Wavelength dispersion compensation device, optical distance measurement device, and wavelength dispersion compensation method

Abstract

A wavelength dispersion compensation device (6) comprises: a wavelength dispersion compensation unit (61) that, on the basis of a set wavelength dispersion compensation amount, compensates for the difference in wavelength dispersion of a reference interference signal with respect to a measurement interference signal; and a wavelength dispersion amount adjustment unit (62) that, on the basis of a compensation index corresponding to the difference in wavelength dispersion between the reference interference signal and the measurement interference signal, adjusts the wavelength dispersion compensation amount set in the wavelength dispersion compensation unit 61.

Description

Wavelength dispersion compensation device, optical distance measuring device, and wavelength dispersion compensation method

[0001] The present disclosure relates to a chromatic dispersion compensation device, an optical distance measuring device, and a chromatic dispersion compensation method.

[0002] There is an optical ranging method for measuring the distance to an object based on the peak position in the spectrum of a measurement interference signal obtained from an optical signal that does not pass through the object and an optical signal that passes through the object. For example, Patent Document 1 describes an optical tomographic imaging method for generating a tomographic image based on the depth direction distance of the object. This method splits light emitted from a light source unit into a measurement light and a reference light, irradiates the measurement light onto a biological object, combines the reflected light from the object with the reference light, detects interference light between the combined reflected light and the reference light, and obtains a tomographic image of the object from the detected interference light. In the optical ranging method, if the measurement interference signal changes nonlinearly with time, the shape of the spectrum obtained by Fourier transforming the measurement interference signal broadens, reducing the accuracy of distance measurement based on the peak position.

[0003] In response to this, an optical distance measuring device equipped with a reference interferometer and a measurement interferometer has been proposed. The reference interferometer generates a reference interference signal by combining wavelength-swept light that has passed through two optical paths with different optical path lengths. The measurement interferometer generates a measurement interference signal by combining wavelength-swept light that has passed through an optical path that passes through an object and an optical path that does not pass through the object. By inputting the same wavelength-swept light into the reference interferometer and the measurement interferometer, the reference interferometer signal and the measurement interferometer signal exhibit the same nonlinear time change. This makes it possible to compensate for the nonlinearity of the measurement interferometer signal using the reference interferometer signal.

[0004] Japanese Patent Application Laid-Open No. 2007-267927

[0005] However, in conventional optical distance measuring devices, the reference interferometer system is a path that does not pass through the target object and is composed of optical fiber, while the measurement interferometer system is a path that passes through the target object via an air layer. This means that there is a possibility that the reference interferometer signal and the measurement interferometer signal will have different chromatic dispersion, which is the dependence of the refractive index on the wavelength. In this case, distortion occurs in the frequency spectrum obtained from these signals, which reduces the accuracy of distance measurement based on the peak position.

[0006] The present disclosure is intended to solve the above-mentioned problems, and has an object to provide a chromatic dispersion compensation device that can reduce the effect on measurement accuracy caused by the difference in chromatic dispersion between a reference interference signal and a measurement interference signal.

[0007] A wavelength dispersion compensation device according to the present disclosure is a wavelength dispersion compensation device that compensates for the difference in wavelength dispersion between a reference interference signal and a measurement interference signal in an optical distance measuring device that includes: a wavelength swept light source that outputs wavelength swept light; a reference interferometer that has two optical paths with different optical path lengths and generates a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; and a measurement interferometer that has an optical path that passes through an object and an optical path that does not pass through the object and generates the measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths. The wavelength dispersion compensation device comprises: a compensator that compensates for the difference in wavelength dispersion between the reference interference signal and the measurement interference signal based on a set amount of wavelength dispersion compensation; and an adjuster that adjusts the amount of wavelength dispersion compensation to be set in the compensator based on a compensation index corresponding to the difference in wavelength dispersion between the reference interference signal and the measurement interference signal.

[0008] According to the present disclosure, the amount of chromatic dispersion compensation is adjusted based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal, and the difference in chromatic dispersion between the reference interference signal and the measurement interference signal is compensated for based on the adjusted amount of chromatic dispersion compensation. This allows the chromatic dispersion compensation device according to the present disclosure to reduce the impact on measurement accuracy caused by the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0009] 1A and 1B are diagrams showing reflected light, reference light, a beat signal, and a frequency spectrum of wavelength swept light. FIG. 1A is a diagram showing an overview of chromatic dispersion compensation using a reference interference signal. FIG. 1B is a block diagram showing the configuration of an optical distance measuring device according to a first embodiment. FIG. 1C is a flowchart showing the operation of the optical distance measuring device according to the first embodiment. FIG. 1D is a flowchart showing the calculation process of a compensation index. FIG. 1E is a flowchart showing a chromatic dispersion compensation method according to the first embodiment. FIG. 1F is a diagram showing an overview of chromatic dispersion compensation processing in the first embodiment. FIG. 1G is a block diagram showing the configuration of a modified example of the optical distance measuring device according to the first embodiment. FIG. 1H is a block diagram showing a hardware configuration that realizes the functions of the chromatic dispersion compensation device according to the first embodiment.

[0010] Embodiment 1 An optical distance measuring device according to embodiment 1 measures the distance to an object using a measurement interference signal generated by a measurement interferometry system. The optical distance measuring device according to embodiment 1 also uses a reference interference signal generated by a reference interferometry system to compensate for nonlinear changes (nonlinearity) over time in the measurement interference signal.

[0011] 1A is a diagram showing reflected light A1, reference light B1, beat signal AB1, and spectrum C1, whose wavelength sweep changes linearly with time. The upper diagram in FIG. 1A shows the time changes of reflected light A1 and reference light B1. As shown in this diagram, the wavelength sweep of reflected light A1 and reference light B1 is linear with time. Reflected light A1 is wavelength swept light irradiated onto an object from an optical distance measuring device and reflected by the object. Reference light B1 is a reference for the wavelength change of reflected light A1 with time, and like reflected light A1, changes linearly with time.

[0012] Beat signal AB1 is a signal obtained by combining reflected light A1 and reference light B1 and causing them to interfere with each other. The beat frequency fb of beat signal AB1 is proportional to the wavelength difference between reflected light A1 and reference light B1. The middle diagram in FIG. 1A shows the time variation of beat signal AB1. As shown in this diagram, when the wavelength sweeps of reflected light A1 and reference light B1 are linear with respect to time, beat signal AB1 remains constant.

