.

5. 1. A non-contact distance measuring method for determining a distance to an object to be measured by irradiating the object with frequency sweep light and measuring a frequency of a beat signal generated by interference between a probe light reflected by the object and a reference light, comprising: an optical duplication unit connected between a main interferometer and a coupler that splits the frequency sweep light into the reference light and the probe light duplicates the reference light into a plurality of different frequencies, or an optical duplication unit connected between the main interferometer and an optical circulator that outputs the probe light reflected by the object to the main interferometer duplicates the probe light into a plurality of frequencies; the main interferometer multiplexes the probe light from the optical circulator with the reference light duplicated to a plurality of frequencies in the optical duplication unit, or multiplexes the reference light from the coupler with the probe light duplicated to a plurality of frequencies in the optical duplication unit, and detects the minimum beat frequency obtained by the multiplexing; A non-contact distance measurement method.

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