Distance measurement method, distance measurement device, and distance measurement system

Abstract

To provide a distance measurement device and a distance measurement method capable of reducing a distance error caused by polarization.SOLUTION: A distance measurement method includes steps of branching light generated at a laser light source into a reference optical system and a measurement optical system, detecting a reference light path measurement beat signal from reference light passing the reference optical system, detecting a measurement light path measurement beat signal from measurement light obtained via a measuring target in the measurement optical system, and measuring a distance to the measuring target on the basis of the measurement light path measurement beat signal and the reference light path measurement beat signal. The method is characterized in that a polarization-induced distance error reduction element is installed in the one or both of the reference optical system and the measurement optical system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a distance measurement method, a distance measurement device, and a distance measurement system that measure the distance to an object in a non-contact manner using light. [Background technology]

[0002] Regarding a method for measuring the distance to an object non-contact using light, Patent Document 1 describes how to improve robustness against changes in the ambient temperature by placing a reference fiber interferometer in an insulated storage box, monitoring the internal temperature, and calculating the accurate distance by correcting for changes in the optical path length due to heat in the reference fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6835919 Summary of the Invention [Problem to be solved by the invention]

[0004] According to methods such as those described in Patent Document 1 that use light to measure the distance to an object non-contact, there is a problem in that when the ambient temperature changes and the temperature of the optical fiber that makes up the distance measurement unit changes, the polarization state of the light passing through the optical fiber changes, causing a distance error in the optical interference signal.

[0005] Therefore, an object of the present invention is to provide a distance measurement method, a distance measurement device, and a distance measurement system that can reduce distance errors caused by polarization. [Means for solving the problem]

[0006] In view of the above, the present invention is a distance measurement method that splits light generated by a laser light source into a reference optical system and a measurement optical system, detects a reference optical path measurement beat signal from the reference light that has passed through the reference optical system, detects a measurement optical path measurement beat signal from the measurement light obtained in the measurement optical system via the object to be measured, and measures the distance to the object to be measured based on the measurement optical path measurement beat signal and the reference optical path measurement beat signal, characterized in that an element for reducing polarization-induced distance errors is installed in either or both of the reference optical system and the measurement optical system.

[0007] Furthermore, the present invention is defined as "a distance measurement device having an optical branching unit that branches light generated by a laser light source, a reference optical system that guides one of the branched light beams to obtain reference light that serves as a reference for distance, a measurement optical system that guides the other branched light beam and obtains reflected light from an object to be measured as measurement light, a first light receiving unit that receives the reference light that has passed through the reference optical system and detects a reference light path measurement beat signal, and a second light receiving unit that receives the measurement light reflected by the object to be measured in the measurement optical system and detects the measurement light path measurement beat signal, and which measures the distance to the object to be measured based on the measurement light path measurement beat signal and the reference light path measurement beat signal, wherein an element for reducing polarization-induced distance errors is installed in either or both of the reference optical system and the measurement optical system."

[0008] Furthermore, the present invention is defined as "a distance measurement system having an optical branching unit that branches light generated by a laser light source, a reference optical system that guides one of the branched light beams to obtain reference light that serves as a reference for distance, a measurement optical system that guides the other branched light beam to obtain reflected light from an object to be measured as measurement light, a first light-receiving unit that receives the reference light that has passed through the reference optical system and detects a reference light path measurement beat signal, and a second light-receiving unit that receives the measurement light reflected by the object to be measured in the measurement optical system and detects the measurement light path measurement beat signal, and which measures the distance to the object to be measured based on the measurement light path measurement beat signal and the reference light path measurement beat signal, wherein an element for reducing polarization-induced distance errors is installed in either or both of the reference optical system and the measurement optical system, and wherein the measurement optical system is provided with a scanning mechanism that scans the irradiation light one-dimensionally, two-dimensionally, or three-dimensionally when irradiating the object to be measured with the irradiation light." [Effects of the Invention]

[0009] According to the present invention, even when the ambient temperature of the distance measurement unit changes, it is possible to suppress distance errors caused by polarization, making it possible to accurately measure the distance to the object. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing an example of the configuration of a distance measurement device 100 according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing the principle of the FMCW method of the first embodiment. [Figure 3a] FIG. 10 is a diagram showing an interference beat signal obtained by a photodetector. [Figure 3b] FIG. 10 is a diagram showing the results obtained by performing FFT on an interference beat signal. [Figure 4a] FIG. 10 is a diagram showing an interference beat signal obtained by a photodetector. [Figure 4b] FIG. 10 is a diagram showing the results of FFT of a beat signal. [Figure 4c] FIG. 10 is a diagram showing distance errors that occur when heat is applied to an optical fiber. [Figure 5]FIG. 10 is a diagram showing an example of the configuration of a distance measurement device 100 according to a second embodiment of the present invention. [Figure 6a] FIG. 10 is a diagram showing an interference beat signal obtained by a photodetector. [Figure 6b] FIG. 10 is a diagram showing the results of FFT of a beat signal. [Figure 6c] FIG. 10 is a diagram showing distance errors that occur when heat is applied to an optical fiber. [Figure 7] FIG. 10 is a diagram showing an example of the configuration of a distance measurement device 100 according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing an example of the configuration of a distance measurement device 100 according to a fourth embodiment of the present invention. [Figure 9a] FIG. 10 is a diagram showing the results obtained by performing FFT on an interference beat signal obtained by a photoreceiver. [Figure 9b] FIG. 10 is a diagram showing distance errors that occur when heat is applied to an optical fiber. [Figure 10] FIG. 10 is a diagram showing an example of the configuration of a distance measurement device 100 according to a fifth embodiment of the present invention. [Figure 11] FIG. 10 is a diagram showing an example of the configuration of a distance measurement device 100 according to a sixth embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing an example of the configuration of a distance measurement device 100 according to a seventh embodiment of the present invention. [Figure 13] FIG. 13 is a diagram showing an example of a configuration in which a polarizer is inserted into the reference optical system of Example 7. [Figure 14] FIG. 13 is a diagram showing an example of a configuration in which an interferometer of a reference optical system in a seventh embodiment is covered with a heat insulating box and has a temperature sensor. [Figure 15a] FIG. 13 is a diagram showing an example of the configuration of a distance measurement system according to an eighth embodiment of the present invention. [Figure 15b] FIG. 13 is a diagram showing another example of the configuration of a distance measurement system according to the eighth embodiment of the present invention. [Figure 16] FIG. 13 is a diagram showing an example of the configuration of a distance measurement system according to a ninth embodiment of the present invention. [Figure 17] FIG. 19 is a diagram showing an example of the configuration of a distance measurement system according to a tenth embodiment of the present invention. [Figure 18] FIG. 16 is a diagram showing an example of the configuration of a distance measurement system according to an eleventh embodiment of the present invention. [Figure 19]13A and 13B are diagrams showing the principle of switching the irradiation direction by polarized light in the eleventh embodiment. [Figure 20] FIG. 23 is a diagram showing an example of the configuration of a distance measurement system according to a twelfth embodiment of the present invention. [Figure 21] FIG. 23 is a diagram showing an example of the configuration of a distance measurement system according to a twelfth embodiment. [Figure 22] FIG. 19 is a diagram showing a different example of the configuration of the distance measurement system of FIG. 18. [Figure 23] FIG. 23 is a diagram showing an FFT result of a detected beat signal obtained by the configuration of FIG. 22. [Figure 24] FIG. 10 is a flowchart showing a process flow for origin correction. [Figure 25] FIG. 4 is a diagram showing another form of the polarizer of the first embodiment. [Figure 26] FIG. 4 is a diagram showing another form of the polarizer of the first embodiment. [Figure 27] FIG. 10 is a diagram showing another form of the polarizing beam splitter / combiner of the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments are merely examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can also be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0012] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0013] When there are multiple components with the same or similar functions, they may be described using the same reference numeral with different subscripts. When there is no need to distinguish between these multiple components, the subscripts may be omitted.

