Distance measuring device, distance measuring system, and distance measuring method

Abstract

The present invention provides a distance measuring device, system, and method capable of reducing distance errors caused by polarization. [Solution] When the irradiation light generated by the laser light source passes through the measurement optical system, the polarization direction of the irradiation light is changed by a predetermined angle by the polarization switching unit. When the measurement light reflected by the object to be measured passes through the optical system, the polarization direction of the measurement light is changed by a predetermined angle by the polarization switching unit. The two orthogonal polarization components of the measurement light are separated by the polarization separation unit. A measurement beat signal is detected using the measurement light, and the distance from the measurement beat signal to the object to be measured is measured.

Description

Technical Field

[0001] The present invention relates to a distance measurement device, a distance measurement system, and a distance measurement method for non-contact measurement of the distance to an object using light.

Background Art

[0002] As a technique for measuring the distance to an object non-contact using light and switching the emission direction of light by switching the polarization direction of light, Patent Document 1 discloses "light generated by a laser light source is branched into a reference optical system and a measurement optical system, a reference optical path measurement beat signal is detected from the reference light that has passed through the reference optical system, a measurement optical path measurement beat signal is detected from the measurement light obtained via the measurement object in the measurement optical system, and based on the measurement optical path measurement beat signal and the reference optical path measurement beat signal, a distance measurement method for measuring the distance to the measurement object, and a polarization-induced distance error reduction element is installed in either one or both of the reference optical system and the measurement optical system".

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the technology for measuring the distance to an object non-contact using light, as described in Patent Document 1, there is a problem that when the ambient temperature changes and the temperature of the optical fiber constituting the distance measurement unit changes, the polarization state of the light passing through the optical fiber changes, causing distance errors in the optical interference signal. Therefore, in order to reduce the distance error caused by polarization, a configuration is adopted in which a distance difference is created between two orthogonal polarization components. However, in order to create a distance difference between two orthogonal polarization components, the two polarizations must be separated once, a distance difference is created, and then they are combined again, which presents another problem as it complicates the configuration of the optical system.

[0005] Therefore, the present invention aims to provide a distance measurement method, a distance measurement device, and a distance measurement system that can be constructed with a small number of parts without complicating the optical system, and that can further reduce distance errors caused by polarization. [Means for solving the problem]

[0006] The present invention includes several means for solving at least part of the above problems, but an example is as follows: A distance measuring device for measuring the distance to a measurement target, comprising a laser light source, a measuring optical system that detects a measurement beat signal by passing irradiation light generated by the laser light source through it and by passing measurement light reflected by the measurement target through the irradiation light, and a measuring unit that measures the distance from the measurement beat signal to the measurement target, wherein the measuring optical system comprises a polarization separation unit that separates two orthogonal polarization components in light and outputs them to different optical paths, and a polarization switching unit that changes the polarization direction of light, wherein when the irradiation light passes through the measuring optical system, the polarization separation unit passes the irradiation light through it, and the polarization switching unit changes the polarization direction of the irradiation light that has passed through the polarization separation unit by a predetermined angle, and when the measurement light passes through the measuring optical system, the polarization switching unit changes the polarization direction of the measurement light by a predetermined angle, and the polarization separation unit separates the two orthogonal polarization components of the measurement light whose polarization direction has been changed by the polarization switching unit. [Effects of the Invention]

[0007] According to the present invention, the optical system can be constructed with a small number of parts, and even when the ambient temperature of the distance measuring unit changes, it is possible to suppress polarization-induced distance errors, thereby enabling accurate measurement of the distance to the target.

[0008] Other issues, configurations, and effects not mentioned above will be clarified by the following description of embodiments for carrying out the invention. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the configuration of a distance measuring device according to the first embodiment. [Figure 2] This diagram shows the principle of the FMCW method. [Figure 3A] This figure shows an example of the measurement beat signal L4 detected by the light receiver 113. [Figure 3B] This figure shows the results obtained by performing an FFT on the measured beat signal L4. [Figure 4A] This figure shows an example of the measurement beat signal L4 detected by the light receiver 113. [Figure 4B] This figure shows the results obtained by performing an FFT on beat signals 401 and 402. [Figure 4C] This figure shows the distance measurement error that occurs when a temperature change, such as heat, is applied to an optical fiber. [Figure 5A] This is an explanatory diagram of the mechanism for reducing distance measurement errors in the first embodiment. [Figure 5B] This is an explanatory diagram of the mechanism for reducing distance measurement errors in the first embodiment. [Figure 6] This figure shows an example of the configuration of a distance measuring device according to the second embodiment. [Figure 7] This figure shows an example of the configuration of a distance measuring device according to the third embodiment. [Figure 8] This figure shows a modified example of the configuration of the distance measuring device according to the third embodiment. [Figure 9A] This is an explanatory diagram of the mechanism for reducing distance measurement errors in the fourth embodiment. [Figure 9B] It is an explanatory diagram of a mechanism for reducing distance measurement errors in the fourth embodiment. [Figure 10] It is a diagram showing an example of the configuration of a distance measurement system according to the fifth embodiment. [Figure 11] It is a diagram showing an example of the configuration of a distance measurement system according to the sixth embodiment. [Figure 12] It is a diagram showing an example of the configuration of a distance measurement system according to the seventh embodiment. [Figure 13] It is a diagram showing the principle of switching the irradiation direction of irradiation light using polarization at the probe tip in the seventh embodiment. [Figure 14] It is a diagram showing an example of the configuration of a distance measurement system according to the eighth embodiment. [Figure 15] It is a diagram showing an example of the system configuration of a distance measurement system according to the eighth embodiment. [Figure 16] It is a diagram showing an example of the configuration of a distance measurement system according to the ninth embodiment. [Figure 17] It is a diagram showing the FFT result of a measurement beat signal in the ninth embodiment. [Figure 18] It is a diagram showing an example of the processing flow of distance origin correction in a distance measurement device.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments are examples for explaining the present invention, and for the sake of clarity of explanation, appropriate omissions and simplifications have been made. The present invention can also be implemented in various other forms. Unless otherwise limited, each component may be singular or plural.

[0011] The positions, sizes, shapes, ranges, etc. of each component shown in the drawings may not represent the actual positions, sizes, shapes, ranges, etc. for the purpose of facilitating understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, ranges, etc. disclosed in the drawings.

[0012] When there are multiple components with the same or similar function, they may be described using the same symbol but with different subscripts. Furthermore, if it is not necessary to distinguish between these multiple components, the subscripts may be omitted in the description.

[0013] In embodiments, processing performed by executing a program may be described. Here, the computer executes the program using a processor (e.g., CPU, GPU) and performs processing defined by the program using memory resources (e.g., memory) and interface devices (e.g., communication ports). Therefore, the main entity performing the processing by executing the program may be the processor. Similarly, the main entity performing the processing by executing the program may be a controller, device, system, computer, or node having a processor. The main entity performing the processing by executing the program may be an arithmetic unit, and may include dedicated circuits that perform specific processing. Here, dedicated circuits include, for example, FPGAs (Field Programmable Gate Arrays), ASICs (Application Specific Integrated Circuits), CPLDs (Complex Programmable Logic Devices), etc.

[0014] The program may be installed on the computer from the program source. The program source may be, for example, a program distribution server or a storage medium readable by the computer. If the program source is a program distribution server, the program distribution server includes a processor and storage resources for storing the program to be distributed, and the processor of the program distribution server may distribute the program to other computers. In addition, in some embodiments, two or more programs may be implemented as a single program, or one program may be implemented as two or more programs.