[0013] By performing a Fourier transform (FT) on the beat signal AB1, the frequency spectrum C1 shown in the lower part of FIG. 1A is obtained. The frequency spectrum C1 is proportional to the position of the object. The frequency corresponding to the peak position of the frequency spectrum C1 represents the distance to the object. The optical distance measuring device calibrates the relationship between the frequency of the beat signal AB1 and the distance in advance, and calculates the distance using this relationship.

[0014] 1B shows reflected light A2, reference light B2, beat signal AB2, and frequency spectrum C2, whose wavelength sweep changes nonlinearly with time. The upper diagram in FIG. 1B shows the time changes of reflected light A2 and reference light B2. As shown in this diagram, the wavelength sweep of reflected light A2 and reference light B2 is nonlinear with time. Reflected light A2 is wavelength swept light irradiated onto an object from an optical distance measuring device and reflected by the object. Reference light B2 is a reference for the wavelength change of reflected light A2 with time, and changes nonlinearly with time, second-order or higher.

[0015] Beat signal AB2 is a signal obtained by combining reflected light A2 and reference light B2 and causing them to interfere with each other. The beat frequency fb of beat signal AB2 is proportional to the wavelength difference between reflected light A2 and reference light B2. The middle diagram in FIG. 1B shows the time variation of beat signal AB2. As this diagram shows, the wavelength sweeps of reflected light A2 and reference light B2 are nonlinear with respect to time, so beat signal AB2 is not constant with respect to time.

[0016] By performing a Fourier transform (FT) on the beat signal AB2, the frequency spectrum C2 shown in the lower part of Fig. 1B is obtained. The frequency spectrum C2 is distorted as shown in the lower part of Fig. 1B, and the peak position cannot be accurately extracted. Although the optical distance measuring device calibrates the relationship between the frequency of the beat signal AB2 and the distance in advance, the peak position cannot be accurately extracted, and therefore the distance cannot be accurately calculated using this relationship.

[0017] In contrast, the optical distance measuring device according to the first embodiment compensates for the wavelength sweep nonlinearity in the measurement interference signal corresponding to beat signal AB2 shown in Fig. 1B by using a reference interference signal having the same wavelength sweep nonlinearity as the measurement interference signal. This eliminates distortion in the spectrum obtained by Fourier transforming the measurement interference signal, making it possible to accurately measure the distance to the target object based on the peak position of the spectrum.

[0018] Fig. 2 is a diagram showing an overview of chromatic dispersion compensation using a reference interference signal. In Fig. 2, the upper left diagram shows a time variation of the reference interference signal D, the middle left diagram shows a time variation of the measurement interference signal E, and the lower left diagram shows a waveform F of the measurement interference signal resampled based on the reference interference signal D. The waveform F of the measurement interference signal is obtained by so-called resampling, which involves sampling the measurement interference signal E at the zero-crossing points of the rising edge of the reference interference signal D, as shown in Fig. 2.

[0019] 2, the upper right diagram is waveform G showing the time change of the beat frequency fb of the reference interference signal D. The beat frequency fb of the reference interference signal D is proportional to the optical path length difference in the reference interferometer. The middle right diagram is waveform H showing the time change of the beat frequency fb of the measurement interference signal E. The lower right diagram is waveform I showing the relationship between wave number and distance obtained based on the measurement interference signal F.

[0020] Waveforms G and H are calculated based on the reference interference signal D and the measured interference signal E, which have the same nonlinear change with time during the wavelength sweep. Therefore, waveforms G and H have similar nonlinearities. As a result, waveform I becomes a waveform in which the distance is approximately constant with respect to the wavenumber. By Fourier transforming this waveform I, spectrum J is obtained. In spectrum J, a reflection peak appears at a frequency position corresponding to the distance from the reflection point of the object. For example, if an object is placed at a distance L from the interference origin, a reflection peak from the object appears at a frequency position corresponding to the distance L.

[0021] However, as will be described later with reference to Fig. 3, the reference interferometry system uses a path that does not pass through the target, whereas the measurement interferometry system uses a path that passes through the target via an air layer. In this case, differences in chromatic dispersion occur between the reference interferometry signal and the measurement interferometry signal, resulting in slight distortion in waveform I and in spectrum J, as shown in Fig. 2. This reduces the accuracy of distance measurement based on the peak position of spectrum J.

[0022] (Basic Configuration of Optical Distance Measuring Device) Therefore, the optical distance measuring device according to the first embodiment adjusts the amount of chromatic dispersion compensation based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal, and compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the adjusted amount of chromatic dispersion compensation. Fig. 3 is a block diagram showing the configuration of the optical distance measuring device 1 according to the first embodiment. As shown in Fig. 3, the optical distance measuring device 1 includes a wavelength swept light source 2, a reference interferometer system 3, a measurement interferometer system 4, a signal processing unit 5, a chromatic dispersion compensator 6, an optical coupler 7, and a lens barrel 8, and measures the distance to the target TG.

[0023] (Wavelength Swept Light Source) The wavelength swept light source 2 outputs wavelength swept light based on a sweep signal. The wavelength swept light source 2 includes an electrical unit 21 and a light source 22. The electrical unit 21 generates a potential sweep signal and outputs the generated sweep signal to the light source 22. The light source 22 generates wavelength swept light whose wavelength changes in synchronization with the potential of the sweep signal and outputs the wavelength swept light. The wavelength swept light output from the wavelength swept light source 2 is output to an optical coupler 7 via an optical fiber. The optical coupler 7 branches the wavelength swept light to a reference interferometer 3 and a measurement interferometer 4 via an optical fiber.

[0024] (Reference Interferometry System) The reference interferometry system 3 has two optical paths with different optical path lengths, and generates a reference interference signal by photoelectrically converting reference interference light obtained by combining wavelength-swept light that has passed through the two optical paths. For example, as shown in Fig. 3, the reference interferometry system 3 is connected to an optical coupler 31, an optical coupler 32, an opto-electric converter 33, and an AD converter 34 via optical fibers. Two optical paths formed by optical fibers are connected to the optical coupler 31, and these optical paths have different optical path lengths.