[0014] In the embodiments, processing performed by executing a program may be described. Here, a computer executes the program using a processor (e.g., a CPU or a GPU) and performs processing defined by the program using storage resources (e.g., a memory) and interface devices (e.g., a communication port). Therefore, the entity performing the processing by executing the program may be the processor. Similarly, the entity performing the processing by executing the program may be a controller, device, system, computer, or node having a processor. The entity performing the processing by executing the program may be any computing unit, and may include a dedicated circuit that performs specific processing. Here, the dedicated circuit may be, for example, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or a CPLD (Complex Programmable Logic Device).

[0015] A program may be installed on a computer from a program source. The program source may be, for example, a program distribution server or a computer-readable storage medium. When the program source is a program distribution server, the program distribution server may include a processor and a storage resource for storing the program to be distributed, and the processor of the program distribution server may distribute the program to be distributed to other computers. In addition, in an embodiment, two or more programs may be realized as one program, or one program may be realized as two or more programs.

[0016] The present invention described below provides a polarization-induced distance error reduction element in the optical path to reduce distance errors caused by polarization. There are two methods for implementing the polarization-induced distance error reduction element: one using an orthogonal polarization component attenuating element, and the other using an inter-polarization component optical path difference generating element. The former will be described in Examples 1 to 3 using Figures 1 to 7, and the latter will be described in Examples 4 to 8 using Figures 8 to 15. Furthermore, configuration examples for a shape measurement system will be described in Examples 9 to 13 using Figures 16 to 24. [Example]

[0017] In Examples 1 to 3, a method using an orthogonal polarization component attenuation element will be described. First, Fig. 1 shows an example of the configuration of a distance measurement device 100 according to Example 1 of the present invention. The distance measurement method using the optical path difference here is based on the FMCW (Frequency Modulated Continuous Wave) method.

[0018] In the FMCW distance measurement device 100, first, a sweep waveform signal is sent from the distance measurement control unit 115 to the oscillator 102. The oscillator 102 injects a triangular wave current into the laser light source 101 to modulate the drive current. As a result, the laser light source 101 generates FM (Frequency Modulated) light whose frequency is swept over time at a constant modulation speed. Note that the laser light source 101 may be configured as a semiconductor laser device with an external resonator, and the resonant wavelength of the laser light source 101 may be changed by a triangular wave control signal from the oscillator 102. As a result, the laser light source 101 generates FM light whose frequency is swept over time.

[0019] Next, the generated FM light is split into light L1 and light L2 by optical fiber coupler 103. Note that optical fiber couplers 103, 104, 106, 109, and 110 may be beam splitters. One of the split lights, L2, is guided to the reference optical system and further split into light L21 and L22 by optical fiber coupler 104. After a constant optical path difference is provided by optical fiber 105, the split lights L21 and L22 are combined by optical fiber coupler 106 and received by optical receiver 107 as light L3. This is configured as a Mach-Zehnder interferometer, and a constant beat signal L3 proportional to the optical path difference is generated in optical receiver 107.

[0020] The other light L1 split by the optical fiber coupler 103 has a specific polarization component passing through it by a polarizer 108 (an element that attenuates orthogonal polarization components), and is split into L11 and L12 by the optical fiber coupler 109. One light L11 becomes the reference light and is guided to the optical fiber coupler 110, while the other light L12 passes through the circulator 111, is emitted into space from the fiber focuser 112, and is irradiated onto the object to be measured 114.

[0021] The light L12A reflected by the object 114 passes through the fiber focuser 112 again, passes through another port of the circulator 111, and passes through the optical fiber coupler 110, and the beat signal L4 generated by the interference between the reference light L11 and the measurement light L12A is detected by the photodetector 113.

[0022] The distance measurement control unit 115 uses the reference beat signal L3 received by the photoreceiver 107 as a sampling clock to perform A / D conversion on the measurement beat signal L4 received by the photoreceiver 113. Alternatively, the distance measurement control unit 115 samples the reference beat signal L3 and the measurement beat signal L4 at a constant sampling clock. More specifically, a signal with a phase shift of 90 degrees can be created from the reference beat signal L3 by performing a Hilbert transform. Since the local phase of the signal can be determined from the reference signal before and after the Hilbert transform, the timing at which the reference signal becomes a constant phase can be determined by interpolating this phase.

[0023] By interpolating and sampling the measurement beat signal L4 in accordance with this timing, it becomes possible to resample the measurement signal L4 using the reference signal L3 as a reference. Alternatively, the same effect can be achieved by sampling the measurement signal L4 using the reference beat signal L3 as a sampling clock in an AD / DA converter included in the distance measurement control unit 115 and performing A / D conversion. Details of the method for calculating the distance from the beat signal will be explained using Figures 2 and 3, but the distance measurement data analyzed by the distance measurement control unit 115 is sent to the control PC 116 and displayed on the display unit 117.