[0015] In the following descriptions of embodiments of the present invention, examples of applying the present invention to optical fiber optical systems will be described, but the present invention is also applicable to conventional bulk optical systems. [Examples]

[0016] Figure 1 shows an example of the configuration of a distance measuring device according to the first embodiment. The distance measuring method using optical path difference here is based on the FMCW (Frequency Modulated Continuous Wave) method. In Figure 1, the distance measuring device 100 includes a laser light source 101, an oscillator 102, optical fiber couplers 103, 104, 106, 108, 109, photodetectors 107, 113, a polarizing beam combiner 110, a polarizing switch 111, a fiber focuser 112, and a distance measuring control unit 117. The distance measuring control unit 117 is connected to an external control PC (information processing device such as a personal computer (PC) or server device) 118.

[0017] In the FMCW distance measuring device 100, the distance measurement control unit 117 first transmits a swept waveform signal (e.g., a triangular wave signal) to the oscillator 102. Based on the received swept waveform signal, the oscillator 102 injects a triangular wave current into the laser light source 101 and modulates the drive current. As a result, the laser light source 101 generates FM (Frequency Modulated) light that is frequency-swept in time at a constant modulation rate. Alternatively, 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-shaped control signal from the oscillator 102. As a result, FM light that is frequency-swept in time is generated from the laser light source 101.

[0018] Next, the generated FM light is split into light L1 and light L2 by the optical fiber coupler 103. Note that optical fiber couplers 103, 104, 106, 108, and 109 are devices that split (demultiplex) and merge (combin) light, and may also be beam splitters. Optical fiber couplers 104, 106, optical fiber 105, and photodetector 107 constitute a reference optical system, and light L2, which was split by optical fiber coupler 103, is guided to the reference optical system. Light L2 is further split into light L21 and light L22 by optical fiber coupler 104. After a certain optical path difference is set in the optical fiber 105, the split light L21 and light L22 are combined by optical fiber coupler 106 and received by photodetector 107. Furthermore, this configuration of optical fiber couplers 104, 106 and optical fibers 105 with different optical path lengths constitutes a Mach-Zehnder interferometer, and the photodetector 107 detects a constant beat signal (reference beat signal) L3 that is proportional to the optical path difference.

[0019] The optical fiber couplers 108 and 109, the polarizing beam combiner 110, the polarization switcher 111, and the photodetector 113 constitute the measurement optical system. The other optical fiber L1, which is branched by the optical fiber coupler 103, is guided into the measurement optical system. Optical fiber L1 is branched into optical fiber L11 and optical fiber L12 by the optical fiber coupler 108. One of the optical fibers L11, branched by the optical fiber coupler 108, becomes the reference light and goes to the optical fiber coupler 109. The other optical fiber L12 becomes the illumination light, passes through the polarizing beam combiner 110, and its polarization direction is controlled by the polarization switcher 111 (it becomes illumination light with a changed polarization direction from optical fiber L12), and it is emitted into space from the fiber focuser 112. The illumination light emitted into space has its emission direction switched according to the polarization direction by the polarizing beam splitter 114, which is located outside the distance measuring device 100, and is irradiated onto the measurement target 115 or the measurement target 116.

[0020] The light L12A reflected from the object to be measured 115 or 116 (hereinafter referred to as reflected light or measurement light) passes through the fiber focuser 112 and the polarization switcher 111 again, passes through the other port of the polarization beam combiner 110, and is combined with the reference light L11 at the optical fiber coupler 109. As will be described later, the reference light L11 and the measurement light L12A interfere with each other, and as a result, the beat signal (measurement beat signal) L4 generated by the interference between the reference light L11 and the measurement light L12A is detected by the photodetector 113.

[0021] The distance measurement control unit 117 uses the reference beat signal L3 received by the photodetector 107 as a sampling clock to perform A / D conversion on the measurement beat signal L4 received by the photodetector 113. Alternatively, it samples the reference beat signal L3 and the measurement beat signal L4 at a constant sampling clock. More specifically, by performing a Hilbert transform on the reference beat signal L3, a signal with a 90-degree phase shift can be created. Since the local phase of the signal can be determined from the signals before and after the Hilbert transform, the timing at which the reference beat signal L3 has a constant phase can be determined by interpolating this phase.

[0022] By interpolating and sampling the measurement beat signal L4 at this timing, it becomes possible to resample the measurement beat signal L4 with reference to the reference beat signal L3. Alternatively, the same effect can be achieved by sampling the measurement beat signal L4 using the reference beat signal L3 as the sampling clock in the AD / DA converter of the distance measurement control unit 117 and performing A / D conversion. Details of the distance calculation method from the beat signal will be explained using Figures 2 and 3, but the distance measurement data analyzed by the distance measurement control unit 117 is transmitted to the control PC 118 and displayed on the display unit 119.

[0023] Figure 2 shows the principle of the FMCW method. We will use Figure 2 to explain the analysis of the measurement beat signal. In the graph shown in Figure 2, the horizontal axis is time and the vertical axis is optical frequency. There is a difference Δt in the arrival time of the reference light 201 (L11), which is branched by the optical fiber coupler 108 in Figure 1 and received by the receiver 113 as reference light, and the measurement light 202 (L12A), which is reflected by the measurement target 115 or measurement target 116 and received by the receiver 113. However, the frequency of the laser light source 101 changes during this Δt, so the beat frequency f is equal to the frequency difference caused by this change. b The measurement beat signal L4 is detected by the photodetector 113. 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 object being measured is half the distance light travels in Δt, it can be calculated using the speed of light c in the atmosphere as shown in equation (2).

[0024]

number

[0025]

number

[0026] Distance L and beat frequency have a linear relationship. Therefore, by performing an FFT (First Fourier Transform) on the measurement beat signal L4 detected by the photodetector 113 to determine the peak position and magnitude, the reflection position and amount of reflected light of the measurement target can be determined. Figures 3A and 3B show an example of the measurement beat signal L4 and the reflection intensity profile obtained by performing an FFT on that signal. Figure 3A is a diagram showing an example of the measurement beat signal L4 detected by the photodetector 113. The frequency of the measurement beat signal L4 is proportional to the distance to the measurement target. Figure 3B is a diagram showing the result obtained by performing an FFT on the measurement beat signal L4. In Figure 3B, if the horizontal axis is the frequency of the FFT and the vertical axis is the detected intensity, each point (black circle) in Figure 3B indicates the intensity of reflected light (reflection intensity) as a function of frequency (i.e., distance). As shown in Figure 3B, the data around the peak point 301 is discrete. Here, the peak width w is calculated with distance resolution cT / 2Δν. Therefore, as shown in Figure 3B, by fitting a function such as a quadratic function or a Gaussian function using 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 object being measured with an accuracy greater than the distance resolution. Although FFT was given as an example of beat frequency analysis, the peak position can also be detected with higher resolution than FFT by using, for example, the maximum entropy method.

[0027] Figures 3A and 3B show, as an example, ideal results obtained when distance measurement is performed using only a specific polarization component. In reality, leakage light with a polarization direction perpendicular to a specific polarization component occurs within the optical fiber. This leakage light occurs, for example, due to a low extinction ratio of the optical elements of the optical fiber. Alternatively, it occurs when using optical fiber connectors, as the extinction ratio decreases due to the fit between the connectors. Since the extinction ratio is the ratio of the intensities of the polarization components, if the extinction ratio is high, leakage light will not occur or will be negligible. However, if the extinction ratio is low, the intensity of the leakage light becomes relatively high and cannot be ignored.