[0025] The optical coupler 31 receives the wavelength swept light from the wavelength swept light source 2 via the optical coupler 7, and splits the received wavelength swept light into two optical paths. The two optical paths are configured with optical fibers. The chromatic dispersion compensator 61 is provided in the optical fiber of one of the two optical paths. The optical coupler 32 outputs the wavelength swept light that has passed through the two optical paths to the photoelectric converter 33.

[0026] The photoelectric conversion unit 33 multiplexes the input wavelength swept light and photoelectrically converts the multiplexed light to generate an electrical reference interference signal. The AD conversion unit 34 analog-to-digital converts the electrical reference interference signal generated by the photoelectric conversion unit 33 to generate a digital reference interference signal. The digital reference interference signal converted by the AD conversion unit 34 is output to the signal processing unit 5.

[0027] (Measurement Interferometry System) The measurement interferometry system 4 has an optical path that passes through the object TG and an optical path that does not pass through the object TG, and generates a measurement interferometry signal by photoelectrically converting measurement interferometry light obtained by combining wavelength-swept light that has passed through the two optical paths. For example, as shown in Fig. 3, the measurement interferometry system 4 is connected to an optical coupler 41, a circulator 42, an optical coupler 43, a photoelectric conversion unit 44, and an AD conversion unit 45 via optical fibers. Two optical paths formed by optical fibers are connected to the optical coupler 41.

[0028] The optical coupler 41 receives the wavelength swept light from the wavelength swept light source 2 via the optical coupler 7, and splits the received wavelength swept light into two optical paths. The two optical paths are composed of optical fibers. The circulator 42 is provided in the optical fiber of one of the two optical paths. The circulator 42 outputs the wavelength swept light from the optical coupler 41 to the optical tube 8, and outputs the light returning from the optical tube 8 to the optical coupler 43.

[0029] The lens barrel 8 is an optical system that irradiates the light output from the circulator 42 onto the target TG through an air layer and returns the reflected light, which is the irradiated light reflected by the target TG through the air layer, to the circulator 42. The optical coupler 43 outputs to the photoelectric conversion unit 44 the wavelength swept light that has passed through an optical path that passes through the target TG by the lens barrel 8 and the wavelength swept light that has passed through an optical path that does not pass through the target TG.

[0030] The photoelectric conversion unit 44 multiplexes the input wavelength swept light and photoelectrically converts the multiplexed light to generate an electrical measurement interference signal. The AD conversion unit 45 performs analog-to-digital conversion on the electrical measurement interference signal generated by the photoelectric conversion unit 44 to generate a digital measurement interference signal. The measurement interference signal converted into a digital signal by the AD conversion unit 45 is output to the signal processing unit 5.

[0031] The signal processing unit 5 resamples the measurement interference signal based on the reference interference signal, performs a Fourier transform on the resampled measurement interference signal, and measures the distance to the target TG based on the optical path length difference of the measurement interferometry system calculated based on the peak position of the spectrum obtained by the Fourier transform. The signal processing unit 5 also calculates a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the phase difference between the two. As shown in FIG. 3 , the signal processing unit 5 includes a resampling unit 51, a Fourier transform unit 52 (hereinafter referred to as FFT unit 52), a distance measurement unit 53, and a feedback unit 54 (hereinafter referred to as FB unit 54).

[0032] (Resampling Unit) The resampling unit 51 receives the reference interference signal from the reference interference system 3 and the measurement interference signal from the measurement interferometry system 4, and resamples the measurement interference signal based on the reference interference signal. For example, the resampling unit 51 samples the measurement interference signal using the reference interference signal as a clock signal. For example, the resampling unit 51 may sequentially sample the measurement interference signal at the time points where the rising edge of the reference interference signal crosses zero. The measurement interference signal sampled by the resampling unit 51 is output to the FFT unit 52.

[0033] (FFT Unit) The FFT unit 52 performs a Fourier transform on the measurement interference signal resampled by the resampling unit 51. For example, the FFT unit 52 performs a fast Fourier transform on the measurement interference signal to obtain a spectrum. In this spectrum, a reflection peak appears at a frequency position corresponding to the distance from the reflection point on the target TG.

[0034] (Distance Measuring Unit) The distance measuring unit 53 calculates the optical path length difference in the measurement interferometry system 4 based on the peak position of the spectrum obtained by Fourier transform, and measures the distance to the target TG based on the calculated optical path length difference. Peaks corresponding to wave numbers appear in the spectrum, and the peak positions correspond to the optical path length difference in the measurement interferometry system 4. The distance measuring unit 53 converts the optical path length difference in the measurement interferometry system 4 into distance based on the relationship between the speed of light and the wave number.

[0035] (FB Unit) The FB unit 54 calculates a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal, based on the phase difference between them. This allows the chromatic dispersion compensation device 6 to obtain a compensation index for compensating for the difference in chromatic dispersion between the reference interferometer 3 and the measurement interferometer 4. The FB unit 54 calculates the compensation index for chromatic dispersion based on the signals obtained by the reference interferometer 3 and the measurement interferometer 4, and feeds back the calculated compensation index to the chromatic dispersion compensation device 6. As shown in FIG. 3 , the FB unit 54 includes a Hilbert transform unit 541, an unwrap unit 542, and a difference acquisition unit 543.

[0036] The Hilbert transformer 541 performs a Hilbert transform on the reference interference signal and the measurement interference signal. The Hilbert transform is a method for converting a time-domain signal into a frequency-domain signal. The Hilbert transform generates an analytic signal consisting of the real and imaginary parts of the original signal. This analytic signal has the same amplitude as the original signal and contains information about its phase.

[0037] The unwrapping unit 542 unwraps the Hilbert-transformed reference interference signal and the measurement interference signal. For example, the phase information of the Hilbert-transformed signal is expressed in the range of −π to π. Phase unwrapping is a process of detecting discontinuous jumps in phase and continuously connecting them to an accurately estimated phase. This ensures phase continuity. For example, the unwrapping unit 542 detects 2π jumps and corrects them to a continuous phase, or calculates the phase difference and continuously integrates it to estimate the phase.