[0024] The analysis of the beat signal will be explained using Figure 2, which shows the principle of the FMCW method. In Figure 2, the horizontal axis is time and the vertical axis is optical frequency. There is a difference Δt in the time it takes for the reference light 201 (L11) split by the optical fiber coupler 109 in Figure 1 and received as reference light, and the measurement light 202 (L12A) reflected by the object 114 and received, to reach the optical receiver 113. However, since the frequency of the light source changes during this time, there is a beat frequency f equal to the resulting frequency difference. b A beat signal of this magnitude is detected. If the frequency sweep width is Δν and the time required to modulate by Δν is T, then the relationship shown in equation (1) holds. Furthermore, since the distance L to the measurement target is half the distance light travels during Δt, it can be calculated using the speed of light in the atmosphere, c, as shown in equation (2).

[0025]

number

[0026]

number

[0027] The distance L and the beat frequency are linearly related. Therefore, by performing an FFT (First Fourier Transform) on the measurement signal L4 obtained by the photoreceiver 113 to determine the peak position and magnitude, the reflection position and amount of reflected light from the target can be determined. Figures 3a and 3b show an example of a detected beat signal and a reflection intensity profile obtained by performing an FFT on that signal. Figure 3a shows the interference beat signal obtained by the photoreceiver. The frequency of the interference beat signal is proportional to the distance to the target. Figure 3b shows the results obtained by performing an FFT on the interference beat signal. If the horizontal axis of this figure represents the FFT frequency axis and the vertical axis represents the reflection intensity, the data near the peak will be discrete, as shown in this figure. Here, the peak width w is calculated with the distance resolution cT / 2Δν. Therefore, as shown in the figure, by fitting a function such as a quadratic or Gaussian function to three or more points near the peak point 301 and using the peak of the fitted function, it is possible to determine the position of the measurement target with an accuracy greater than the distance resolution. Although FFT has been given as an example of beat frequency analysis, the peak position may be detected with higher resolution than FFT by using, for example, the maximum entropy method.

[0028] Figures 3a and 3b show ideal results obtained when distance is measured using only a specific polarization component. In reality, leakage light occurs in optical fibers, whose polarization direction is perpendicular to that of the specific polarization component. This leakage light occurs, for example, because the optical elements in the optical fiber have a low extinction ratio. Alternatively, when optical fiber connectors are used, leakage light occurs when the extinction ratio drops due to the poor fit between the connectors.

[0029] Figures 4a, 4b, and 4c show the waveforms of detected beat signals obtained when leakage light occurs. Figure 4a shows the interference beat signal obtained by the photodetector. 401 indicates the beat signal obtained by the polarization component that is intended to be measured. 402 indicates the beat signal obtained by the leakage light component that is orthogonal to it. The amplitude ratio of beat signals 401 and 402 is approximately the same as the extinction ratio. Furthermore, if the polarization component that is intended to be measured passes through the slow axis of the optical fiber and the leakage light component that is orthogonal to it passes through the fast axis of the optical fiber, the beat signals 401 and 402 will have a distance difference corresponding to the distances they pass through the slow and fast axes of the optical fiber. For example, in Figure 1, assume that the interference origin of the FMCW method exists between the fiber focuser 112 and the object of measurement 114. Here, the interference origin refers to the position where the distance difference between the reference light 201 and the measurement light 202 shown in Figure 2 is equal. For example, assume that the distance from the optical fiber focuser to the interference origin is 200 mm. In this case, the optical fiber length of the reference light path to be equal to that length is 200 mm × 2 (round trip light path) ÷ 1.5 (optical fiber refractive index) = 300 mm. If the wavelength of the measurement light is 1.55 μm and the beat length of the optical fiber (the distance by which the wavelength of light passing through the fast axis and the slow axis differs by one period) is 5 mm, the optical path difference between the light passing through the fast axis and the slow axis will be 300 mm ÷ 5 mm × 1.55 μm = 93 μm.

[0030] Figure 4b shows the results of FFTing the beat signal shown in Figure 4a. 403 indicates the peak intensity obtained by FFTing the beat signal component 401 (which passes through the slow axis of the optical fiber), and 404 indicates the peak intensity obtained by FFTing the beat signal component 402 (which passes through the fast axis of the optical fiber). 405 indicates the component obtained by combining 403 and 404. When heat is applied to the optical fiber, stress acts on the optical fiber, changing the phase of the fast axis component relative to the slow axis, and therefore the phase of 404 relative to 403. If the peak width (w shown in Figure 3b), determined by the optical frequency sweep width, is wider than 93 μm (the optical path difference between the slow axis and fast axis of the optical fiber), the bases of 403 and 404 will overlap, causing a change in the peak detection position of combined component 405. This results in a distance error.

[0031] Figure 4c shows the distance error that occurs when heat is applied to the optical fiber. The horizontal axis shows the true distance, and the vertical axis shows the measured distance. 406 is the measured distance obtained in an ideal case where there is no light leakage into the fast axis. Here, when a temperature change is applied to the fiber, a distance offset fluctuation occurs. The amount of offset fluctuation differs depending on the phase state of the fast axis relative to the slow axis, but for example, at a certain phase, the measured distance is larger than the true distance, as shown in 407, and at another phase, the measured distance is smaller than the true distance, as shown in 408.

[0032] Therefore, in the first embodiment of the present invention, as shown in Fig. 1, a polarizer 108 (an orthogonal polarization component attenuation element) is inserted into the optical path on the light L1 side, allowing only a specific linear polarization component, for example, the slow axis, to pass and reducing leakage light of the fast axis, thereby making it possible to reduce measurement errors due to the temperature of the optical fiber. Note that, although the polarizer 108 is inserted between the coupler 103 and the coupler 109 in Fig. 1, it may be inserted after the coupler 109 or after the circulator 111. It may also be inserted between the coupler 109 and the coupler 110, between the circulator 111 and the coupler 110, or between the coupler 110 and the photoreceiver 113.

[0033] Note that when connectors are used to connect optical fiber elements, the extinction ratio may decrease depending on the fit, so fusion splicing is desirable for connecting the optical fiber elements. Also, instead of inserting a polarizer, couplers 103 and 109 with high extinction ratios may be used. In this case, fusion splicing is also desirable between the laser 101 and the coupler 103. However, lasers are consumable parts and require periodic replacement. For periodic replacement, connector connection is desirable. In this case, polarizer 108 is installed before the coupler 103, and the coupler 103 and polarizer 108 are fused together. By doing so, even if the extinction ratio decreases when a connector is used between the laser and the polarizer, the polarizer can attenuate the leakage light component, making it possible to maintain a high extinction ratio. Also, couplers 103 and 109 that block the fast axis may be used.

