Optical range finder and evaluation method thereof

Abstract

To make it possible to measure a distance highly accurately without a measurement error arising from a distribution of a group delay in a cross section of a measurement light beam when, in an optical distance meter, irradiating the measurement object with modulation light from a light projector, and calculating, by a signal processing unit, the distance to a measurement object from a time lag of a measurement signal obtained by detecting the returning modulation light reflected upon the measurement object.SOLUTION: An optical distance meter is provided with a light projector composed of a reflective optical system irradiating a measurement object 1 with modulation light having intensity or a phase periodically modulated as measurement light. A distance to the measurement object 1 is calculated on the basis of: returning measurement light SS'in which measurement light SS with which the measurement object 1 is irradiated via the light projector is reflected by the measurement object 1, an overlapping interference optical system as reference light SR having intensity or a phase periodically modulated, and an interference signal to be obtained by the interference optical system between the returning measurement light SS' reflected by the measurement object 1 and the reference light SR.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention is an optical distance meter that irradiates a measured object with modulated light from a light projecting unit, detects the modulated light reflected by the measured object and returns with a light receiving unit, and calculates the distance to the measured object from the time delay of the measurement signal obtained by the light projecting unit and the signal processing unit. and its evaluation method Regarding. [Background technology]

[0002] Conventionally, distance measurement based on optical principles using laser light has been known as an active distance measurement method capable of measuring the distance to a precise point. In a laser rangefinder that uses laser light to measure the distance to a target object, the distance to the target object is calculated based on the difference between the time when the laser light is emitted and the time when the laser light reflected from the target object is detected by a light receiving element. In addition, for example, the driving current of a semiconductor laser is modulated with a triangular wave or the like, and the reflected light from the target object is received by a photodiode embedded in the semiconductor laser element, and distance information is obtained from the main wave number of the sawtooth wave that appears in the photodiode output current.

[0003] The present inventors have previously proposed a range finder configured as shown in FIG. 12 as a range finder capable of measuring long distances with high accuracy and in a short time (see, for example, Patent Document 1).

[0004] The laser range finder 200 includes a first light source 210 that emits a measurement light S1, a second light source 220 that emits a reference light S2, a prism unit 230 into which the measurement light S1 emitted from the first light source 210 and the reference light S2 emitted from the second light source 220 are incident via polarization-preserving collimators 211, 212, a measurement surface 250 and a reference surface 255 onto which the measurement light S1 emitted from the first light source 210 is irradiated via the prism unit 230, and a measurement surface 250 and a reference surface 255 into which the measurement light S1 emitted from the first light source 210 and the reference light S2 emitted from the second light source 220 are superimposed via the prism unit 230 and incident, The optical fiber 200 includes a first optical detector 260 which detects interference light with illumination light S2, a second optical detector 270 which detects interference light between the reflected light of the measurement light irradiated onto the measurement surface 250 and the reflected light of the reference light irradiated onto the reference surface 255, which are superimposed and incident via the prism unit 230, and the reflected light of the measurement light and the reflected light of the reference light, and a signal processing unit 280 which calculates a difference between the distance to the reference surface 255 and the distance to the measurement surface 250 from the speed of light and the refractive index at the measurement wavelength, based on the time difference between the interference signal detected by the first optical detector 260 and the interference signal detected by the second optical detector 270.

[0005] In this laser rangefinder 200, the prism unit 230 is an interferometer prism having a structure in which a first trapezoidal prism 231, a first right-angle prism 232, a second right-angle prism 233, a third right-angle prism 234, a second trapezoidal prism 235, and a fourth right-angle prism 236 are bonded together to form an integrated structure.

[0006] The first photodetector 260 detects interference light between the measurement light S1 and the reference light S2, and detects the measurement light S1 that is superimposed on the beam splitter film 242A formed on the first trapezoidal prism 231 of the prism unit 230 and split into two. 11 ,S 12 and the reference beam S 21 ,S 22The interference light between these two beams is detected by two photodetectors 261A and 261B, and the difference between these beams is detected by a differential detector 262.