[0038] The difference acquisition unit 543 calculates a chromatic dispersion correction term as a compensation index based on the phase difference between the unwrapped reference interference signal and the measurement interference signal. The chromatic dispersion correction term may be, for example, a phase difference corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal. The correction term calculated by the difference acquisition unit 543 is fed back from the signal processing unit 5 to the chromatic dispersion amount adjustment unit 62.

[0039] (Chromatic Dispersion Compensation Device) The chromatic dispersion compensation device 6 is a device that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal in the optical distance measuring device 1. As shown in Fig. 3, the chromatic dispersion compensation device 6 includes a chromatic dispersion compensation unit 61 and a chromatic dispersion amount adjustment unit 62.

[0040] (Wavelength dispersion compensator) The wave length dispersion compensator 61 is a compensator that compensates for the difference in wavelength dispersion between the reference interference signal and the measurement interference signal based on a set amount of wavelength dispersion compensation. For example, the wave length dispersion compensator 61 is configured to include a wavelength dispersion member having the same or similar amount of wavelength dispersion as the measurement interferometer. By including the wavelength dispersion member, the wave length dispersion compensator 61 can compensate for the difference in wavelength dispersion between the reference interference signal and the measurement interference signal.

[0041] The chromatic dispersion component is a component used to compensate for or control chromatic dispersion. Examples of the chromatic dispersion component include a holey fiber, a dispersion fiber, a dispersion compensation module, and a dispersion compensation film. By using a holey fiber or a dispersion fiber, the chromatic dispersion compensator 61 can compensate for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0042] A holey fiber is a special optical fiber with a periodic structure that can control chromatic dispersion. For example, holey fiber can adjust the propagation characteristics of the optical fiber and compensate for dispersion in a specific wavelength range. A dispersive fiber is an optical fiber designed to compensate for chromatic dispersion in a specific wavelength range. The refractive index profile of the dispersive fiber is designed to offset the dispersion characteristics at a specific wavelength. A dispersion compensation module is an example of a chromatic dispersion compensation device that includes a dispersive fiber. For example, a dispersion compensation module includes optical elements or piping connected via a dispersive fiber to compensate for differences in chromatic dispersion. A dispersion compensation film is a chromatic dispersion component provided in the form of an optical film. For example, a dispersion compensation film is used to compensate for chromatic dispersion in a specific wavelength range and is applied to the surface of an optical element or device.

[0043] The chromatic dispersion compensator 61 minimizes the effects of chromatic dispersion by controlling the temperature of the optical fiber that constitutes the optical path of the reference interferometer 3 using, for example, a temperature control device and applying a set amount of chromatic dispersion. For example, the characteristics of holey fiber or dispersive fiber are affected by changes in temperature. In particular, the refractive index or dispersion characteristics of optical fiber tend to change with temperature. Generally, as the temperature of an optical fiber increases, its refractive index decreases and the chromatic dispersion characteristics change. For example, the chromatic dispersion compensator 61 maintains a constant temperature of the optical fiber using a temperature control device that controls the temperature of the optical fiber of the reference interferometer 3, thereby eliminating the difference in chromatic dispersion between the reference interferometer 3 and the measurement interferometer 4.

[0044] The chromatic dispersion compensating unit 61 may also use pressure to compensate for the difference in chromatic dispersion between the reference interferometer 3 and the measurement interferometer 4. The refractive index or propagation speed of an optical fiber or optical element may change depending on the pressure. This change can be utilized to compensate for the difference in chromatic dispersion. For example, the chromatic dispersion compensating unit 61 uses a pressure control device that applies pressure to the optical fiber or optical element. The chromatic dispersion compensating unit 61 uses the pressure control device to apply pressure to the optical fiber or optical element of the reference interferometer 3, thereby changing the refractive index of the optical fiber or optical element and changing the chromatic dispersion characteristics. Due to this change, the chromatic dispersion compensating unit 61 corrects the difference in chromatic dispersion between the reference interferometer 3 and the measurement interferometer 4.

[0045] In addition, the chromatic dispersion compensation unit 61 can be used to correct differences in chromatic dispersion, even if the physical quantity is other than temperature and pressure, as long as the physical quantity is capable of changing the chromatic dispersion characteristics of the optical path of the reference interferometer 3.

[0046] (Chromatic Dispersion Adjustment Unit) The chromatic dispersion adjustment unit 62 is an adjustment unit that adjusts the amount of chromatic dispersion compensation to be set in the chromatic dispersion compensation unit 61 based on the compensation index acquired from the FB unit 54. For example, the amount of chromatic dispersion compensation is calculated based on a phase difference corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal. The chromatic dispersion adjustment unit 62 calculates the amount of chromatic dispersion compensation using preset calibration data or a calibration model related to the temperature dependency of the optical fiber. The chromatic dispersion adjustment unit 62 adjusts the amount of chromatic dispersion compensation as the temperature of the optical fiber in the reference interferometer 3 changes, to correspond to the temperature dependency.

[0047] The influence of the difference in chromatic dispersion between the reference interference signal and the measurement interference signal is determined by the length of the air layer between the reference interference signal and the target object TG. The length of the air layer also changes due to temperature changes in the lens barrel 8, i.e., changes in the amount of expansion and contraction of the lens barrel 8 caused by temperature changes. However, while a typical measurement cycle is approximately 1,000 times per second, the temperature change rate of the lens barrel 8 is estimated to be approximately 0.1 degrees per second. Therefore, the chromatic dispersion amount adjuster 62 may periodically acquire the compensation index and adjust the chromatic dispersion compensation amount set in the chromatic dispersion compensator 61 based on the acquired compensation index. For example, the compensation index may be acquired during a periodic calibration process of the optical distance measuring device 1. This allows the chromatic dispersion compensator 6 to perform chromatic dispersion compensation using simple signal processing to acquire the compensation index without frequently acquiring the compensation index.

[0048] Next, the operation of the optical distance measuring device 1 according to the first embodiment will be described. Fig. 4 is a flowchart showing the operation of the optical distance measuring device 1 according to the first embodiment. The wavelength swept light output from the wavelength swept light source 2 is branched to the reference interferometer 3 and the measurement interferometer 4. The reference interferometer 3 generates a reference interference signal from the wavelength swept light, and the measurement interferometer 4 generates a measurement interference signal from the wavelength swept light (step ST1). The reference interference signal and the measurement interference signal are output to the signal processor 5.