[0034] As described above, Figure 1 shows an example configuration of distance measurement device 100, but the idea behind the device configuration of Example 1 is, in short, to adopt "a distance measurement method in which light generated by laser light source 101 is split into a reference optical system and a measurement optical system, a reference optical path measurement beat signal is detected from reference light L3 that has passed through the reference optical system, a measurement optical path measurement beat signal is detected from measurement light L4 obtained in the measurement optical system via measurement object 114, and the distance to the measurement object is measured based on the measurement optical path measurement beat signal and the reference optical path measurement beat signal, characterized in that a polarization-induced distance error reduction element (108 or 801 and 802) that reduces distance errors caused by polarization is installed in either or both of the reference optical system and the measurement optical system," and Figure 1 exemplifies a specific implementation technique showing this processing method. Note that the following examples will mainly be described in terms of the device configuration, but a technique using this configuration can be directly substituted for a technique using this method. [Example]

[0035] In the second embodiment, a technique using an element that attenuates orthogonal polarization components will be described. Fig. 5 shows an example of the configuration of a distance measurement device 100 according to the second embodiment of the present invention. In Fig. 1, a polarizer (element that attenuates orthogonal polarization components) is inserted in the measurement optical system (light L1 side) to suppress measurement errors caused by polarization, but similar measurement errors caused by polarization can also occur in the reference optical system (light L2 side). Therefore, in Fig. 5, a polarizer 108 (element that attenuates orthogonal polarization components) is inserted before the optical fiber coupler 104, thereby allowing only a specific polarization component to pass.

[0036] Figures 6a, 6b, and 6c show the detected beat signal waveforms obtained when leakage light occurs. Figure 6a shows the interference beat signal obtained by the photodetector. 601 indicates the beat signal obtained by the polarization component that is originally desired to be measured. 602 indicates the beat signal obtained by the leakage light component of polarization orthogonal to that. The amplitude ratio of the beat signals 601 and 602 is approximately the same as the extinction ratio. Furthermore, if the polarization component that is originally desired to be measured passes through the slow axis of the optical fiber and the leakage light component orthogonal to that passes through the fast axis of the optical fiber, the beat signals 601 and 602 will have a difference in distance due to passing through the slow axis and fast axis of the optical fiber, respectively. For example, suppose the length of fiber 106 in Figure 5 is 300 mm. Here, if the wavelength of the measurement light is 1.55 μm and the beat length of the optical fiber (the distance by which the wavelength of light passing through the fast axis and the slow axis differs by one period) is 5 mm, the optical path difference between the light passing through the fast axis and the slow axis will be 300 mm ÷ 5 mm × 1.55 μm = 93 μm.

[0037] Figure 6b shows the results of FFT of the beat signal shown in Figure 6a. 603 indicates the peak intensity obtained by FFT of the beat signal component 601 (passing through the slow axis of the optical fiber), and 604 indicates the peak intensity obtained by FFT of the beat signal component 602 (transmitting through the fast axis of the optical fiber). 605 indicates the component obtained by combining 603 and 604. When heat is applied to the optical fiber, stress acts on the optical fiber, changing the phase of the fast axis component relative to the slow axis, and therefore the phase of 604 relative to 603. If the peak width (w shown in Figure 3b), determined by the optical frequency sweep width, is wider than 93 μm (the optical path difference between the slow axis and fast axis of the optical fiber), the bases of 603 and 604 will overlap, causing a change in the peak detection position of the combined component 605. This causes a distance error.

[0038] Figure 6c shows the distance error that occurs when heat is applied to the optical fiber. The horizontal axis represents the true distance, and the vertical axis represents the measured distance. The measured distance obtained in an ideal case where there is no light leakage into the fast axis is designated as 606. If temperature changes occur in the fiber, the reference beat signal 601 is affected by 602, causing the resampling timing to shift, resulting in distance gain fluctuations. The amount of gain fluctuation varies depending on the phase state of the fast axis relative to the slow axis. For example, at a certain phase, the gain increases as shown in 607, and at a certain phase, the gain decreases as shown in 608. It is also important to note that when light leakage occurs in the measurement optical system, a distance offset error occurs as shown in Figures 4a, 4b, and 4c. However, when light leakage occurs in the reference optical system, a distance gain error occurs as shown in Figures 6a, 6b, and 6c, resulting in different error patterns.

[0039] In order to suppress gain fluctuations over distance, a polarizer 108 is inserted as shown in Figure 5, which transmits only the slow axis and reduces leakage light from the fast axis, thereby making it possible to reduce measurement errors due to the temperature of the optical fiber.

[0040] If a connector is used to connect optical fiber elements, the extinction ratio may decrease depending on the fit, so fusion splicing is preferable. Also, instead of inserting a polarizer, couplers 103 and 109 with high extinction ratios may be used. In this case, fusion splicing is also preferable between laser 101 and coupler 103. However, lasers are consumable parts and require periodic replacement. For periodic replacement, connector connection is preferable. In this case, polarizer 108 is installed before coupler 103, and coupler 103 and polarizer 108 are fused together. By doing so, even if the extinction ratio decreases when a connector is used between the laser and polarizer, the polarizer can cut leakage light, making it possible to maintain a high extinction ratio. Couplers 103 and 105 may be of a type that blocks the fast axis. [Example]

[0041] In the third embodiment, a method using an element for attenuating orthogonal polarization components will be described. FIG. 7 shows an example of the configuration of a distance measurement device 100 according to the third embodiment of the present invention. FIG. 7 shows a configuration in which polarizers are inserted in both the measurement optical system (light L1 side) and the reference optical system (light L2 side). As described in the first embodiment, by inserting the polarizer 108B in the measurement optical system (light L1 side), it is possible to suppress the offset fluctuation in distance caused by polarization. The polarizer may be inserted after the coupler 109 or after the circulator 111. It may also be inserted between the coupler 109 and the coupler 110, between the circulator 111 and the coupler 110, or between the coupler 110 and the photoreceiver 113.