[0028] Figures 4A, 4B, and 4C show the measurement beat signal waveforms obtained when stray light occurs. Figure 4A is a diagram showing an example of the measurement beat signal L4 detected by the photodetector 113. In Figure 4A, 401 is the beat signal obtained by the polarization component that is originally to be measured, and 402 is the beat signal obtained by the stray light component that is orthogonal to it. The amplitude ratio of beat signal 401 and beat signal 402 is about the same as the extinction ratio. That is, if the extinction ratio is low, the amplitude ratio will also be low (the difference in amplitude will be small), and conversely, the extinction ratio can be determined by measuring the amplitude ratio. Also, if the polarization component that is originally to be measured passes through the slow axis of the optical fiber, and the stray light component that is orthogonal to it passes through the fast axis of the optical fiber, then beat signal 401 and beat signal 402 will have a distance difference corresponding to the distance they travel through the slow axis and fast axis of the optical fiber, respectively. For example, in Figure 1, assume that the interference origin of the FMCW method exists between the fiber focuser 112 and the measurement target 115 or measurement target 116. Here, the interference origin refers to the position where the distance difference between the reference light 201 and the measurement light 202, as shown in Figure 2, is equal. For example, suppose the distance from the fiber focuser 112 to the interference origin is 200 mm. In that case, the optical fiber length of the reference optical path that is equal to that length is 200 mm × 2 (round-trip optical 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 at which the wavelengths of light passing through the Fast axis and Slow axis are shifted by one period) is 5 mm, then the optical path difference of the light passing through the Fast axis and Slow axis will be 300 mm ÷ 5 mm × 1.55 μm = 93 μm.

[0029] Figure 4B shows the results obtained by performing an FFT on the beat signals 401 and 402 shown in Figure 4A. In Figure 4B, 403 shows the displacement of the reflected intensity with respect to frequency (i.e., distance) obtained by performing an FFT on the component of beat signal 401 (passing through the slow axis of the optical fiber) (hereinafter referred to as the peak intensity), and 404 shows the peak intensity obtained by performing an FFT on the component of beat signal 402 (transmitting through the fast axis of the optical fiber). 405 shows the combined component obtained by combining peak intensity 403 and peak intensity 404.

[0030] If the optical fiber is subjected to temperature changes such as heat, for example, if the ambient temperature around the distance measuring device 100 changes and the temperature of the optical fiber constituting the distance measuring device 100 changes (e.g., rises), stress acts on the optical fiber, causing a change in the phase of the component passing through the Fast axis relative to the component passing through the Slow axis. As a result, the phase of peak intensity 404 relative to peak intensity 403 changes. In this case, if the peak width determined by the frequency sweep width (w shown in Figure 3b) is wider than 93 μm (the optical path difference between the Slow axis and the Fast axis of the optical fiber), the tails of peak intensity 403 and peak intensity 404 overlap, causing the peak position of the composite component 405 to change and creating a difference from the peak position of peak intensity 403. Therefore, a distance measurement error occurs.

[0031] Figure 4C shows the distance measurement error that occurs when a temperature change, such as heat, is applied to an optical fiber. In Figure 4C, the horizontal axis represents the true distance, the vertical axis represents the measured distance, and 406 represents the measured distance obtained in the ideal case where there is no light leakage into the Fast axis. As described above, when a temperature change is applied to the optical fiber due to changes in the ambient temperature, etc., an offset variation in distance occurs. The amount of offset variation differs depending on the phase state of the Fast axis relative to the Slow axis, but for example, in a certain phase, the measured distance becomes larger than the true distance as shown in 407, and in a certain phase, the measured distance becomes smaller than the true distance as shown in 408.

[0032] Therefore, in the distance measuring device 100 of the first embodiment, as shown in Figure 1, a polarizing beam combiner 110 is inserted into the optical path on the optical L12 side, and then a polarization switcher 111 is inserted thereafter to reduce distance measurement errors due to temperature changes in the optical fiber.

[0033] Figures 5A and 5B are explanatory diagrams illustrating the mechanism by which the polarization beam combiner 110 and the polarization switcher 111 reduce distance measurement errors. Using these figures, we will specifically explain how to reduce polarization-induced errors by combining the polarization beam combiner 110 and the polarization switcher 111 in this order.

[0034] Figure 5A shows the case where the polarization direction is switched by the polarization switch 111, causing the irradiated light to be transmitted to the polarization beam splitter 114. The light incident on the slow axis port of the polarization beam combiner 110 contains a main component of polarization according to the slow axis and a leak light component orthogonal to it. In the polarization switch 111, the applied voltage causes the polarization of the light incident on the polarization switch 111 to rotate by 45° due to the Faraday effect. In the polarization switch 111, the optical fiber on the output side (fiber focuser side in Figure 5A) is rotated by 45° relative to the optical fiber connected to the input side (polarization beam combiner side in Figure 5A), that is, the slow axis of the output optical fiber is parallel to the axis on which the slow axis of the input optical fiber has rotated by 45°. As a result, the light traveling along the slow axis of the input optical fiber is output with its polarization rotated by 45° by the polarization switch 111, and then travels along the slow axis of the output optical fiber and enters the fiber focuser 112. The irradiated light emitted into space from the fiber focuser 112 is polarized in the direction of light transmission to the polarization beam splitter 114 and irradiates the object to be measured 115.

[0035] The light reflected from the object to be measured 115 (measurement light) passes again through the polarizing beam splitter 114, fiber focuser 112, and polarization switch 111. When the measurement light passes through the polarization switch 111, the polarization is rotated by another 45° due to the Faraday effect. As a result, the measurement light has polarization perpendicular to the original irradiated light, that is, the slow axis of the measurement light is rotated 90° relative to the slow axis of the incident light. The polarizing beam combiner 110 is a device that separates two orthogonal polarization components within the extinction ratio range and outputs each polarization component to separate optical paths (optical fibers) from ports corresponding to their polarization direction. When the measurement light that has passed through the polarization switch 111 enters the polarizing beam combiner 110, the main component and the stray light component of the measurement light are separated, and the main component is guided to the Fast axis port and output, and the stray light component is guided to the Slow axis port and output, according to the direction of each polarization. The main component of the measurement light output from the Fast axis port travels along the Fast axis of the optical fiber leading to the optical fiber coupler 109. On the other hand, the stray light component of the measurement light travels along the Slow axis of the optical fiber leading to the optical fiber coupler 108. In this way, it is possible to separate the stray light component from the measurement light.

[0036] In the measurement beat signal obtained by interfering the measurement light, from which the stray light component has been separated, with the reference light, the beat signal 402 due to the stray light component shown in Figure 4A is reduced. Therefore, in the peak intensity obtained by performing an FFT on the measurement beat signal, the positions of the peak intensity 403 relative to the main component and the composite component 405 are extremely close. Consequently, the peak position does not change significantly, and it is possible to reduce polarization-induced errors.

[0037] Figure 5B shows the case where the polarization direction is switched by the polarization switch 111, causing the irradiated light to be reflected by the polarization beam splitter 114. The light incident on the slow axis of the polarization beam combiner 110 contains a main component of polarization according to the slow axis and a stray light component orthogonal to it. In the polarization switch 111, the applied voltage causes the polarization of the light incident on the polarization switch 111 to rotate by -45° due to the Faraday effect. As described above, in the polarization switch 111, the optical fiber on the output side (fiber focuser side in Figure 5A) is rotated by 45° relative to the optical fiber connected to the input side (polarization beam combiner side in Figure 5A), that is, the slow axis of the output optical fiber is parallel to the axis on which the slow axis of the input optical fiber has rotated by 45°. As a result, the light traveling along the slow axis of the input optical fiber is output with its polarization rotated by -45° by the polarization switcher 111, and then travels along the slow axis of the output optical fiber and enters the fiber focuser 112. The irradiated light emitted into space from the fiber focuser 112 is polarized in the direction that the light is reflected by the polarization beam splitter 114, and is irradiated onto the object to be measured 116.

