Non-contact distance measuring device and method

Abstract

To specify which frequency of a plurality of duplicated frequencies, a frequency at which a beat signal is generated during detection of the beat signal is.SOLUTION: A non-contact type distance measuring device irradiates an object to be measured with frequency sweep light, and measures the frequency of a beat signal caused by the interference between probe light reflected on the object to be measured and reference light, to determine the distance to the object to be measured, and the non-contact type distance measuring device comprises a light duplication unit that duplicates the reference light into a plurality of rays of light with a nonuniform delay interval.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Accurate distance measurement technology is crucial for measurements such as the shape measurement of large structures. Numerous applications exist, including the measurement of shapes of artificial objects like parabolic antennas and buildings, and the measurement of 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 measurements of large structures for purposes such as health monitoring of buildings and disaster prevention.

[0003] LiDAR (Light Detection and Ranging) is a non-contact ranging technology that uses laser light to measure the optical path length to an object being measured. In this technology, frequency-modulated continuous wave (FMCW) LiDAR measures distance using a single light source and has the capability to detect velocity and vibration. In FMCW LiDAR, the frequency is swept, and the frequency difference (beat frequency, IF) caused by interference with the reflected light is converted into distance. Using a light source with a sweep bandwidth of 100 nm, a resolution of approximately 12 μm can be achieved.

[0004] However, with FMCW-type LiDAR, the measurement distance is limited to several tens of meters due to the coherence length of the light source. Furthermore, measurements cannot be taken when the obtained 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 speed 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 speed must be sacrificed. Moreover, since the measurement repetition frequency (refresh rate) is proportional to the frequency sweep speed, sacrificing the frequency sweep speed means sacrificing the refresh rate. Due to these two factors, FMCW-type LiDAR has been limited exclusively to measuring relatively short distances of several tens of meters or less. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Takahiro Nagata et al., "Frequency Modulated Continuous Wave Optical Distance Meter Using Wavelength Sweep Type Optical Frequency Comb," 2022 (73rd) Joint Conference of Electrical and Information Engineering Societies, Chugoku Branch, R22-11-04. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] A technique has been proposed to extend the measurement distance in a simple distance measuring device using a single light source without reducing the frequency sweep speed (see, for example, Non-Patent Document 1). In Non-Patent Document 1, one of the reference light or probe light is duplicated into multiple lights of different frequencies and combined with the other of the reference light or probe light. This generates beat signals of multiple frequencies, and the beat frequency that falls within the receiving band is detected.

[0007] However, in Non-Patent Document 1, multiple frequencies of light were generated, and it was not possible to identify which frequency generated the beat signal when detecting the beat signal. Therefore, the present disclosure aims to make it possible to identify which of the multiple replicated frequencies generated the beat signal when detecting the beat signal. [Means for solving the problem]

[0008] To achieve the above objective, this disclosure duplicates a reference light and interferes the duplicated reference light with a probe light. During this duplication, the incident light is duplicated into multiple lights with different delays such that the optical frequency intervals at each time (each instant) are non-uniform.

[0009] Specifically, the non-contact distance measuring device according to the present disclosure irradiates the object to be measured with frequency-swept light, and measures the distance to the object to be measured by measuring the frequency of the beat signal due to the interference between the probe light reflected by the object to be measured and the reference light, and executes the non-contact distance measuring method according to the present disclosure.

[0010] The non-contact distance measuring device according to the present disclosure includes an optical replication unit that replicates the reference light into a plurality of lights with non-uniform delay intervals, and generates a plurality of beat signals by multiplexing the plurality of lights replicated by the optical replication unit with the probe light, and obtains the distance to the object to be measured by detecting two or more frequencies among the plurality of beat signals.

[0011] The non-contact distance measuring method according to the present disclosure includes a procedure in which an optical replication unit replicates the reference light into a plurality of lights with non-uniform delay intervals, and generates a plurality of beat signals by multiplexing the plurality of lights replicated by the optical replication unit with the probe light, and obtains the distance to the object to be measured by detecting two or more frequencies among the plurality of beat signals.