[0042] Furthermore, as described in the second embodiment, by inserting polarizer 108A into the reference optical system (light L2 side), it is possible to suppress distance gain fluctuations caused by polarization. Polarizer 108A may be inserted before coupler 103. In that case, polarizer 108B may be omitted because it produces the same effect as polarizer 108B inserted into the measurement optical system. However, this is premised on the fact that coupler 103 maintains an extinction ratio equivalent to that of the polarizer. Furthermore, fusion is desirable between optical fiber elements to maintain a high extinction ratio. [Example]

[0043] In the fourth and subsequent embodiments, a method using an element for generating an optical path difference between polarization components will be described. Fig. 8 shows an example of the configuration of a distance measurement device 100 according to a fourth embodiment of the present invention. In the first to third embodiments, an orthogonal polarization component attenuation element (polarizer 108) is inserted into the measurement optical system or the reference optical system as an element for reducing polarization-induced distance errors, thereby allowing only specific polarization components to pass.

[0044] In contrast to this, the following describes a method of using an inter-polarization component optical path difference generating element as a method of realizing an element for reducing polarization-induced distance errors. However, since the configuration of the measurement optical system or reference optical system in the distance measurement device 100 of Example 4 in Figure 8 is basically the same as that in Figure 1, a description thereof will be omitted here. The only difference is that a configuration is adopted in which a distance difference is provided between the slow axis and fast axis components of the optical fiber to reduce measurement errors caused by polarization, and the following description will focus mainly on this point.

[0045] 8, a polarized beam splitter 801 is provided after the circulator 111 to separate the light L12 into two components (slow axis and fast axis) with orthogonal polarization. After an optical path difference is established by changing the length of the optical fiber between the two split components, the light is combined again by a polarized beam combiner 802. The combined light is guided to the optical fiber focuser 112 and irradiated onto the target.

[0046] In Fig. 8, the polarized beam splitter 801 and polarized beam combiner 802 are inserted after the circulator 111, but they may also be inserted before the circulator 111. Furthermore, they may also be inserted between the optical fiber couplers 109 and 110, or between the circulator 111 and the optical fiber coupler 110. In short, Fig. 8 shows an arrangement in which elements for generating an optical path difference between polarization components (polarized beam splitter 801 and polarized beam combiner 802) are installed on the measurement optical system side as a method for realizing an element for reducing polarization-induced distance errors. In addition, it is desirable to fusion-splice the optical fiber elements to maintain a high extinction ratio.

[0047] Figure 9a shows the result of FFT of the beat signal obtained by the photodetector 113. 901 indicates the peak intensity of the FFT spectrum obtained by the beat component transmitted through the slow axis, and 902 indicates the peak intensity of the FFT spectrum obtained by the beat component transmitted through the fast axis. Because an optical path difference is created by the polarized beam splitter 801 and polarized beam combiner 802, the peak positions can be separated by more than the peak width (w in Figure 3b) determined by the optical frequency sweep width. In this case, even if the phase of the leaked light fluctuates and the phase of the peak intensity of 902 changes, it does not affect the peak intensity of 901, so no distance error occurs.

[0048] The resulting distance error is shown in Figure 9b. The horizontal axis represents the true distance, and the vertical axis represents the measured distance. The measured distance obtained when there is no light leakage onto the fast axis is designated as 903. In Figures 4a, 4b, and 4c, an offset error occurs when the phase of the leakage light changes, but in Figures 9a and 9b, no distance offset error occurs even if the phase of the leakage light changes. [Example]

[0049] FIG. 10 shows an example of the configuration of a distance measurement device 100 according to a fifth embodiment of the present invention. In the fourth embodiment, a polarizing beam splitter 801 and a polarizing beam combiner 802 were inserted into the measurement optical system to create a distance difference between orthogonal polarization components. In the fifth embodiment, a similar method is used in the reference optical system. The optical fiber coupler 103 splits the light into light L1 and light L2, and the light L1 guided to the reference optical system is separated by the polarizing beam splitter 801 into two components (slow axis and fast axis) with orthogonal polarization. After creating an optical path difference between the two components, the light is combined again by the polarizing beam combiner 802 and guided to the optical coupler 104. Here, by making the distance difference between the polarizations equal to or greater than the peak width (w in FIG. 3b) determined by the optical frequency sweep width, it is possible to suppress gain fluctuations caused by polarization. [Example]

[0050] Fig. 11 shows an example of the configuration of a distance measurement device 100 according to a sixth embodiment of the present invention. Fig. 11 shows a configuration in which a polarizing beam splitter and a polarizing beam combiner are inserted in both the measurement optical system and the reference optical system.

[0051] As described in Example 4, offset fluctuations in distance caused by polarization can be suppressed by inserting a polarizing beam splitter 801B and a polarizing beam combiner 802B into the measurement optical system. Furthermore, gain fluctuations in distance caused by polarization can be suppressed by inserting a polarizing beam splitter 801A and a polarizing beam combiner 802A into the reference optical system as described in Example 5. [Example]

[0052] FIG. 12 shows an example of the configuration of a distance measurement device 100 according to a seventh embodiment of the present invention. In this configuration, a polarization switch 1201 and a polarization beam splitter 1202 are added to the configuration of FIG. 8 of the fourth embodiment in order to switch the measurement direction. The polarization switch 1201 can switch the polarization of the transmitted light of the light emitted from the laser 101. The light that passes through the fiber coupler 109, the circulator 111, the polarization beam splitter 801, and the polarization beam combiner 802 is irradiated into space from the fiber focuser 112. The irradiation direction of the light irradiated to the polarization beam splitter 1202 can be switched depending on its polarization state. For example, light that vibrates parallel to the incident plane of the polarization beam splitter 1202 is transmitted and therefore irradiates the measurement object 114, while light that vibrates perpendicular to the incident plane is reflected and therefore irradiates the measurement object 1141.

[0053] In this case, by using a polarized beam splitter 801 and a polarized beam combiner 802, it is possible to transmit both polarized components, making it possible to switch the measurement direction using a polarization switcher.

[0054] In contrast, when the polarizer 108 described in Fig. 1 of the first embodiment is used, only light polarized in one direction passes through, and therefore the measurement direction cannot be switched. The use of the polarizing beam splitter 801 and the polarizing beam combiner 802 has the advantage of being able to pass both polarized lights while suppressing the offset in distance caused by polarization.

[0055] Figure 13 shows a configuration in which a polarizer 108 is inserted into the reference optical system to suppress distance gain fluctuations caused by polarization, as opposed to Figure 12. Because the reference optical system does not perform polarization switching, it is sufficient to insert a polarizer 108 and allow only one polarized light to pass through. However, a configuration using the polarizing beam splitter 1001 and polarizing beam combiner 1002 described in Figure 10 may also be used.