[0038] The light reflected from the object being measured 116 (measurement light) passes again through the polarizing beam splitter 114, fiber focuser 112, and polarization switch 111. When the measurement light passes through the polarization switch 111, the polarization is rotated by another -45° due to the Faraday effect. As a result, the measurement light has polarization orthogonal to the original incident light, that is, the slow axis of the measurement light is rotated by -90° relative to the slow axis of the incident light. When the measurement light that has passed through the polarization switch 111 is incident on the polarizing beam combiner 110, the main component and the stray light component of the measurement light are separated, and the main component is guided to the Fast axis port and output according to the direction of each polarization, and the stray light component is guided to the Slow axis port and output. In this way, it is possible to separate the stray light component from the measurement light within the extinction ratio range of the polarizing beam combiner 110, and as described above, it is possible to reduce polarization-induced errors.

[0039] As explained using Figures 5A and 5B, the measurement light L12A output from the polarization beam combiner 110 travels along the fast axis of the optical fiber leading to the optical fiber coupler 109. On the other hand, the reference light L11 branched at the optical fiber coupler 108 travels along the slow axis of the optical fiber leading to the optical fiber coupler 109. As a result, the reference light L11 and the measurement light L12A do not interfere with each other because their polarization directions are orthogonal. Therefore, in order to cause interference between them, the optical fibers connected to the polarization beam combiner 110 are fused together in advance using a fiber fusion splicer so that the fast axis of the optical fiber connected to the polarization beam combiner 110 matches the slow axis of the optical fiber connected to the optical fiber coupler 109. The fusion point can be any point between the polarization beam combiner 110 and the optical fiber coupler 109. In this way, by fusing the optical fiber connected to the polarization beam combiner 110 with the optical fiber connected to the optical fiber coupler 109, the measurement light L12A output from the polarization beam combiner 110, which travels along the fast axis of the optical fiber, travels along the slow axis of the destination optical fiber after the fusion point and reaches the optical fiber coupler 109. Therefore, the measurement light L12A is combined with the reference light L11 at the optical fiber coupler 109, causing interference.

[0040] Furthermore, as explained using Figures 5A and 5B, the stray light component output from the slow axis port of the polarizing beam combiner 110 travels along the slow axis of the optical fiber leading to the optical fiber coupler 108, passing through the optical fiber coupler 108 and optical fiber coupler 103 in this order (following the path taken by the light generated from the laser light source in reverse), and finally reaching the laser light source 101. However, if so-called backlight is incident on the laser light source 101, it may affect the driving (laser oscillation) of the laser light source 101, and the same applies to the stray light component. Therefore, for example, in the configuration of Figure 1, it is preferable to provide an optical isolator (not shown) between the laser light source 101 and the optical fiber coupler 103 to prevent the stray light component from being incident on the laser light source 101.

[0041] As described above, the distance measuring device in the first embodiment is equipped with a polarizing beam combiner and a polarization switcher along the direction of propagation of light irradiated onto the object to be measured. First, the polarization switcher rotates the polarization direction of the light by 45° (or -45°) before irradiation and after reflection, for a total of 90° (or -90°). Next, the polarizing beam combiner separates the two orthogonal polarizations in the light, thereby separating the stray light from the measurement light. This allows the measurement light, from which the stray light has been separated, to be detected by interfering it with the reference light, and as a result, it is possible to reduce the distance measurement error caused by polarization. [Examples]

[0042] In the first embodiment, an example was described in which the distance measuring device is equipped with a polarizing beam combiner and a polarization switch to separate stray light from the measurement light. In the second embodiment, an example of a distance measuring device configuration that can further reduce stray light in addition to such a configuration will be described. In the following description, explanations that overlap with the first embodiment will be omitted, and only the differences will be described. Figure 6 is a diagram showing an example of the configuration of the distance measuring device according to the second embodiment, and the same reference numerals are used for components that are the same as those in the distance measuring device 100 shown in Figure 1.

[0043] In Figure 6, the distance measuring device 200 has the same configuration as the distance measuring device 100 shown in Figure 1, but with a polarizer 601 inserted in the optical path (optical fiber) between optical fiber coupler 108 and optical fiber coupler 109, and a polarizer 602 inserted in the optical path (optical fiber) between the polarizing beam combiner 110 and optical fiber coupler 109. Polarizers 601 and 602 are orthogonal polarization component attenuation elements that transmit only specific linear polarization components, for example, the main component of the slow axis, and reduce leak light in the fast axis. With this configuration, it is possible to reduce the leak light of the reference light L11 branched by the optical fiber coupler 108, and also to reduce the leak light of the measurement light L12A separated by the polarizing beam combiner 110 with an extinction ratio greater than or equal to the extinction ratio of the polarizing beam combiner 110.

[0044] As described above, the distance measuring device in the second embodiment offers the same effects as the first embodiment, as well as a reduction in stray light in the reference light and a further reduction in stray light in the measurement light. [Examples]

[0045] In the first and second embodiments, configuration examples that can reduce light leakage with respect to the measurement optical system were described. In the third embodiment, in addition to the above, configuration examples that can reduce light leakage with respect to the reference optical system will be described. In the following description, explanations that overlap with the first and second embodiments will be omitted, and only the differences will be described. Figure 7 is an example of the configuration of the distance measuring device according to the third embodiment, and Figure 8 is a diagram showing a modified example of the configuration of the distance measuring device according to the third embodiment. Components identical to those of the distance measuring devices 100 and 200 shown in Figures 1 and 2 are denoted by the same reference numerals. First, in Figure 7, the distance measuring device 300 has the same configuration as the distance measuring device 200 shown in Figure 2, in addition to having a polarizer 701 inserted in the optical path (optical fiber) between the optical fiber coupler 103 and the optical fiber coupler 104.

[0046] Even in the reference optical system, if stray light occurs, distance errors will occur. For example, suppose the length of the optical fiber 105 shown in Figure 7 is 300 mm. Here, if the wavelength of light L2 is 1.55 μm and the beat length of the optical fiber 105 (the distance at which the wavelength of light passing through the Fast axis and Slow axis shifts by one period) is 5 mm, then the optical path difference of the light passing through the Fast axis and Slow axis will be 300 mm ÷ 5 mm × 1.55 μm = 93 μm. As shown in Figure 4A, if a stray light component is generated with respect to the main component of polarization, and the phase of the stray light changes, the resulting beat signal will change. The distance measurement control unit 117 resamples the measurement beat signal L4 obtained in the measurement optical system based on the reference beat signal L3 obtained in the reference optical system. For example, as explained in the first embodiment, if a temperature change is applied to the optical fiber 105, the phase of the stray light changes, and as a result the reference beat signal L3 changes, distance errors will occur.

[0047] Therefore, as shown in Figure 7, in the distance measuring device 300, by inserting a polarizer 701 into the optical path (optical fiber) between the optical fiber coupler 103 and the optical fiber coupler 104, it is possible to reduce the leakage light in the light L2 that is the source of the reference beat signal L3. In addition, unlike the measurement optical system, the reference optical system does not need to switch the polarization direction, so it only needs to pass polarization in one direction, and it is possible to sufficiently reduce leakage light using the polarizer 701.