[0049] Next, in the signal processing unit 5, the feedback unit 54 calculates a correction term for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the phase difference between the two, and feeds back the calculated correction term to the chromatic dispersion amount adjusting unit 62 (step ST2). The chromatic dispersion compensating device 6 compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the correction term fed back from the feedback unit 54 (step ST3). As a result, the reference interference system 3 and the measurement interferometry system 4 generate a reference interference signal and a measurement interference signal in which the difference in chromatic dispersion has been compensated for. The reference interference signal and the measurement interference signal are output to the signal processing unit 5.

[0050] The resampling unit 51 resamples the measurement interference signal based on the reference interference signal and outputs the resampled measurement interference signal to the FFT unit 52 (step ST4). The FFT unit 52 performs a Fourier transform on the resampled measurement interference signal (step ST5). The spectrum obtained by the Fourier transform is output from the FFT unit 52 to the distance measuring unit 53. The distance measuring unit 53 calculates the optical path length difference of the measurement interferometry system based on the peak position of the spectrum generated by the FFT unit 52, and measures the distance to the target TG based on the calculated optical path length difference of the measurement interferometry system (step ST6).

[0051] 5 is a flowchart showing the process of calculating the compensation index, illustrating the operation of the FFT unit 52. The Hilbert transform unit 541 performs Hilbert transform on the reference interference signal and the measurement interference signal (step ST1A). The signals obtained by performing Hilbert transform on the reference interference signal and the measurement interference signal are output to the unwrap unit 542.

[0052] The unwrapping unit 542 unwraps the Hilbert-transformed reference interference signal and the measurement interference signal (step ST2A). For example, the unwrapping unit 542 unwraps the Hilbert-transformed reference interference signal to generate a signal indicating the phase change over time of the reference interference signal, and unwraps the Hilbert-transformed measurement interference signal to generate a signal indicating the phase change over time of the measurement interference signal. The measurement interferometer 4 has an optical path length difference determined by the optical path formed by optical fiber between it and the reference interferometer 3. Therefore, the peak height of the waveform of the signal indicating the phase change over time of the measurement interference signal is lower than that of the reference interference signal. Therefore, the unwrapping unit 542 doubles the signal indicating the phase change over time of the measurement interference signal by a ratio corresponding to the optical path length difference between the two interferometers.

[0053] The difference acquiring unit 543 calculates a phase difference corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal as a correction term for correcting the difference in chromatic dispersion based on the phase difference between the unwrapped reference interference signal and the measurement interference signal (step ST3A). For example, the difference acquiring unit 543 calculates the difference between the signal indicating the phase change over time of the reference interference signal generated by the unwrapping unit 542 and the signal indicating the phase change over time of the measurement interference signal, multiplied by a ratio corresponding to the difference in optical path length between both interferometers, as the phase difference corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal. The correction term calculated by the difference acquiring unit 543 is fed back from the signal processing unit 5 to the chromatic dispersion amount adjusting unit 62.

[0054] Next, the operation of the chromatic dispersion compensation device 6 according to the first embodiment will be described. FIG. 6 is a flowchart showing a chromatic dispersion compensation method according to the first embodiment. The chromatic dispersion adjustment unit 62 adjusts the amount of chromatic dispersion compensation set in the chromatic dispersion compensation unit 61 based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal (step ST1B). Next, the chromatic dispersion compensation unit 61 compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the amount of chromatic dispersion compensation set by the chromatic dispersion adjustment unit 62 (step ST2B). By having the chromatic dispersion compensation device 6 perform the above method, it is possible to reduce the impact on measurement accuracy caused by the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0055] (Overview of Chromatic Dispersion Compensation) FIG. 7 is a diagram illustrating an overview of chromatic dispersion compensation processing in the first embodiment. The diagram enclosed by a dashed line on the left side of FIG. 7 illustrates an overview of processing by the FB unit 54, while the diagram illustrating a series of processing on the right side illustrates processing by components other than the FB unit 54 of the signal processing unit 5. The Hilbert transformer 541 performs Hilbert transform on the reference interference signal D and the measurement interference signal E. The unwrapping unit 542 unwraps the Hilbert transformed reference interference signal D and measurement interference signal E, respectively, to generate a signal G indicating a change in phase Φ over time for the reference interference signal D and a signal H indicating a change in phase Φ over time for the measurement interference signal E. As shown in FIG. 7 , the peak height in the waveform of signal H is lower than that of signal G. Therefore, the unwrapping unit 542 generates a signal K by doubling the waveform of signal H at a ratio corresponding to the optical path length difference between the reference interferometer 3 and the measurement interferometer 4.

[0056] The difference acquisition unit 543 calculates the difference L between the waveform of the signal G and the waveform of the signal K as a phase difference corresponding to the difference in chromatic dispersion between the reference interference signal D and the measurement interference signal E. The phase difference is calculated by subtracting the correction term Ae －ｉΔφ（ｔ） A is the amplitude of the waveform L, and Δφ(t) is the phase difference at time t. The correction term Ae calculated by the difference acquisition unit 543 －ｉΔφ（ｔ） is fed back to the chromatic dispersion amount adjusting unit 62 .

[0057] The chromatic dispersion amount adjusting unit 62 is set in advance with a relationship of correction terms according to the temperature T at a certain time t, as shown in the upper right part of Fig. 7. For example, during measurement, the chromatic dispersion amount adjusting unit 62 adjusts the phase difference A ｄｉｓ When e−iΔφdis(t, T) is obtained, the amount of chromatic dispersion compensation is adjusted using a preset relationship of the correction term according to the temperature T.

[0058] Once the difference in chromatic dispersion between the reference interference signal D and the measurement interference signal E has been compensated for, the resampling unit 51 resamples the measurement interference signal E based on the reference interference signal D and outputs the resampled measurement interference signal to the FFT unit 52 (step ST4). The FFT unit 52 performs a Fourier transform on the resampled measurement interference signal I to obtain a spectrum J. The distance measuring unit 53 calculates the optical path length difference between the reference interferometer 3 and the measurement interferometer 4 based on the peak position of the spectrum J generated by the FFT unit 52, and measures the distance to the target TG based on the calculated optical path length difference.