[0012] The optical replication unit may adopt a mode in which a plurality of circular transmission paths with different lengths are connected in parallel. Here, one length L7 of the plurality of circular transmission paths may be different from an integer multiple of the length difference ΔL7 of the plurality of circular transmission paths. Also, the frequency of the frequency-swept light that changes with time when propagating through each circular transmission path included in the plurality of circular transmission paths may be smaller than twice the reception band of the main interferometer that detects the frequency of the beat signal. Also, optical amplifiers with different amplification factors may be inserted into the plurality of circular transmission paths.

[0013] Note that the above disclosures can be combined as much as possible.

Advantages of the Invention

[0014] According to this disclosure, when detecting a beat signal, it is possible to identify which of the multiple replicated frequencies generated the beat signal. Therefore, despite the simple configuration using a single light source, this disclosure can achieve a measurement distance of several kilometers and a resolution of several tens of micrometers without reducing the measurement speed, and furthermore, it can mitigate the periodic ambiguity of the distance measurement results. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example of the configuration of a non-contact distance measuring device related to this disclosure. [Figure 2] This diagram illustrates conventional reference and probe light, where (a) shows the frequencies of the reference and probe light, and (b) shows the interference signal spectrum. [Figure 3] This diagram illustrates the frequencies of the reference light and probe light. [Figure 4] An example of a beat frequency is shown. [Figure 5] This disclosure shows an example of the configuration of the optical replication unit. [Figure 6] This is a diagram illustrating the frequency of the reference light in this disclosure. [Figure 7] This is a diagram illustrating the frequency of the reference light in this disclosure. [Figure 8] This figure illustrates the frequencies of the reference light and test light in this disclosure. [Figure 9] An example of the beat frequency of this disclosure is shown. [Figure 10] This is a diagram illustrating the frequency of the reference light in this disclosure. [Figure 11] An example of the beat frequency of this disclosure is shown. [Figure 12] Here is an example of a workflow for calculating the distance to the object being measured. [Figure 13] This is a diagram illustrating the frequency of the reference light in this disclosure. [Figure 14] An example of the beat frequency of this disclosure is shown. [Modes for carrying out the invention]

[0016] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0017] Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 shows an embodiment of the non-contact distance measuring device of the present disclosure based on the FWCW type LiDAR system. 1 is a frequency-swept light source, 2 is a coupler for splitting or combining light, 3 is an optical circulator, 4 is a lens, 5 is the object to be measured, 6 is a delay unit, 7 is an optical replication unit, 8 is an optical 90-degree hybrid, 9 is a balanced photodetector, 10 is an AD converter, 11 is a computing unit such as a computer, and 12 is an RF synthesizer.

[0018] The optical replication unit 7 replicates the reference light into light of multiple different frequencies. The optical 90-degree hybrid 8, balanced photodetectors 9-1 and 9-2, and AD converter 10-1 constitute the main interferometer 20, which functions as the photodetector in this disclosure. Hereinafter, the "receiving band of the photodetector" will be abbreviated as "receiving band".

[0019] The frequency-swept light source 1 emits laser light whose frequency is linearly modulated. Its frequency is swept at a constant sweep speed γ [Hz / s] over a constant frequency sweep time ΔT and over a frequency sweep width ΔF. In this embodiment, the light output from the frequency-swept light source 1 is described as laser light, but it is not limited to this as long as it is coherent light.

[0020] Coupler 2-1 splits the light input from the frequency-swept light source 1 into two, inputting one as probe light to the optical circulator 3 and the other as reference light to the optical replication unit 7. The optical circulator 3 inputs the probe light from coupler 2-1 to lens 4. The optical circulator 3 also inputs the light from lens 4 to optical 90-degree hybrid 8. Lens 4 converts the probe light from the frequency-swept light source 1 into a plane wave. Lens 4 also focuses the probe light reflected from the object under test 5 and inputs it to the optical circulator 3. In this disclosure, the probe light reflected from the object under test 5 may be referred to as test light.

[0021] The optical replication unit 7 replicates the reference light into multiple lights of different frequencies. The optical replication unit 7 inputs the multiple generated reference lights into 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 uses this delay time to measure the distance. In Figure 1, the calculation unit 11 is included in the main interferometer 20, but the main interferometer 20 and the calculation unit 11 may be separate.