[0048] Furthermore, in the modified configuration shown in Figure 8, in addition to the configuration shown in Figure 7, the optical fiber couplers 104, 106 and optical fiber 105 that constitute the Mach-Zehnder interferometer for generating a reference beat signal that serves as a distance reference are covered by an insulating box 801 in the distance measuring device 300. A temperature sensor 802 is provided inside the insulating box 801, and the temperature inside the insulating box 801 is measured by this temperature sensor 802, and the measured value 803 is sent from the temperature sensor 802 to the distance measuring control unit 117. With this configuration, first, the polarizer 701 reduces light leakage in optical fiber L2, and further, the insulating box 801 suppresses distance errors caused by temperature changes (such as changes in ambient temperature) of the optical fiber 105 that constitute the Mach-Zehnder interferometer.

[0049] As described above, the distance measuring device of the third embodiment offers the same advantages as the first embodiment, but also reduces stray light in the light used to generate the reference beat signal and suppresses temperature changes in the optical fiber. This allows for accurate determination of the optical path difference of the reference optical system, which serves as the distance reference, enabling highly accurate distance measurement. [Examples]

[0050] In the first embodiment, an example of separating stray light from the measurement light using a polarizing beam combiner and a polarization switch was described. In the fourth embodiment, another configuration example of similarly separating stray light from the measurement light will be described. Note that the configuration of the distance measuring device in the fourth embodiment differs from the configuration of the distance measuring device shown in Figures 1, 6, 7, or 8 only in the polarization switch 111. Therefore, the explanation of redundant content will be omitted, and the differences (mechanisms for reducing distance measurement errors) will be described.

[0051] Although not shown in the figures, as described above, the distance measuring device in the fourth embodiment includes a fixed Faraday rotator 901 and a λ / 2 plate 920 attached to a rotating mechanism 903 instead of a polarization switch 111. Figures 9A and 9B are explanatory diagrams of the mechanism by which the polarization beam combiner 110, Faraday rotator 901, and λ / 2 plate 920 reduce distance measurement errors, similar to Figures 5A and 5B, and the same reference numerals are used for components identical to those shown in Figures 5A and 5B.

[0052] Figure 9A shows the case where light is transmitted through the polarizing beam splitter 114 and irradiates the object to be measured 115. Similar to the explanation for Figure 5A, the light incident on the slow axis port of the polarizing beam combiner 110 contains a principal component of polarization according to the slow axis and a stray light component orthogonal to it. The light that has passed through the polarizing beam combiner 110 is incident on the Faraday rotator 901. In the Faraday rotator 901, the polarization direction of the incident light is rotated by 45°. The light that has passed through the Faraday rotator 901 and whose polarization direction has been rotated by 45° is incident on the λ / 2 plate 902 attached to the rotation mechanism 903. At this time, by rotating the λ / 2 plate using the rotation mechanism 903 so that the crystal orientation of the λ / 2 plate faces 157.5° as shown in the figure, the polarization direction of the light passing through the λ / 2 plate rotates by another 45°, resulting in polarization that is orthogonal to the original light (the light at the time it passes through the polarizing beam combiner 110), i.e., the slow axis is rotated by 90°. Note that the rotation control of the rotation mechanism 903 may be performed as needed by the distance measurement control unit 117, etc., when irradiating the object to be measured, or the rotation mechanism 903 may be rotated in advance.

[0053] The irradiated light that has passed through the λ / 2 plate is emitted into space from the fiber focuser 112, passes through the polarizing beam splitter 114, and irradiates the object to be measured 115. The light reflected from the object to be measured 115 (measurement light) passes through the polarizing beam splitter 114 and fiber focuser 112 again and is incident on the λ / 2 plate. When the measurement light passes through the λ / 2 plate, the polarization direction of the measurement light rotates by -45°. After that, the measurement light passes through the Faraday rotator 901, at which point the polarization direction of the measurement light rotates again by 45°. As a result, the polarization direction of the measurement light returns to the state it was in when it was reflected from the object to be measured 115, and the measurement light is incident on the polarizing beam combiner 110 with its slow axis rotated by 90° relative to the original light. In this way, the polarization direction (slow axis) of the main component in the measurement light is rotated by 90° (perpendicular to the slow axis of the original light). As a result, in the polarization beam combiner 110, the main component and stray light of the measurement light are separated, the main component is guided to the fast axis port, and the stray light component is guided to the slow axis port and output. In this way, similar to the polarization switch 111 shown in Figure 5A, it is possible to reduce the stray light component in the measurement light by combining the Faraday rotator 901 and the λ / 2 plate 902.

[0054] Next, Figure 9B shows the case where light is reflected by the polarizing beam splitter 114 and irradiates the object to be measured 116. Similar to the above, when the light that has passed through the polarizing beam combiner 110 passes through the Faraday rotator 901, the polarization direction of the light is rotated by 45°. The light then passes through the λ / 2 plate 902 attached to the rotation mechanism 903. At this time, by rotating the λ / 2 plate using the rotation mechanism 903 so that the crystal orientation of the λ / 2 plate faces 112.5° as shown in the figure, the polarization direction of the light passing through the λ / 2 plate is rotated by -45°, becoming the same as the polarization direction of the original light (the light at the time it passed through the polarizing beam combiner 110).

[0055] The irradiated light that has passed through the λ / 2 plate is emitted into space from the fiber focuser 112, reflected by the polarizing beam splitter 114, and irradiated onto the object to be measured 116. The light reflected from the object to be measured 116 (measurement light) passes through the polarizing beam splitter 114 and fiber focuser 112 again and is incident on the λ / 2 plate. When the measurement light passes through the λ / 2 plate, the polarization direction of the measurement light rotates by 45°. Subsequently, when the measurement light passes through the Faraday rotator 901, the polarization direction of the measurement light rotates by another 45°. As a result, the polarization direction of the measurement light becomes orthogonal to the original light (the slow axis rotates by 90°), and in this state, the measurement light is incident on the polarizing beam combiner 110. In this way, the polarization direction (slow axis) of the main component in the measurement light is rotated by 90° (orthogonal to the slow axis of the original light). As a result, in the polarization beam combiner 110, the main component and stray light of the measurement light are separated, the main component is guided to the fast axis port, and the stray light component is guided to the slow axis port and output. In this way, similar to the polarization switch 111 shown in Figure 5B, it is possible to reduce the stray light component in the measurement light by combining the Faraday rotator 901 and the λ / 2 plate 902.

[0056] As described above, the distance measuring device of the fourth embodiment, by providing a polarizing beam combiner, a Faraday rotator, and a λ / 2 plate along the direction of propagation of the light irradiated onto the object to be measured, makes it possible to separate stray light from the measurement light, similar to the first embodiment. This allows the measurement light, from which the stray light has been separated, to be detected by interfering it with the reference light, and as a result, it is possible to reduce the distance measurement error caused by polarization. [Examples]

[0057] In the first to fourth embodiments, various configuration examples of distance measuring devices were described. In the fifth to ninth embodiments, configuration examples in which such distance measuring devices are applied to shape measuring devices will be described using Figures 10 to 18. In the following description, a configuration example of a shape measuring device to which the distance measuring device 100 is applied will be described, with the distance measuring device according to the first to fourth embodiments as a representative example. Also, in Figures 10 to 18, components identical to those shown in Figures 1 to 9 are denoted by the same reference numerals.

[0058] First, Figure 10 shows an example of the configuration of a distance measurement system according to the fifth embodiment. In Figure 10, the distance measurement system 10 includes a distance measurement device 100 and a measurement head 1000 connected to the distance measurement device 100 via an optical fiber. The measurement head 1000 includes a fiber focuser 112 connected to the optical fiber and beam scanning mechanisms 1001 and 1002. As described above, in the distance measurement system of this embodiment, the fiber focuser 112 is provided in the measurement head 1000, not the distance measurement device 100. The same applies to the distance measurement system of the sixth embodiment and subsequent embodiments.