[0059] (Modification) FIG. 8 is a block diagram showing the configuration of a chromatic dispersion compensation device 6A, which is a modification of the chromatic dispersion compensation device 6. In FIG. 8, the chromatic dispersion compensation device 6A compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal in the optical distance measuring device 1. As shown in FIG. 8, the chromatic dispersion compensation device 6A includes a Hilbert transformer 611, an unwrapping unit 612, a difference acquisition unit 613, a chromatic dispersion adjustment unit 614, and a chromatic dispersion compensation unit 615. For example, the chromatic dispersion compensation device 6A is implemented by a computer. A memory included in the computer stores a program constituting an information processing application for implementing the functions of the Hilbert transformer 611, the unwrapping unit 612, the difference acquisition unit 613, the chromatic dispersion adjustment unit 614, and the chromatic dispersion compensation unit 615. A processor included in the computer reads the information processing application from the memory and executes it to implement the functions of the Hilbert transformer 611, the unwrapping unit 612, the difference acquisition unit 613, the chromatic dispersion adjustment unit 614, and the chromatic dispersion compensation unit 615.

[0060] The Hilbert transformer 611 performs a Hilbert transform on the reference interference signal and the measurement interference signal. The signals obtained by performing the Hilbert transform on the reference interference signal and the measurement interference signal are output from the Hilbert transformer 611 to an unwrapping unit 612. The unwrapping unit 612 unwraps the Hilbert transformed reference interference signal and measurement interference signal. The unwrapped signals are output from the unwrapping unit 612 to a difference acquiring unit 613. The difference acquiring unit 613 calculates a correction term for chromatic dispersion as a compensation index based on the phase difference between the unwrapped reference interference signal and the measurement interference signal. The correction term calculated by the difference acquiring unit 613 is output to a chromatic dispersion amount adjusting unit 614.

[0061] The chromatic dispersion amount adjusting unit 614 is an adjusting unit that adjusts the amount of chromatic dispersion compensation to be set in the chromatic dispersion compensating unit 615 based on the compensation index acquired from the difference acquiring unit 613. For example, the chromatic dispersion amount adjusting unit 614 calculates the amount of chromatic dispersion compensation using preset calibration data or a calibration model related to the temperature dependency of the optical fiber.

[0062] The chromatic dispersion compensator 615 is a compensator that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the chromatic dispersion compensation amount set by the chromatic dispersion amount adjuster 614. For example, the chromatic dispersion compensator 615 is configured to include a chromatic dispersion member having the same or similar chromatic dispersion amount as that of the measurement interferometer. By including the chromatic dispersion member, the chromatic dispersion compensator 615 can compensate for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal. The chromatic dispersion member can be, for example, a holey fiber, a dispersion fiber, a dispersion compensation module, or a dispersion compensation film. By including a holey fiber or a dispersion fiber, the chromatic dispersion compensator 615 can compensate for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0063] Next, a hardware configuration for realizing the functions of the chromatic dispersion compensation apparatus 6A according to the first embodiment will be described. FIG. 9 is a block diagram showing a hardware configuration for realizing the functions of the chromatic dispersion compensation apparatus 6A according to the first embodiment. The functions of the Hilbert transformer 611, unwrapping unit 612, difference acquisition unit 613, chromatic dispersion amount adjustment unit 614, and chromatic dispersion compensation unit 615 provided in the chromatic dispersion compensation apparatus 6A are realized by processing circuits. That is, the chromatic dispersion compensation apparatus 6A includes processing circuits for executing the processing of each step shown in FIGS. 5 and 6 . The processing circuit may be a CPU (Central Processing Unit) that executes a program stored in a memory.

[0064] The Hilbert transformer 611 acquires the digital signals output from the reference interferometer 3 and the measurement interferometer 4, for example, via the input interface 100. If the digital signals are stored in a storage unit included in the chromatic dispersion compensation device 6A, the Hilbert transformer 611 may acquire the digital signals by reading them from the storage unit via the input interface 100. The chromatic dispersion compensator 615 performs compensation processing on the chromatic dispersion member, for example, via the output interface 101.

[0065] The functions of the Hilbert transformer 611, unwrapper 612, difference acquirer 613, chromatic dispersion amount adjuster 614, and chromatic dispersion compensator 615 included in the chromatic dispersion compensation device 6A are realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 103.

[0066] The processor 102 reads and executes programs stored in the memory 103 to implement the functions of the Hilbert transformer 611, unwrapping unit 612, difference acquisition unit 613, chromatic dispersion amount adjustment unit 614, and chromatic dispersion compensation unit 615 included in the chromatic dispersion compensation apparatus 6A. For example, the chromatic dispersion compensation apparatus 6A includes a memory 103 for storing programs that, when executed by the processor 102, result in the processing of each step shown in FIGS. 5 and 6 being executed. These programs cause a computer to execute the procedures or methods of the processing performed by the Hilbert transformer 611, unwrapping unit 612, difference acquisition unit 613, chromatic dispersion amount adjustment unit 614, and chromatic dispersion compensation unit 615. The memory 103 may be a computer-readable storage medium that stores programs for causing a computer to function as the Hilbert transformer 611, unwrapping unit 612, difference acquisition unit 613, chromatic dispersion amount adjustment unit 614, and chromatic dispersion compensation unit 615.

[0067] The memory 103 may be, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically-EPROM) (registered trademark), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD.

[0068] Some of the functions of the Hilbert transformer 611, unwrapper 612, difference acquirer 613, chromatic dispersion amount adjuster 614, and chromatic dispersion compensator 615 included in the chromatic dispersion compensation device 6A may be realized by dedicated hardware, and the other functions may be realized by software or firmware. For example, the function of the chromatic dispersion compensator 615 may be realized by a processing circuit that is dedicated hardware, and the functions of the Hilbert transformer 611, unwrapper 612, difference acquirer 613, and chromatic dispersion amount adjuster 614 may be realized by the processor 102 reading and executing a program stored in the memory 103. In this way, the processing circuit can realize the above functions by hardware, software, firmware, or a combination of these.