[0056] 13, Fig. 14 has a configuration in which the reference fiber interferometer portion (optical couplers 104, 106, optical fiber 105) that serves as the distance standard is covered with a heat insulating box 1401, the temperature inside the heat insulating box is measured with a temperature sensor 1402, and the measured value 130 is sent to a distance measurement device 115, thereby correcting the change in optical path length due to the heat of the optical fiber. With this configuration, the optical path length difference of the reference optical system that serves as the distance standard can be obtained with high precision, enabling highly accurate distance measurement. [Example]

[0057] FIG. 15a shows an example of the configuration of a distance measurement device 100 according to an eighth embodiment of the present invention. While FIG. 12 uses a polarization switch 1201 to switch the measurement direction, an optical switch 1501 is used instead. Light L1 irradiated from a laser light source 101 and passed through an optical coupler 103 is split into two optical paths by the optical switch 1501. A polarizer 801A is inserted into one of the optical paths. The light is then guided to a polarization beam combiner 802. A polarizer 801B is also inserted into the other optical path. The fast axis and slow axis of the optical fiber for the light that has passed through the polarizer 801B are inverted and fused to the polarization beam combiner 802. This makes it possible to separate the light split into two by the optical switch 1501 into components with different polarizations. The optical switch 1501 mechanically switches the optical paths, and therefore has the characteristic of not causing leakage of polarized light. Therefore, a high extinction ratio can be maintained compared to a configuration using a polarization beam combiner.

[0058] Figure 15b shows a configuration in which the insertion position of the optical switch is changed from that of Figure 15a. In Figure 15b, by placing optical switch 1501 after the circulator, it is possible to irradiate the measurement object with light at an extinction ratio determined by polarizers 108A and 108B and polarization beam combiner 802, without relying on the extinction ratios of coupler 109 and circulator 111. Furthermore, in this configuration, only one type of polarization passes up to optical switch 1501, so by inserting polarizers 108C and 108D into the interferometer, the effects of leakage light can be reduced. [Example]

[0059] Next, configuration examples of a shape measurement device will be described in accordance with Examples 9 to 13 with reference to FIGS.

[0060] First, Fig. 16 is a diagram showing an example of the configuration of a distance measurement system according to a ninth embodiment of the present invention. Light emitted from distance measurement device 100 is guided by an optical fiber and emitted into space from optical fiber focuser 1600. The beam is scanned using beam scanning mechanisms 1601 and 1602, and is scanned two-dimensionally on object 114. A galvanometer mirror may be used as the beam scanning mechanism to scan the beam. Using one galvanometer mirror allows for one-dimensional scanning, and using two galvanometer mirrors allows for two-dimensional scanning. Alternatively, other mechanisms capable of deflecting and scanning light, such as a MEMS mirror or a polygon mirror, may be used as the scanning mechanism. [Example]

[0061] 17 is a diagram showing an example of the configuration of a distance measurement system according to a tenth embodiment of the present invention. Light emitted from a distance measurement device 100 is guided to a measurement head 1700 by an optical fiber 1701. The light guided into the measurement head 1700 is emitted into space from an optical fiber focuser 1702. A probe shaft 1704 is attached to a rotary motor 1703, and a prism 1705 is attached to the tip of the probe shaft. The light reflected by 1705 is irradiated onto a measurement object 1706, and the reflected light is reflected again by prism 1705 and collected by optical fiber focuser 1702. Rotation of rotary motor 1703 rotates prism 1705 at the tip, making it possible to measure the cross-sectional shape of object 1706. [Example]

[0062] 18 is a diagram showing an example of the configuration of a distance measurement system according to an eleventh embodiment of the present invention. Light emitted from the distance measurement device 100 is guided to a measurement head 1700 by an optical fiber 1701, and is then emitted into space from an optical fiber focuser 1702. The linearly polarized light guided from the distance measurement device 100 is converted into circularly polarized light by a λ / 4 plate 1707, and then passes through a λ / 4 plate 1708 attached to a rotary motor 1703, where it becomes linearly polarized again. The light is reflected or transmitted by a polarizing beam splitter 1705 attached to the tip of a probe 1704 according to the polarization direction, and is irradiated onto the measurement target 114, 1141. At this time, by switching the polarization using a polarization switcher 1201 mounted on the distance measurement device 100 in FIG. 4, it is possible to switch the direction between side measurement and depth measurement.

[0063] Figure 19 explains the principle of switching the measurement direction using polarized light at the tip of the probe. The polarized beam splitter 1705 at the tip of the probe has the property of transmitting light that vibrates parallel to the plane of incidence (P-polarized light) and reflecting light that vibrates perpendicular to the plane of incidence (S-polarized light). Therefore, by electrically switching the polarization of the ranging laser between P-polarized light and S-polarized light using polarization switcher 1201, the direction of ranging laser irradiation can be switched between the lateral direction and the depth direction.

[0064] To rotate the measurement beam while keeping it facing sideways, it is necessary to rotate the polarization direction of the incident light 1901 in accordance with the rotation of the polarizing beam splitter, and to keep the polarization state relative to the polarizing beam splitter constant.

[0065] For this reason, two λ / 4 plates 1707 and 1708 are used. Linearly polarized light is converted into circularly polarized light by positioning the axis of the first λ / 4 plate 1707 at 45 degrees to the polarization direction of the incident light 1901. The second λ / 4 plate 1708 and polarizing beam splitter 1705 are attached to a rotary motor and rotate together with the motor. By passing through the second λ / 4 plate 1708, the circularly polarized light is converted back into linearly polarized light, and as the motor rotates, a constant polarized incident direction is always maintained for the polarizing beam splitter 1705, making it possible to rotate the beam directed in the lateral direction. [Example]

[0066] Figure 20 is a diagram showing an example of the configuration of a distance measurement system according to a twelfth embodiment of the present invention. Figure 20 shows an example of a configuration including a scanning mechanism that scans a distance measurement head 1700. By mounting the distance measurement head 1700 on a Z-axis stage 2006, the measurement head 1700 can be moved up and down. Furthermore, the measurement target 114 is mounted on an X-axis stage 2004 and a Y-axis stage 2005, and the measurement target 114 can be moved in the horizontal direction. After positioning the measurement target 114 in the horizontal direction relative to the measurement head 1700, the measurement head 1700 can be moved in the vertical direction to measure the three-dimensional shape of the measurement target 114.