[0059] In the distance measurement system 10, light (irradiated light) emitted from the distance measurement device 100 is guided to the fiber focuser 112 via an optical fiber and emitted into space from the fiber focuser 112. The measurement head 1000 scans the emitted irradiation light as a measurement beam using beam scanning mechanisms 1001 and 1002 and scans the measurement target 115 in two dimensions. As beam scanning mechanisms 1001 and 1002, for example, galvanometer mirrors may be used to scan the beam. By using one galvanometer mirror, it is possible to scan the measurement beam in one dimension, and by using two, it is possible to scan the measurement beam in two dimensions. In addition, other mechanisms capable of deflecting and scanning light, such as MEMS mirrors or polygon mirrors, may be used as scanning mechanisms. [Examples]

[0060] Figure 11 is a diagram showing an example of the configuration of a distance measurement system according to the sixth embodiment, and the same reference numerals are used for components identical to those in the distance measurement system 10 shown in Figure 10. In Figure 11, the distance measurement system 20 comprises a distance measurement device 100 and a measurement head 1100 connected to the distance measurement device 100 via an optical fiber 1101. The measurement head 1100 comprises a fiber focuser 112 connected to the optical fiber 1101, a rotary motor 1103, a probe shaft 1104 rotatably supported by the rotary motor 1103, and a prism 1105 attached to the tip of the probe shaft 1104.

[0061] In the distance measurement system 20, the illumination light emitted from the distance measurement device 100 is guided to the measurement head 1100 by an optical fiber 1101. The illumination light guided into the measurement head 1100 is emitted into space from the fiber focuser 112. The emitted illumination light passes through the hollow rotating motor 1103 and travels through the hollow probe shaft 1104, where it is reflected by the prism 1105 at the tip of the probe shaft. The illumination light reflected by the prism 1105 is irradiated onto the measurement target 116 and reflected by the measurement target 116. The reflected measurement light is reflected again by the prism 1105, passes through the probe shaft 1104 and the rotating motor 1103, and is focused by the fiber focuser 112. The measurement light is guided to the distance measurement device 100 via the optical fiber 1101. If the object to be measured 116 is cylindrical in shape, for example, by inserting the probe shaft 1104 into the cylinder and rotating the rotary motor 1103 in the measuring head 1100, the prism 1105 at the tip of the probe shaft 1104 rotates, making it possible to measure the cross-sectional shape inside the cylinder of the object to be measured 116. [Examples]

[0062] Figure 12 is a diagram showing an example of the configuration of a distance measurement system according to the seventh embodiment, and the same reference numerals are used for components identical to those of the distance measurement systems 10 and 20 shown in Figures 10 and 11. In Figure 12, the distance measurement system 30 includes a distance measurement device 100 and a measurement head 1200 connected to the distance measurement device 100 via an optical fiber 1101. The measurement head 1200 includes a fiber focuser 112 connected to the optical fiber 1101, λ / 4 plates 1201 and 1202 arranged on the optical path of the light emitted from the fiber focuser 112, a rotary motor 1103, a probe shaft 1104 rotatably supported by the rotary motor 1103, and a polarizing beam splitter 114 attached to the tip of the probe shaft 1104.

[0063] In the distance measurement system 30, the illumination light emitted from the distance measurement device 100 is guided to the measurement head 1200 via an optical fiber 1101 and emitted into space from the fiber focuser 112. The linearly polarized light guided from the distance measurement device 100 is converted to circular polarization by the λ / 4 plate 1201, and then becomes linearly polarized again by passing through the λ / 4 plate 1202 attached to the rotating motor 1103. The illumination light that has passed through the λ / 4 plate 1202 is reflected or transmitted by the polarizing beam splitter 114 according to the polarization direction and illuminates the measurement targets 115 and 116. At this time, by switching the polarization with the polarization switcher 111 mounted on the distance measurement device 100 and emitting the illumination light from the distance measurement device 100, the distance measurement system 30 can switch the direction of illumination of the illumination light, making it possible to perform side measurement by illuminating the measurement target 116 with illumination light and depth measurement by illuminating the measurement target 115 with illumination light.

[0064] Figure 13 shows the principle of switching the irradiation direction (measurement direction) of the irradiation light using polarization at the probe tip. The polarization beam splitter 114 at the tip of the probe shaft 1104 has the property of transmitting light vibrating parallel to the incident plane (P-polarized light) and reflecting light vibrating perpendicular to the incident plane (S-polarized light). Therefore, by electrically switching and controlling the polarization of the emitted irradiation light to P-polarized or S-polarized light with the polarization switcher 111, the measurement head 1200 can switch the irradiation direction of the irradiation light to the side irradiation direction and depth irradiation direction shown in Figure 13 using the polarization beam splitter 114.

[0065] To rotate the irradiated light while keeping it directed in the lateral illumination direction, it is necessary to rotate the polarization direction of the irradiated light L12 in accordance with the rotation of the polarizing beam splitter 114, thereby maintaining a constant relative polarization state of the irradiated light with respect to the polarizing beam splitter 114. For this purpose, two λ / 4 plates 1201 and 1202 are used. By positioning the axis of the first λ / 4 plate 1201 at a 45-degree angle to the polarization direction of the irradiated light L12, linear polarization is converted to circular polarization. The second λ / 4 plate 1202 and the polarizing beam splitter 114 are attached to a rotary motor 1103 and rotate together with the rotary motor 1103. The circularly polarized light is converted back to linear polarization when it passes through the second λ / 4 plate 1202, and as the motor rotates, a constant polarization direction is always maintained with respect to the polarizing beam splitter 114. This makes it possible to rotate the irradiated light directed in the lateral illumination direction. [Examples]

[0066] Figure 14 shows an example of the configuration of the distance measurement system according to the eighth embodiment, and the same reference numerals are used for components identical to those of the distance measurement systems 10 to 30 shown in Figures 10 to 12. In the eighth embodiment, an example configuration in which a scanning mechanism for scanning the measurement head is added to the distance measurement system shown in Figure 11 will be described.

[0067] In Figure 14, the distance measurement system 40 consists of a measuring head 1300, a Z-axis stage 1404 on which the measuring head 1300 is mounted so as to be movable in the Z-axis direction (up and down direction in the drawing), a Y-axis stage 1403 on which the object to be measured 1401 is mounted and which allows the object to be measured to be moved in the Y-axis direction (depth direction in the drawing), an X-axis stage 1402 on which the Y-axis stage 1403 is mounted and which allows the Y-axis stage and the object to be measured on the Y-axis stage to be moved in the X-axis direction (left and right direction in the drawing), a stage mechanism 1407 that supports each stage so as to be movable, a distance measuring device 100 connected to the measuring head 1300 via an optical fiber 1101, a stage controller 1406 connected to the stage mechanism 1407 via wiring 1405 and controlling the movement of each stage, a control PC 118 connected to the distance measuring device 100 and the stage controller 1406 respectively via wiring, and a display unit (display or monitor, etc.) 119 connected to the control PC 118.

[0068] The measurement head 1300 has substantially the same configuration as the measurement head 1100 shown in Figure 11, but a polarizing beam splitter 114 is attached to the tip of the probe shaft 1104.

[0069] Figure 15 shows an example of the system configuration of the distance measurement system 40. In Figure 15, the control PC includes a distance calculation unit 1501 and a shape calculation unit 1502. The operation of each component shown in Figure 15 will be specifically explained using Figure 14. In Figure 14, the irradiation light emitted from the distance measurement device 100 is guided to the measurement head 1300 by an optical fiber 1101. The irradiation light guided to the measurement head 1300 is irradiated into space by a fiber focuser, passes through a hollow rotating motor and a hollow probe shaft 1104, and is irradiated, for example, in a lateral irradiation direction by a polarizing beam splitter 114 attached to the tip.