[0022] Specifically, the 90-degree optical hybrid 8 generates the in-phase component I of the beat signal obtained by combining the reference light and the reflected light from the object under test 5, and inputs it to the balanced photodetector 9-1. The 90-degree optical hybrid 8 also generates the orthogonal component Q of the beat signal obtained by combining the reference light, which has been phase-shifted by 90 degrees, and the reflected light from the object under test, and inputs it to the balanced photodetector 9-2.

[0023] The balanced photodetector 9-1 acquires an analog electrical signal of the common-mode component I of the beat signal based on the input from the 90-degree optical 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 90-degree optical hybrid 8 and inputs it to the AD converter 10-1. The AD converter 10-1 converts the analog electrical signal of the common-mode component I of the beat signal input from the balanced photodetector 9-1 and the analog electrical signal of the quadrature component Q of the beat signal input from the balanced photodetector 9-2 into digital signals and inputs them to the calculation unit 11.

[0024] Here, the interference between the reference light and probe light in a conventional FMCW-type LiDAR without an optical replication unit 7 will be explained using Figure 2. That is, in a conventional FMCW-type LiDAR, the reference light from coupler 2-1 is directly input to the optical 90-degree hybrid 8 in the main interferometer shown in Figure 1. In a conventional FMCW-type LiDAR, the reference light from coupler 2-1 and the probe light, which is delayed by the distance traveled to the object under test 5 relative to the reference light, arrive, and a beat signal with a frequency corresponding to the frequency difference between them is generated. Hereafter, the frequency of the beat signal will be referred to as the beat frequency IF. Since 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, distance measurement is possible.

[0025] Specifically, the beat signal is expressed in complex number form as shown in equation (1), using the I-phase and Q-phase components of the beat signal output from the optical 90-degree hybrid 8. (Math 1) I + jQ = exp(jγτt) (1)

[0026] The calculation unit 11 determines the phase of the beat signal from equation (1) based on the common-mode component I and the quadrature component Q of the hybrid signal input from the AD converter 10-1. Here, 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.

[0027] Generally, the distance resolution Δz of an FMCW-type LiDAR is expressed as follows using the frequency sweep width ΔF. (Math 2) Δz = c / (2ΔF) (2)

[0028] In other words, to improve the distance resolution Δz, it is necessary to increase the frequency sweep width ΔF. Furthermore, the beat frequency IF is proportional to the delay time τ, which varies depending on the distance to the object under measurement 5, and the sweep speed γ. Therefore, if the receiving bandwidth is constant, there will be a limit to the product of the sweep speed γ and the distance. Specifically, in conventional FMCW type LiDAR, as shown in Figure 2(B), beat signals with a beat frequency IF outside the receiving bandwidth cannot be detected, resulting in a limitation of the measurement distance due to the receiving bandwidth. Note that the repetition frequency (refresh rate) is proportional to the sweep speed γ, so if the sweep speed γ is limited, the refresh rate will also be limited.

[0029] In this disclosure, in order to eliminate the limitation of measurement distance due to the receiving bandwidth, the aforementioned optical replication unit 7 is introduced into the reference optical path, that is, between the coupler 2-1 and the optical 90-degree hybrid 8.

[0030] The non-contact distance measuring method of this embodiment includes a procedure in which the optical replication unit 7 replicates a reference light into a plurality of lights with non-uniform delay intervals, and generates a plurality of beat signals by combining the plurality of lights replicated by the optical replication unit 7 with the probe light, and determines the distance to the object to be measured 5 by detecting two or more frequencies of the plurality of beat signals.

[0031] Figure 3 shows an example of the reference light generated by the optical replication unit 7. In this embodiment, the optical replication unit 7 receives the reference light input from the coupler 2-1 at a frequency L ref Includes 1 and multiple different frequency L ref 1~L ref A light frequency comb consisting of 5 is generated. The light frequency comb according to this embodiment is just an example, and the number of frequencies is not limited thereto. Also, the frequency intervals f of the light frequency comb do not have to be equal and may be different.