[0067] These moving stages are driven by a stage controller 2008 via wiring 2007. The stage controller 2008 is controlled by the control PC 116.

[0068] As an example of a scanning mechanism, by holding the measuring head 1700 of the present invention instead of a tool in a three-axis machining center, it is possible to realize on-machine measurement on the machining center. It is also possible to realize a three-dimensional shape measuring device that holds and moves the measuring head 1700 of the present invention with a multi-degree-of-freedom robot and measures the shape of the measurement object 114. Furthermore, if the measurement object range is narrow and the shape can be measured only by moving in the Z-axis direction, the measurement object 114 may be positioned with a jig so that its position is uniquely determined, and measurement may be performed by moving only the Z-axis stage.

[0069] Fig. 21 shows an example of the system configuration of the shape measurement device shown in Fig. 20. The measurement head 1700 is controlled by the distance measurement device 100, and the distance to the measurement object is measured. The distance measured by the distance measurement device 100 is input to a distance calculation unit 2101 in the control PC 116, and the distance measurement value is linked to the rotary stage encoder signal, etc.

[0070] 20, and its position is controlled by a stage controller 2108. The stage coordinates acquired by the stage controller 2108 and the distance measurement results obtained by the distance calculation unit 2101 are processed by a shape calculator 2102, making it possible to measure the three-dimensional shape of the target. The measurement results are displayed on a display unit 117. [Example]

[0071] Figure 22 shows a different embodiment from Figure 18. In FMCW distance measurement, as explained in Figure 12, the light separated by coupler 109 in distance measurement device 100 measures the difference in distance between the light reflected from measurement target 114 and the light combined by coupler 110. Here, after separation by coupler 109, the light path to measurement target 114 changes in the optical path length due to optical fiber elements, etc., due to the influence of heat, etc., along the way, resulting in measurement errors. Therefore, it is conceivable to correct the distance origin in order to improve measurement accuracy.

[0072] As an example of distance origin correction, a reflective coating 2200 for generating a distance origin is applied to the incident surface of the polarizing beam splitter 1705. Polarizing beam splitters are generally made of glass, and if no coating is applied, the surface reflectance will be about 4%. Although it depends on the sensitivity of the photoreceiver used, if the reflectance is too high and the photoreceiver is saturated, it is necessary to adjust the reflectance to 4% or less using a surface coating. Furthermore, reflections on the polarizing beam splitter exit surfaces 2201 and 2202 cause noise, so they must be minimized as much as possible. Therefore, an anti-reflection coating is applied. A typical anti-reflection coating has a reflectance of 0.1% or less.

[0073] Figure 23 shows the FFT result of the detected beat signal obtained with the configuration of Figure 22. The measurement peak of the incident surface of polarized beam splitter 1705 used as the distance origin is designated as 2301. On the other hand, the measurement peak from measurement object 114 after passing through the polarized beam splitter is designated as 2302. By subtracting the peak distance of 2301 from the peak distance of 2302, it is possible to perform distance origin correction.

[0074] FIG. 24 shows the process flow for origin correction. In process step S2400, it is determined whether side measurement or depth measurement is being performed. In the case of side measurement, a beat signal is acquired in process step S2401. In addition, an encoder signal of the rotary motor, whose acquisition timing is synchronized with that of the beat signal, is acquired. In process step S2402, the distance to the measurement object and the distance to the origin are calculated. In process step S2403, the measurement object distance after origin correction is calculated by subtracting the origin distance from the measurement object distance. Furthermore, in process step S2404, the diameter of the object is calculated from the target distance after origin correction and the encoder signal of the rotary motor synchronized thereto. It is possible to calculate not only the diameter but also the circularity. Furthermore, by combining this with the measurement head scanning coordinates described in FIG. 20, it is also possible to calculate a three-dimensional shape.

[0075] In the case of depth measurement, a beat signal is acquired in processing step S2405. The distance to the measurement object and the distance to the origin are calculated in processing step S2406. The measurement object distance after origin correction is calculated by subtracting the origin distance from the measurement object distance in processing step S2407. In addition, by combining this with the measurement head scanning coordinates described in Figure 20, it is also possible to calculate a three-dimensional shape. [Example]

[0076] In the configuration of Example 1, a polarizer was used to transmit only specific polarization components, but an example configuration using something other than a polarizer is shown in Figure 25. Light emitted from optical fiber 2501a is collimated by lens 2502a and irradiated onto polarizing beam splitter 2503. Polarizing beam splitter 2503 separates the light based on the polarization direction, transmitting one polarized light and reflecting the other polarized light. The reflected light is absorbed by absorber 2506, and the transmitted light is guided by lens 2502b to optical fiber 2501a, thereby achieving an effect equivalent to that of a polarizer.

[0077] Furthermore, an element having birefringence may be used as an element that separates light according to the polarization direction. An example using an element having birefringence is shown in Fig. 26. Light emitted from optical fiber 2501a is collimated by lens 2502a and irradiated onto element 2601 having birefringence. The refractive index of light passing through 2601 differs depending on the polarization, resulting in a difference in the angle of travel. Therefore, by absorbing one polarized light with absorber 2506 and guiding the other polarized light to optical fiber 2501b by lens 2502b, it is possible to achieve an effect equivalent to that of a polarizer. [Example]

[0078] In the configuration of Example 4, a polarized beam splitter / polarized beam combiner is used to separate / combine polarized light and create an optical path difference between the polarized components. However, a configuration in which an element having birefringence is used to separate / combine light according to the polarization direction may also be used. FIG. 27 shows an example in which an element having birefringence is used. Light emitted from optical fiber 2501a is collimated by lens 2502a and irradiated onto element 2601a having birefringence. Since the refractive index of light passing through 2601a differs depending on the polarization, a difference occurs in the angle of travel. Therefore, one polarized light is guided to optical fiber 2501b by lens 2502b, and the other polarized light is guided to optical fiber 2501c by lens 2502c. Here, optical fibers 2501b and 2501c have different lengths. Light emitted from optical fiber 2501b is collimated by lens 2502d and irradiated onto element 2601b having birefringence. Furthermore, the light emitted from optical fiber 2501c is collimated by lens 2502e and irradiated onto element 2601b having birefringence. Both beams are combined again onto the same optical path by element 2601b having birefringence, and are guided to optical fiber 2501d by lens 2502f. This configuration provides the same function as a polarized beam splitter / polarized beam combiner. [Example]

[0079] In Examples 1 to 8, an example configuration using optical fibers is shown as one example, but it may also be a system that configures an interferometer in space using optical elements that branch and combine light in space.