[0070] The cylindrical object to be measured 1401 is mounted on the Y-axis stage 1403. Based on the control of the control PC 118, the stage controller 1406 drives the stage mechanism 1407 to control the movement of the X-axis stage 1402 and the Y-axis stage 1403. Following the control of the stage controller 1406, the stage mechanism 1407 moves the X-axis stage 1402 and the Y-axis stage 1403 to match the position of the probe shaft 1104, thereby adjusting the position of the object to be measured 1401. The stage controller 1406 also drives the stage mechanism 1407 to control the movement of the Z-axis stage 1404. Following the control of the stage controller 1406, the stage mechanism 1407 moves the Z-axis stage 1404, thereby inserting the probe shaft 1104 into the cavity (inside the cylinder) in the center of the object to be measured 1401.

[0071] In this state, rotating the rotary motor causes the probe shaft 1104 to rotate, which in turn causes the polarizing beam splitter 114 attached to the tip of the probe shaft to rotate. The irradiation light emitted in the lateral direction by the polarizing beam splitter 114 is irradiated onto the inner side of the cylinder of the object to be measured 1401 as it rotates. The irradiated irradiation light is reflected from the inner surface of the cylinder, and the reflected measurement light passes through the probe shaft 1104 and rotary motor again, and is focused by the fiber focuser.

[0072] The measurement light is sent to the distance measuring device 100 via the optical fiber 1101. The distance measuring device 100 calculates the distance from the probe shaft 1104 to the inner surface of the cylinder from the received measurement light. This measures the distance to the inner surface of the cylinder in one cross-section of the object to be measured 1401. Furthermore, by performing this distance measurement while moving the measurement head 1300 in the Z-axis direction (the stage controller 1406 controls the movement of the Z-axis stage 1404 by the stage mechanism 1407, thereby moving the measurement head 1300 in the Z-axis direction), it becomes possible to measure the three-dimensional shape inside the cylinder of the object to be measured 1401.

[0073] Distance measurement data from the distance measuring device 100 to the inner surface of the cylinder of the object to be measured 1401 is transmitted to the control PC 118. In addition, the position information (stage coordinates) of each stage moved by the stage mechanism 1407 is acquired by the stage controller 1406 via wiring 1405 and transmitted to the control PC 118.

[0074] In the control PC 118, distance measurement data is input to the distance calculation unit 1501, and the distance measurement result is output from the distance calculation unit 1501 to the shape calculation unit 1502. In addition, the stage coordinates and distance measurement result are input to the shape calculation unit 1502, where the measured distance value and stage coordinates are integrated to generate 3D position information. The generated 3D position information is output from the control PC 118 and displayed on the display unit 119.

[0075] In this embodiment, an example is shown in which the measurement target 1401 and the measuring head 1300 are moved using each stage. However, as another example, on-machine measurement can be achieved on a 3-axis machining center by gripping the measuring head 1300 instead of a tool. It is also possible to realize a three-dimensional shape measuring device that measures the shape of the measurement target 1401 by holding and moving the measuring head 1300 with a multi-degree-of-freedom robot. Furthermore, if the measurement target range is narrow and the shape can be measured by movement only in the Z-axis direction, the measurement target 1401 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. [Examples]

[0076] As described in the first embodiment, the FMCW distance measuring device 100 measures the distance difference between the reference light L11 branched by the optical fiber coupler 108 and the measurement light L12A reflected by the measurement target 115 or measurement target 116, up to the point where they are combined by the optical fiber coupler 109. Here, the optical path from branching by the optical fiber coupler 108 to the measurement target 115 or measurement target 116 may change in length due to changes in ambient temperature or heat, which can cause measurement errors. Therefore, it is conceivable to correct the distance origin to improve measurement accuracy. The ninth embodiment describes a distance measuring system equipped with a configuration for performing such distance origin correction.

[0077] Figure 16 is a diagram showing an example of the configuration of a distance measurement system according to the ninth embodiment, and the same reference numerals are used for components identical to those of the distance measurement systems 10 to 30 shown in Figures 10 to 12. In Figure 12, the distance measurement system 50 includes a distance measurement device 100 and a measurement head 1400 connected to the distance measurement device 100 via an optical fiber 1101. The measurement head 1400 includes a fiber focuser 112 connected to the optical fiber 1101, λ / 4 plates 1201 and 1202 arranged on the optical path of the light emitted from the fiber focuser 112, a rotary motor 1103, a probe shaft 1104 rotatably supported by the rotary motor 1103, and a polarizing beam splitter 114 attached to the tip of the probe shaft 1104.

[0078] In this embodiment, a reflective coating for distance origin generation is applied to the incident surface 1601 of the polarizing beam splitter 114. Since the material of the polarizing beam splitter is generally glass, the surface reflectivity is about 4% if there is no reflective coating. Depending on the sensitivity of the photodetector used, if the reflectivity is too strong and the photodetector becomes saturated, it is necessary to adjust the surface reflectivity to 4% or less by applying a reflective coating to the surface. In addition, reflections at the exit surfaces 1602 and 1603 of the polarizing beam splitter 114 are a source of noise and should be suppressed as much as possible. Therefore, an anti-reflective film is provided on each exit surface. A typical anti-reflective film has a reflectivity of 0.1% or less.

[0079] Figure 17 shows the FFT result of the measurement beat signal detected by the distance measurement system 50 (i.e., detected using the measurement head 1400). The measurement peak at the incident surface of the polarizing beam splitter 114, which is used as the distance origin, is defined as 1701. On the other hand, the measurement peak at the measurement target 115 when transmitted through the polarizing beam splitter, or the measurement peak at the measurement target 116 when reflected by the polarizing beam splitter, is defined as 1702. By subtracting the peak distance of measurement peak 1701 from the peak distance of measurement peak 1702, it is possible to perform distance origin correction.

[0080] Figure 18 shows an example of the processing flow for distance origin correction in the distance measuring device 100 (mainly the distance measuring control unit 117). In processing step S1800, the distance measuring device 100 determines whether to perform a side measurement or a depth measurement with respect to the target object. In the case of a side measurement, in processing step S1801, the distance measuring device 100 acquires a measurement beat signal. The distance measuring device 100 also acquires an encoder signal from the rotary motor 1103, which is synchronized with the acquisition timing of the measurement beat signal. In processing step S1802, the distance measuring device 100 calculates the distance to the target object (target distance) and the distance to the origin (origin distance). In processing step S1803, the distance measuring device 100 calculates the target distance after distance origin correction by subtracting the origin distance from the calculated target distance. Furthermore, in processing step S1804, the distance measuring device 100 calculates the diameter of the target object from the target distance after distance origin correction and the encoder signal from the rotary motor synchronized with it. It is also possible to calculate not only the diameter but also the roundness. Furthermore, the target distance after distance origin correction can be combined with the stage coordinates (measurement head scanning coordinates) described in the eighth embodiment.

[0081] On the other hand, if processing step S1800 determines that depth measurement is required, the distance measuring device 100 executes processing steps S1805 to S1807, which are the same as processing steps S1801 to S1803, and calculates the target distance (depth of the object to be measured) after distance origin correction.