[0032] In this embodiment, the reference light input from coupler 2-1 is linearly swept by the frequency-swept light source 1, and therefore the optical frequency comb is also linearly swept. As a result, the reference light from coupler 2-1 in this disclosure becomes a frequency-swept optical frequency comb as shown in Figure 3 and is incident on the optical 90-degree hybrid 8.

[0033] Figure 4 shows an example of the beat frequency detected by the main interferometer 20 of this embodiment. The reference light L that constitutes the optical frequency comb at the delay time τ ref 1~L ref 5 and probe light L p The beat frequencies IF1 to IF5 are shown below. As shown in Figure 4, the probe light, which has been delayed by propagation to the object under test 5, interferes with all of the reference light constituting the optical frequency comb, generating multiple beat signals with beat frequencies IF1 to IF5.

[0034] If the frequency spacing of the optical frequency comb shown in Figure 3, where the frequencies are equally spaced, is f, then the minimum beat frequency will be less than or equal to f / 2. Therefore, it is desirable that the main interferometer 20 have a receiving bandwidth of at least f / 2. Narrowing the frequency spacing f of the optical frequency comb lowers the maximum value f / 2 of the minimum beat frequency, so that the minimum beat frequency can be detected even with the main interferometer 20 having a narrow receiving bandwidth. Note that in the case of optical frequency combs where the frequency spacing is not equally spaced, the explanation can be the same as in the case of equally spaced frequencies if the maximum frequency spacing is taken as f.

[0035] Figure 3 only shows a portion of the reference and probe light, and it is assumed that the reference and probe light are linearly swept to even higher frequency bands. If the optical replication unit 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 even when the object under measurement 5 is far away, without extending the receiving bandwidth of balanced photodetectors 9-1 and 9-2.

[0036] Here, in the present disclosure, the plurality of beat frequencies shown in FIG. 4 depend on the frequency of the frequency-swept light generated by the optical replication unit 7. The frequency-swept light generated by the optical replication unit 7 is light obtained by shifting the original frequency-swept light in the time direction. Since a plurality of frequency-swept lights are generated in the optical replication unit 7, periodic ambiguity remains in the frequency-swept light that generates the beat frequency IF2. Therefore, in the present disclosure, the optical replication unit 7 replicates the incident light into a plurality of lights with different delays so that the optical frequency interval at each time (each instant) is non-uniform. The arithmetic unit 11 is based on the frequency difference between the beat frequencies IF2 and IF3 and the frequency difference between the beat frequencies IF3 and IF1, and the frequency of the reference light that generates the beat frequency IF2 is L ref It is determined that the frequency is that of 2.

[0037] FIG. 5 shows a configuration example of the optical replication unit 7. The optical replication unit 7 of the present embodiment includes a plurality of loop transmission lines 71A and 71B connected in parallel. The lengths of the loop transmission lines 71A and 71B are different. The length of the loop transmission line 71A is L7, and the length of the loop transmission line 71B is L7 + ΔL7. The length L7 is different from an integer multiple of ΔL7.

[0038] FIGS. 6 and 7 show an example of the relationship between the test light and the reference light. When the distance to the measurement target 5 is zero, as shown in FIG. 6, the original frequency-swept light L ref 1 output from the frequency-swept light source 1 changes in frequency according to the frequency-sweeping speed of the frequency-swept light source 1 from time t = 0. The farther the measurement target 5 is, as shown in FIG. 7, the time τ of the test light shifts to the right.

[0039] The frequency-swept light generated by the optical loop transmission line 71A is generated at intervals of a delay interval τ7 after the frequency-swept light L ref 1. The reference light L ref A1 to L ref A4 generated by the optical loop transmission line #71A# is light obtained by shifting the original frequency-swept light in the time direction by τ7 = L7 / ν with respect to the length L7 of the optical loop transmission line 71A. Here, ν g gL is the group velocity of light propagating through the optical circuit 71A. The reference light L generated in the optical circuit 71B ref B1~L ref B4 is the reference light L ref A1~L ref For A4, Δτ7 = ΔL7 / v in the time direction. g The light has shifted.