[0069] As described above, the chromatic dispersion compensation device 6 according to the first embodiment is a chromatic dispersion compensation device 6 that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal in the optical distance measuring device 1, and includes a chromatic dispersion compensation unit 61 that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on a set chromatic dispersion compensation amount, and a chromatic dispersion amount adjustment unit 62 that adjusts the chromatic dispersion compensation amount set in the chromatic dispersion compensation unit 61 based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal. The chromatic dispersion compensation amount is adjusted based on the compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal, and the difference in chromatic dispersion between the reference interference signal and the measurement interference signal is compensated for based on the adjusted chromatic dispersion compensation amount. This allows the chromatic dispersion compensation device 6 to reduce the impact of the difference in chromatic dispersion between the reference interference signal and the measurement interference signal on measurement accuracy.

[0070] The chromatic dispersion compensation device 6A according to the first embodiment includes a Hilbert transformer 611 that performs a Hilbert transform on the reference interference signal and the measurement interference signal, an unwrapping unit 612 that unwraps the Hilbert transformed reference interference signal and the measurement interference signal, and a difference acquiring unit 613 that calculates a correction term based on the phase difference between the unwrapped reference interference signal and the measurement interference signal. As a result, the chromatic dispersion compensation device 6A can obtain a compensation index for compensating for the difference in chromatic dispersion between the reference interferometer 3 and the measurement interferometer 4.

[0071] In the chromatic dispersion compensation device 6 according to the first embodiment, the chromatic dispersion amount adjusting unit 62 periodically acquires the compensation index, and adjusts the amount of chromatic dispersion compensation to be set in the chromatic dispersion compensating unit 61 based on the acquired compensation index. This allows the chromatic dispersion compensation device 6 to perform chromatic dispersion compensation using simple signal processing for acquiring the compensation index, without having to frequently acquire the compensation index.

[0072] In the chromatic dispersion compensation devices 6 and 6A according to the first embodiment, the compensation index is a correction term that represents the phase difference due to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal. By using this correction term, the chromatic dispersion compensation devices 6 and 6A can determine the amount of chromatic dispersion compensation that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0073] In the chromatic dispersion compensation device 6 according to the first embodiment, the chromatic dispersion compensation unit 61 includes a chromatic dispersion member having the same or similar amount of chromatic dispersion as that of the measurement interferometer. By including the chromatic dispersion member, the chromatic dispersion compensation unit 61 can compensate for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0074] In the chromatic dispersion compensation device 6 according to the first embodiment, the chromatic dispersion compensator 61 includes a holey fiber or a dispersive fiber. By including the holey fiber or the dispersive fiber, the chromatic dispersion compensator 61 can compensate for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0075] The optical distance measuring device 1 according to the first embodiment includes a wavelength swept light source 2 that outputs wavelength swept light, a reference interferometer 3 that has two optical paths with different optical path lengths and generates a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths, a measurement interferometer 4 that has an optical path that passes through an object TG and an optical path that does not pass through the object TG and generates a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths, a resampling unit 51 that resamples the measurement interference signal based on the reference interference signal, and a Fourier transform of the resampled measurement interference signal. the optical distance measuring device 1 includes an FFT unit 52 that calculates an optical path length difference between the reference interference signal and the measurement interference signal based on the peak position of the spectrum obtained by Fourier transform, a distance measuring unit 53 that calculates an optical path length difference between the reference interference signal and the measurement interference signal based on the calculated optical path length difference, an FB unit 54 that calculates a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the phase difference between the reference interference signal and the measurement interference signal, a chromatic dispersion compensation unit 61 that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the set chromatic dispersion compensation amount, and a chromatic dispersion amount adjustment unit 62 that adjusts the chromatic dispersion compensation amount set in the chromatic dispersion compensation unit 61 based on the compensation index obtained from the FB unit 54. This enables the optical distance measuring device 1 to reduce the effect on measurement accuracy caused by the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0076] In the optical distance measuring device 1 according to the first embodiment, the resampling unit 51 samples the measurement interference signal at the time when the rising edge of the reference interference signal crosses zero, thereby enabling the optical distance measuring device 1 to resample the measurement interference signal in synchronization with the reference interference signal.

[0077] The chromatic dispersion compensation method according to the first embodiment includes step ST1B in which the chromatic dispersion amount adjusting unit 62 adjusts the amount of chromatic dispersion compensation set in the chromatic dispersion compensating unit 61 based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal, and step ST2B in which the chromatic dispersion compensating unit 61 compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the amount of chromatic dispersion compensation set by the chromatic dispersion amount adjusting unit 62. By having the chromatic dispersion compensation device 6 perform the above method, it is possible to reduce the impact on measurement accuracy caused by the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0078] Various aspects of the present disclosure are summarized below as appendices.

[0079] (Supplementary Note 1) A chromatic dispersion compensation device for compensating for a difference in chromatic dispersion between the reference interference signal and the measurement interference signal in an optical distance measuring device including: a wavelength swept light source that outputs wavelength swept light; a reference interferometer that has two optical paths with different optical path lengths and that generates a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; and a measurement interferometer that has an optical path that passes through an object and an optical path that does not pass through the object and that generates a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths, the chromatic dispersion compensation device comprising: a compensator that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on a set chromatic dispersion compensation amount; and an adjuster that adjusts the chromatic dispersion compensation amount to be set in the compensator based on a compensation index according to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0080] (Supplementary Note 2) The chromatic dispersion compensation device according to Supplementary Note 1, comprising: a Hilbert transform unit that performs a Hilbert transform on the reference interference signal and the measurement interference signal; an unwrapping unit that unwraps the Hilbert transformed reference interference signal and the measurement interference signal; and a difference acquisition unit that calculates the compensation index based on a phase difference between the unwrapped reference interference signal and the measurement interference signal.

[0081] (Supplementary Note 3) The chromatic dispersion compensation device according to Supplementary Note 1 or Supplementary Note 2, characterized in that the adjustment unit periodically acquires the compensation index and adjusts the amount of chromatic dispersion compensation to be set in the compensation unit based on the acquired compensation index.

[0082] (Supplementary Note 4) The chromatic dispersion compensation device according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the compensation index is a correction term that represents a phase difference due to a difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

[0083] (Supplementary Note 5) The chromatic dispersion compensation device according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the compensation section includes a chromatic dispersion member having an amount of chromatic dispersion that is the same as or similar to that of the measurement interferometer.

[0084] (Supplementary Note 6) The chromatic dispersion compensation device according to Supplementary Note 5, wherein the compensation section includes a holey fiber or a dispersion fiber.