[0082] The embodiments and modifications of the present invention have been described above, but the present invention is not limited to the examples of embodiments described above, and includes various modifications. For example, the examples of embodiments described above are described in detail for the purpose of making the present invention easy to understand, and the present invention is not limited to having all the configurations described herein. Furthermore, it is possible to replace a part of the configuration of one example of an embodiment with the configuration of another example. It is also possible to add a configuration of another example to the configuration of one example of an embodiment. Furthermore, it is possible to add, delete, or replace a part of the configuration of one example of each embodiment with a configuration of another example. In addition, some or all of the above configurations, functions, processing units, processing means, etc., may be realized in hardware, for example, by designing them as integrated circuits. Also, the control lines and information lines in the figures are shown only if they are considered necessary for explanation, and do not necessarily show all of them. It can be assumed that almost all of the configurations are interconnected. [Explanation of Symbols]

[0083] 10, 20, 30, 40, 50: Distance measurement system 100, 200, 300: Distance measuring device 101: Laser light source 102: Oscillator 103, 104, 106, 108, 109: Fiber optic couplers 105, 1101: Optical fiber 107, 113: Receiver 110: Polarizing Beam Combiner 111: Polarization switch 112: Fiber Focuser 114: Polarizing Beam Splitter 115, 116, 1401: Measurement target 117: Distance Measurement Control Unit 118: Control PC 119: Display section 601, 602, 701: Polarizer 801: Insulated Box 802: Temperature sensor 901: Faraday Roteta 902:λ / 2 plate 903: Rotation mechanism 1000, 1100, 1200, 1300, 1400: Measuring head 1001, 1002: Beam scanning mechanism 1100: Measuring head 1103: Rotary motor 1104: Probe shaft 1105: Prism 1201, 1202: λ / 4 plate 1402: X-axis stage 1403: Y-axis stage 1404: Z-axis stage 1405: Wiring 1406: Stage Controller 1407: Stage mechanism 1501: Distance calculation section 1502: Shape calculation section

Claims

1. A distance measuring device for measuring the distance to an object to be measured, A laser light source, A measurement optical system that detects a measurement beat signal by passing the irradiation light generated by the laser light source through it and passing the measurement light reflected by the object to be measured through it, The system includes a measuring unit that measures the distance from the measurement beat signal to the object to be measured, The aforementioned measuring optical system is A polarization separation unit separates two orthogonal polarization components in light and outputs them to different optical paths, It includes a polarization switching unit that changes the polarization direction of light, When the irradiated light passes through the measuring optical system, the polarization separation unit allows the irradiated light to pass through, and the polarization switching unit changes the polarization direction of the irradiated light that has passed through the polarization separation unit by a predetermined angle. When the measurement light passes through the measurement optical system, the polarization switching unit changes the polarization direction of the measurement light by a predetermined angle, and the polarization separation unit separates the two orthogonal polarization components of the measurement light whose polarization direction has been changed by the polarization switching unit. Distance measuring device.

2. A distance measuring device according to claim 1, The predetermined angle is 45 degrees. The polarization switching unit changes the polarization direction of the irradiated light by 45 degrees, and further changes the polarization direction of the measurement light by 45 degrees, thereby making the polarization direction of the measurement light perpendicular to the polarization direction of the irradiated light. Distance measuring device.

3. A distance measuring device according to claim 1, The polarization switching unit is a polarization switcher that rotates the polarization direction of incident light according to the applied voltage. Distance measuring device.

4. A distance measuring device according to claim 1, The polarization switching unit comprises a Faraday rotator and a λ / 2 plate, and by changing the polarization directions of the irradiated light and the measured light respectively, the polarization direction of the measured light is made perpendicular to the polarization direction of the irradiated light. Distance measuring device.

5. A distance measuring device according to claim 1, The two orthogonal polarization components are the principal component and the leaked light component. The measurement optical system detects the measurement beat signal using the measurement light from which the stray light component has been separated by the polarization separation unit. Distance measuring device.

6. A distance measuring device according to claim 5, The measurement optical system further includes a reference light branching unit that branches the light generated by the laser light source into the irradiation light and the reference light, The measurement beat signal is detected by interfering the measurement light, from which the leaked light component has been separated, with the reference light. Distance measuring device.

7. A distance measuring device according to claim 5, The measurement optical system further includes an orthogonal polarization component attenuation element that transmits the main component of the measurement light from which the leaked light component has been separated, and attenuates the leaked light component. Distance measuring device.

8. A distance measuring device according to claim 6, The measurement optical system further comprises an orthogonal polarization component attenuation element that transmits the main component of the reference light and attenuates the stray light component. Distance measuring device.

9. A distance measuring device according to claim 1, A first branching unit that splits the light generated by the laser light source into a first beam and a second beam, A second branching section that branches the irradiation light from the second light, A reference optical system that detects a reference beat signal by passing the first light through it, Furthermore, The two orthogonal polarization components are the principal component and the leaked light component. The reference optical system further comprises orthogonal polarization component attenuation elements that transmit the main component of the first light and attenuate the stray light component. Distance measuring device.

10. A distance measuring device according to claim 9, The reference optical system further comprises an insulating box covering at least a portion thereof. Distance measuring device.

11. A distance measuring system comprising at least a distance measuring device and a measuring head that irradiates a target to be measured with light emitted from the distance measuring device, wherein the distance to the target to be measured is measured using the measuring light reflected from the target, The distance measuring device is, A laser light source, A measuring optical system that detects a measurement beat signal by passing the irradiation light generated by the laser light source through and the measurement light through, The system includes a measuring unit that measures the distance from the measurement beat signal to the object to be measured, The aforementioned measuring optical system is A polarization separation unit separates two orthogonal polarization components in light and outputs them to different optical paths, It includes a polarization switching unit that changes the polarization direction of light, When the irradiated light passes through the measuring optical system, the polarization separation unit allows the irradiated light to pass through, and the polarization switching unit changes the polarization direction of the irradiated light that has passed through the polarization separation unit by a predetermined angle. When the measurement light passes through the measurement optical system, the polarization switching unit changes the polarization direction of the measurement light by a predetermined angle, and the polarization separation unit separates the two orthogonal polarization components of the measurement light whose polarization direction has been changed by the polarization switching unit. Distance measurement system.

12. A distance measuring system according to claim 11, The two orthogonal polarization components are the principal component and the leaked light component. The measurement optical system detects the measurement beat signal using the measurement light from which the stray light component has been separated by the polarization separation unit. Distance measurement system.

13. A distance measurement system according to claim 12, The measurement optical system further includes an orthogonal polarization component attenuation element that transmits the main component of the measurement light from which the leaked light component has been separated, and attenuates the leaked light component. Distance measurement system.

14. A distance measuring device comprising a laser light source, a measuring optical system, and a measuring unit, wherein the measuring optical system comprises a polarization separation unit that separates two orthogonal polarization components in light and outputs them to different optical paths, and a polarization switching unit that changes the polarization direction of light, and a distance measuring device for measuring the distance to a measurement target, In the aforementioned measuring optical system, As the irradiation light generated by the laser light source passes through, the polarization separation unit allows the irradiation light to pass through, and the polarization switching unit changes the polarization direction of the irradiation light that has passed through the polarization separation unit by a predetermined angle. When the measurement light reflected by the object to be measured passes through the aforementioned irradiation light, the polarization switching unit changes the polarization direction of the measurement light by a predetermined angle, and the polarization separation unit separates the two orthogonal polarization components of the measurement light whose polarization direction has been changed by the polarization switching unit. The measurement beat signal is detected by the aforementioned measurement light. The measurement unit measures the distance from the measurement beat signal to the object to be measured. Distance measurement method.

15. A distance measurement method according to claim 14, The two orthogonal polarization components are the principal component and the leaked light component. In the measurement optical system, the measurement beat signal is detected using the measurement light from which the stray light component has been separated by the polarization separation unit. Distance measurement method.

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