[0040] The length of the circular transmission path 71B is L7 + ΔL7. Therefore, the time interval between the frequency-swept light generated by the optical circular transmission path 71A and the frequency-swept light generated by the optical circular transmission path 71B is Δτ7, 2Δτ7, 3Δτ7, 4Δτ7, ... nΔτ7, and so on, relative to the original frequency-swept light L ref It increases as it moves away from 1.

[0041] Figure 8 shows an example of the optical frequency of the reference light at time T shown in Figure 6. Since the frequency-swept light source 1 is frequency-swept light, when the frequency-swept light generated by the optical circuit transmission line 71A has a frequency interval f, the frequency-swept light generated by the optical circuit transmission line 71B will have a frequency difference Δf corresponding to ΔL7, and its frequency interval will be f+Δf. For this reason, the frequency-swept light generated by the optical circuit transmission line 71B will increase as it moves away from the frequency f0 of the frequency-swept light source 1, such as Δf, 2Δf, 3Δf, 4Δf, ...nΔf.

[0042] Furthermore, the delay time τ7 is the group velocity ν of light propagating through the optical circuit 7. g and τ7=L7 / ν g This relationship exists. Therefore, shortening the length L7 of the optical circuit transmission path 7 lowers the maximum value τ7γ / 2 of the minimum beat frequency, making it possible to detect the minimum beat frequency even with the main interferometer 20 which has a narrow receiving bandwidth BW. For example, if the receiving bandwidth of the main interferometer 20 is BW, then the length L7 of the optical circuit transmission path 7 is 2ν g The value should be shorter than ×BW / γ. This makes it possible to detect the smallest beat frequency for any given receiving bandwidth BW.

[0043] When the frequency sweep speed of the frequency sweep light source 1 is γ (Hz / s), the delay time τ is the frequency difference f between the test light and the reference light.b It can be expressed as follows using the following: τ=f b / γ (3) The minimum beat frequency between the test light and the reference light is less than or equal to τ7γ / 2. Therefore, the main interferometer 20 is configured with a receiving bandwidth BW of at least less than or equal to τ7γ / 2.

[0044] The distance z(m) to the object to be measured can be calculated using the following formula. z = cf b / 2γ (4) However, c is the speed of light (m / s).

[0045] Figure 9 shows an example of a beat frequency to be measured. When the receiving bandwidth of the beat frequency is BW, f+Δf should be less than twice the receiving bandwidth BW. That is, the following should hold: (f+Δf) / 2 <BW (5)

[0046] Figures 10 and 11 show examples of beat frequency measurement. Figures 11(1) to (4) show the beat frequency patterns when the test light has the frequency shift amounts shown in Figures 10(1) to (4). Light with a frequency shift amount greater than frequency nf is removed by a filter. Here, n is an integer that satisfies the following equation. n <f / Δf+1 (6)

[0047] In this embodiment, one or two beat frequencies ν1 or ν2 are measured according to the beat frequency of the test light, as shown in Figures 11(1) to 11(4). For example, the measured beat frequencies are defined as ν1 and ν2 in ascending order. There are four possible relationships between the measured beat frequencies. In this embodiment, the distance z of the object to be measured is calculated based on the flow shown in Figure 12.

[0048] The system determines if there is only one beat frequency (S101), and if there is, it determines that it is pattern 1 as shown in Figure 11(1). Note that even if the device is at the very edge of the measurement range, only one beat frequency will be measured, but in this case, it can be treated as being outside the measurement range.

[0049] When two beat frequencies are measured, the frequency difference Δν between them is calculated. When Δν = f, it is determined to be pattern 2 as shown in Figure 11(2). When Δν is an integer multiple of Δf, it is determined to be pattern 4 as shown in Figure 11(4). When Δν is not an integer multiple of Δf, it is determined to be pattern 3 as shown in Figure 11(3).