[0085] a wavelength swept light source that outputs wavelength swept light; a reference interferometer system having two optical paths with different optical path lengths, and generating a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; a measurement interferometer system having an optical path that passes through an object and an optical path that does not pass through the object, and generating a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; a resampling unit that resamples the measurement interference signal based on the reference interference signal; a Fourier transform unit that Fourier transforms the resampled measurement interference signal; a distance measuring unit that calculates an optical path length difference of the measurement interferometer system based on a peak position of a spectrum obtained by the Fourier transform, and measures a distance to the object based on the calculated optical path length difference; a feedback unit that calculates a compensation index according to a difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on a phase difference between the reference interference signal and the measurement interference signal; an adjustment unit that adjusts the amount of chromatic dispersion compensation to be set in the chromatic dispersion compensator based on the compensation index acquired from the feedback unit.

[0086] (Supplementary Note 8) The optical distance measuring device according to Supplementary Note 7, wherein the resampling unit samples the measurement interference signal at a time when a rising edge of the reference interference signal crosses zero.

[0087] (Supplementary Note 9) A chromatic dispersion compensation method for compensating for a difference in chromatic dispersion between the reference interference signal and the measurement interference signal in an optical distance measuring device including: a wavelength swept light source that outputs wavelength swept light; a reference interferometer that has two optical paths with different optical path lengths and that generates a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; and a measurement interferometer that has an optical path that passes through an object and an optical path that does not pass through the object and that generates a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths, the method comprising: an adjusting unit adjusting an amount of chromatic dispersion compensation based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal; and a compensating unit compensating for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the amount of chromatic dispersion compensation set by the adjusting unit.

[0088] Any of the components of the embodiments may be modified or omitted.

[0089] A chromatic dispersion compensation device according to the present disclosure can be used in, for example, an optical distance measuring device.

[0090] REFERENCE SIGNS LIST 1 Optical distance measuring device, 2 Wavelength swept light source, 3 Reference interferometer system, 4 Measurement interferometer system, 5 Signal processing unit, 6, 6A Wavelength dispersion compensation device, 7 Optical coupler, 8 Optical tube, 21 Electrical unit, 22 Light source, 31, 32, 41, 43 Optical coupler, 33, 44 Photoelectric conversion unit, 34, 45 AD conversion unit, 42 Circulator, 51 Resampling unit, 52 FFT unit, 53 Distance measuring unit, 54 FB unit, 61, 615 Wavelength dispersion compensation unit, 62, 614 Wavelength dispersion amount adjustment unit, 100 Input interface, 101 Output interface, 102 Processor, 103 Memory, 541, 611 Hilbert transform unit, 542, 612 Unwrap unit, 543, 613 Difference acquisition unit.

Claims

1. A chromatic dispersion compensation device for an optical distance measuring device comprising: a wavelength swept light source that outputs wavelength swept light; a reference interferometer that has two optical paths with different optical lengths and generates a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; and a measurement interferometer that has an optical path that passes through an object and an optical path that does not pass through the object and generates a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths, the chromatic dispersion compensation device compensating for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal, the chromatic dispersion compensation device comprising: a compensator that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on a set chromatic dispersion compensation amount; and an adjuster that adjusts the chromatic dispersion compensation amount to be set in the compensator based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

2. The chromatic dispersion compensation device according to claim 1, further comprising: a Hilbert transform unit that performs a Hilbert transform on the reference interference signal and the measurement interference signal; an unwrapping unit that unwraps the Hilbert transformed reference interference signal and the measurement interference signal; and a difference acquisition unit that calculates the compensation index based on a phase difference between the unwrapped reference interference signal and the measurement interference signal.

3. A chromatic dispersion compensation device according to claim 1 or claim 2, characterized in that the adjustment unit periodically acquires the compensation index and adjusts the amount of chromatic dispersion compensation to be set in the compensation unit based on the acquired compensation index.

4. A chromatic dispersion compensation device according to any one of claims 1 to 3, characterized in that the compensation index is a correction term that represents a phase difference due to a difference in chromatic dispersion between the reference interference signal and the measurement interference signal.

5. A wavelength dispersion compensation device according to any one of claims 1 to 4, characterized in that the compensation section includes a wavelength dispersion member having the same or similar amount of wavelength dispersion as that of the measurement interferometer system.

6. The chromatic dispersion compensation device according to claim 5, wherein the compensation section includes a holey fiber or a dispersion fiber.

7. A wavelength swept light source that outputs wavelength swept light; a reference interferometer system having two optical paths with different optical path lengths, and generating a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; a measurement interferometer system having an optical path that passes through an object and an optical path that does not pass through the object, and generating a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; a resampling unit that resamples the measurement interference signal based on the reference interference signal; a Fourier transform unit that Fourier transforms the resampled measurement interference signal; a distance measuring unit that calculates an optical path length difference of the measurement interferometer system based on the peak position of the spectrum obtained by the Fourier transform, and measures the distance to the object based on the calculated optical path length difference; a feedback unit that calculates a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the phase difference between the two signals; and a compensation unit that compensates for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on a set chromatic dispersion compensation amount. an adjusting unit that adjusts the amount of chromatic dispersion compensation to be set in the compensating unit based on the compensation index acquired from the feedback unit.

8. The optical distance measuring device according to claim 7, wherein the resampling section samples the measurement interference signal at the time when the rising edge of the reference interference signal crosses zero.

9. A chromatic dispersion compensation method for compensating for a difference in chromatic dispersion between the reference interference signal and the measurement interference signal in an optical distance measuring device equipped with: a wavelength swept light source that outputs wavelength swept light; a reference interferometer that has two optical paths with different optical lengths and generates a reference interference signal by photoelectrically converting reference interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths; and a measurement interferometer that has an optical path that passes through an object and an optical path that does not pass through the object and generates a measurement interference signal by photoelectrically converting measurement interference light obtained by combining the wavelength swept light that has passed through each of the two optical paths, the method comprising: an adjustment unit adjusting an amount of chromatic dispersion compensation based on a compensation index corresponding to the difference in chromatic dispersion between the reference interference signal and the measurement interference signal; and a compensation unit compensating for the difference in chromatic dispersion between the reference interference signal and the measurement interference signal based on the amount of chromatic dispersion compensation set by the adjustment unit.

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