[0080] Furthermore, the system may be a system using a photonic integrated circuit in which waveguides, couplers, circulators, polarizing elements (polarizers, polarized beam splitters), and detectors are formed on a substrate, and some or all of the optically necessary elements and functions for realizing the embodiments described in Examples 1 to 8 are formed on the substrate. [Explanation of symbols]

[0081] 100: distance measurement device, 101: semiconductor laser, 102: oscillator, 103, 104, 106, 109, 110: optical fiber coupler, 105: optical fiber, 107: photodetector, 108: polarizer, 111: circulator, 112: optical fiber focuser, 113: photodetector, 114, 1141: measurement object, 115: distance measurement device control unit, 116: control device, 117: display unit, 201: reference light, 202: measurement light, 301: FFT peak waveform, 401: beat signal obtained by polarization component of main component, 402: beat signal obtained by polarization component of leakage light, 40 3: FFT intensity profile obtained by the polarization component of the main component, 404: FFT intensity profile obtained by the polarization component of the leaked light, 405: FFT intensity profile obtained by combining the polarization components of the main component and the leakage light, 406: Distance measurement value obtained when no thermal fluctuation occurs, 407: Distance measurement value obtained when thermal fluctuation occurs, 408: Distance measurement value obtained when thermal fluctuation occurs, 601: Beat signal obtained by the polarization component of the main component, 602: Beat signal obtained by the polarization component of the leaked light, 603: FFT intensity profile obtained by the polarization component of the main component profile, 604: FFT intensity profile obtained by the polarization component of the leakage light, 605: FFT intensity profile obtained by combining the main component and the polarization component of the leakage light, 606: Distance measurement value obtained when no thermal fluctuation occurs, 607: Distance measurement value obtained when thermal fluctuation occurs, 608: Distance measurement value obtained when thermal fluctuation occurs, 801: Polarizing beam splitter, 802: Polarizing beam combiner, 901: FFT intensity profile obtained by the polarization component of the main component, 902: FFT intensity profile obtained by the polarization component of the leakage light, 903: Distance measurement value obtained when thermal fluctuation occurs Distance measurement value obtained when this does not occur, 1201: polarization switch, 1202: polarization beam splitter, 1401: heat insulating box, 1402: temperature sensor, 1501: optical switch, 1600: optical fiber focuser, 1601: beam scanner, 1602: beam scanner, 1700: measurement head, 1701: optical fiber, 1702: optical fiber focuser, 1703: rotation motor, 1704: shaft, 1705: polarization beam splitter, 1707: λ / 4 plate, 1708: λ / 4 plate, 1901: laser light, 2004: X-axis stage, 2005: Y-axis stage,2006: Z-axis stage, 2007: distribution cable, 2008: stage controller, 2101: distance calculation unit, 2102: shape calculation unit, 2103: stage mechanism, 2200: reflective coating, 2201: anti-reflection coating, 2202: anti-reflection coating, 2301: distance origin detection peak, 2302: target detection peak, 2501: optical fiber, 2502: lens, 2503: polarized beam splitter, 2506: absorbing material, 2601: element with birefringence,

Claims

1. A distance measurement method comprising: splitting light generated by a laser light source into a reference optical system and a measurement optical system; detecting a reference optical path measurement beat signal from the reference light that has passed through the reference optical system; detecting a measurement optical path measurement beat signal from measurement light obtained in the measurement optical system by passing through a measurement object; and measuring a distance to the measurement object based on the measurement optical path measurement beat signal and the reference optical path measurement beat signal, A distance measurement method characterized in that an element for reducing polarization-induced distance errors is installed in either one or both of the reference optical system and the measurement optical system.

2. 2. The distance measurement method according to claim 1, A distance measurement method characterized in that the polarization-induced distance error reduction element is an orthogonal polarization component attenuation element that transmits a specific linear polarization component of light generated by a laser light source and attenuates the polarization component orthogonal to it.

3. 2. The distance measurement method according to claim 1, A distance measurement method characterized in that the polarization-induced distance error reduction element is a polarization component optical path difference generating element having an element that creates an optical path difference between a specific linearly polarized component of light generated by a laser light source and a polarized component orthogonal to it.

4. 4. The distance measurement method according to claim 3, A distance measurement method characterized in that the optical path difference between a specific linearly polarized component of light generated by a laser light source and a polarized component orthogonal to it is equal to or greater than the line width of a spectral peak obtained by Fourier transforming the measurement optical path measurement beat signal.

5. 2. The distance measurement method according to claim 1, A distance measurement method characterized by installing a polarization switching element that switches the polarization of light generated by a laser light source within either the reference optical system or the measurement optical system, or within both optical systems, and an element that switches the irradiation direction onto the object depending on the polarization direction.

6. 2. The distance measurement method according to claim 1, A distance measurement method comprising storing at least a part of the reference optical system in a storage box, measuring the temperature of the storage box, and using the temperature to correct for changes in the optical path length due to the temperature of the reference optical system.

7. a measurement optical system that guides the other branched light to obtain a reference light that serves as a reference for distance; a first light-receiving unit that receives the reference light that has passed through the reference optical system and detects a reference light path measurement beat signal; and a second light-receiving unit that receives the measurement light reflected by the object to be measured in the measurement optical system and detects the measurement light path measurement beat signal, and the distance measurement device measures the distance to the object to be measured based on the measurement light path measurement beat signal and the reference light path measurement beat signal, A distance measurement device characterized in that a polarization-induced distance error reduction element is installed in either one or both of the reference optical system and the measurement optical system.

8. a measurement optical system that receives the other branched light and obtains reflected light from the measurement object as measurement light; a first light-receiving unit that receives the reference light that has passed through the reference optical system and detects a reference light path measurement beat signal; and a second light-receiving unit that receives the measurement light reflected by the measurement object in the measurement optical system and detects the measurement light path measurement beat signal, and the distance measurement system measures the distance to the measurement object based on the measurement light path measurement beat signal and the reference light path measurement beat signal, A polarization-induced distance error reduction element is provided in either one or both of the reference optical system and the measurement optical system, A distance measurement system characterized in that, when irradiating the measurement object with irradiation light in the measurement optical system, the system comprises a scanning mechanism for scanning the irradiation light one-dimensionally, two-dimensionally, or three-dimensionally.

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