[0050] When calculating the distance z (m) to the object to be measured, the frequency difference f b Set it as follows: When pattern 1 or 2 is used, the measured beat frequency ν1 is f b Set to (S111). In pattern 4, use the following equation to determine f b Set (S112). f b =(Δν / Δf)·f-ν1(7) In pattern 3, use the following equation to determine f b Set (S113). f b ={(f-Δν) / Δf+1}·f-ν²(8)

[0051] Figures 13 and 14 show specific calculation examples when f = 15 MHz, Δf = 2 MHz, and BW = 10 MHz. In this embodiment, n·f = 105, and light with a frequency shift amount greater than this is removed by a filter. When the frequency shift amount of the test light is at position (1) shown in Figure 13, it corresponds to pattern 1, so step S111 is performed, f b Set it. When the frequency shift amount of the test light is at position (2) shown in Figure 13, Δν = 4 = 2Δf, which corresponds to pattern 4. Therefore, step S112 is performed, f b Set =30-ν1 When the frequency shift amount of the test light is at position (3) shown in Figure 13, Δν = 7, which corresponds to pattern 3, so step S113 is performed, f b Set =75-ν2

[0052] The limit at which two beat frequencies can be seen is 10² + 10 = 112 MHz. At this point, the maximum distance that can be measured is: c / 2γ×112×10 6 = 56c / γ × 10 6 (m) (9) Therefore, if ΔT = 2 ms and ΔF = 5 GHz, the resolution will be 3 cm and the measurement distance will be 6720 m.

[0053] As described above, the introduction of the optical replication unit 7 eliminates the limitation of measurement distance due to the receiving bandwidth without reducing the frequency sweep speed. Furthermore, by amplifying the light using optical amplifiers 74A and 74B with different amplification factors so that the light and intensity are non-uniform with respect to frequency, the periodic ambiguity of the distance measurement results can be mitigated.

[0054] Furthermore, although the main interferometer 20 in this embodiment is configured to process using a 90-degree optical hybrid 8 in hardware, it may also be processed in software.

[0055] The arithmetic unit 11 according to this embodiment can also be implemented by a computer and a program, and the program can be recorded on a recording medium or provided via a network. [Industrial applicability]

[0056] The non-contact distance measuring device and method described herein can be applied to the information and communication industry. [Explanation of Symbols]

[0057] 1: Frequency-swept light source 2: Coupler 3: Light Circulator 4: Lens 5: Object to be measured 6: Delay device 7: Optical replication department 8: 90-degree hybrid light 9: Balanced Photo Detector 10: AD Converter 11: Arithmetic section 12, 12A, 12B: RF Synthesizer 13, 13A, 13B: Amplifier 20: Main interferometer 71A, 71B: Loop transmission line 72A, 72B, 73A, 73B: Coupler 74A, 74B: Amplifier

Claims

1. In a non-contact distance measuring device that determines the distance to an object by irradiating the object with frequency-swept light and measuring the frequency of the beat signal resulting from the interference between the probe light reflected by the object and the reference light, The device comprises a light generation unit that generates multiple lights with non-uniform delay intervals by combining the reference light after it has passed through the multiple circular transmission lines of different lengths, with multiple circular transmission lines of different lengths connected in parallel. Optical amplifiers with different amplification factors are inserted into the aforementioned plurality of circulating transmission paths. By combining the multiple lights generated in the light generation unit with the probe light, multiple beat signals are generated. The distance to the object to be measured is determined by detecting two or more frequencies among the plurality of beat signals. A non-contact distance measuring device characterized by the following features.

2. The length of one of the aforementioned multiple circular transmission paths is different from an integer multiple of the difference in the lengths of the aforementioned multiple circular transmission paths. The non-contact distance measuring device according to feature 1.

3. The frequency of the frequency-swept light, which changes over time as it propagates through each of the multiple circular transmission paths, is less than twice the receiving bandwidth of the main interferometer that detects the frequency of the beat signal. The non-contact distance measuring device according to feature 1.

4. In a non-contact distance measurement method that determines the distance to an object by irradiating the object with frequency-swept light and measuring the frequency of the beat signal resulting from the interference between the probe light reflected by the object and the reference light, The optical generation unit comprises a procedure for generating multiple optical beams with non-uniform delay intervals by combining the reference light after it has passed through the multiple optical transmission lines, in which multiple circular transmission lines, each containing optical amplifiers of different lengths and amplification factors, are connected in parallel. By combining the multiple lights generated in the light generation unit with the probe light, multiple beat signals are generated. The distance to the object to be measured is determined by detecting two or more frequencies among the plurality of beat signals. Non-contact ranging method.

Images