[0007] The second photodetector 270 detects the reflected light S from the measurement surface 250. 1C ' and the reflected light S from the reference surface 255 2C The interference light of the reflected light S′ is detected by the beam splitter film 242B formed on the second trapezoidal prism 235 of the prism unit 230, which is superimposed on the reflected light S and split into two. 11 ',S 12 ' and reflected light S 21 ',S 22 The interference light between the first and second light beams ' and ' is detected by two photodetectors 271A and 271B, and the difference between the detected light beams is detected by a differential detector 272.

[0008] The signal processing unit 280 detects the time difference of an interference signal obtained by detecting the interference light between the measurement light S1 and the reference light S2 by the first photodetector 260, and detects the reflected light S from the measurement surface 250 by the second photodetector 270. 1C ' and the reflected light S from the reference surface 255 2C Based on the time difference of the interference signals obtained by detecting the interference light of ', a process is performed to obtain the difference in distance between the reference surface 255 and the measurement surface 250 from the speed of light and the refractive index at the measurement wavelength.

[0009] In this laser distance meter 200, the difference in optical distance experienced by the measurement light S1 and the reference light S2 within the prism unit 230 until they are detected as each interference light by the first and second photodetectors 260, 270 is equal to each other, and even if the temperature of the prism unit 230 changes, the relative relationship between the each interference light detected by the first and second photodetectors 260, 270 is constant, making it possible to perform high-precision optical interference observation, and the signal processing unit 280 can obtain measurement values ​​such as displacement, distance, or distribution from the interference signal detected by the first photodetector 260 and the interference signal detected by the second photodetector 270. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 5588769 Summary of the Invention [Problem to be solved by the invention]

[0011] Conventionally, optical rangefinders that irradiate modulated light from a light-projecting unit onto an object to be measured, and then detect the modulated light reflected by the object and returned by a light-receiving unit to obtain a measurement signal, from which the distance to the object is calculated by a signal processing unit from the time delay have adopted refractive optical systems that use optical lenses as optical systems such as a collimator that converts the modulated light emitted from a light source into parallel light, and a focuser that converts the modulated light incident on the light-receiving unit into convergent light.

[0012] The present inventors have examined how the difference in group velocity optical path difference distance experienced by a propagating laser light beam when passing through a refractive optical system in an optical distance meter affects optical distance measurement distortion.

[0013] Specifically, we investigated how the difference in group velocity optical path difference distance experienced by a beam passing through polarization-preserving collimators 211, 212 of the laser rangefinder 200 in the previously proposed Patent Document 1 is distributed within the beam, and how this affects optical distance measurement distortion.

[0014] As shown in Figure 13, for a collimator lens made of a glass material with a refractive index n = 1.5712 and a group refractive index ng = 1.5907, the distance experienced by each light ray from focal position A to position B where the beam becomes parallel was calculated using the phase velocity and group velocity. The distribution of the phase velocity distance and group velocity distance measured from focal position A within the beam is shown in Figure 14, where the distance is distributed within the beam cross section, with the distance being shorter at the periphery compared to the center.

[0015] That is, the beam that has passed through the collimator lens has a constant phase velocity distance and becomes an equiphase plane within the parallel beam, as shown in FIG.

[0016] Here, if the wavelength is λ and the frequency is f, the wave number k is expressed as k = 2π / λ, and the angular frequency ω is expressed as ω = 2πf. The phase velocity v, which is the speed at which the points of equal phase of one wave travel, is p is v p =ω / k, and the velocity at which the two waves travel at the point where the phase difference is equal is called group velocity v g is v g =dω / dk. In a vacuum, the phase velocity v p and group velocity v g The speed at which the pulse waveform of the optical comb travels is the group velocity v g It is.

[0017] If the speed of light in a vacuum is c, then the phase velocity in a medium with a refractive index of n is v p is v p =c / n, and the angular frequency ω is expressed as ω=ck=2πc / λ. Also, the group velocity v g is v g =c / n g It is expressed as n g is the group index, and n g =c / v g It is expressed as:

[0018] When light travels through a medium with a refractive index n and a distance L, the time it takes for a set of points with equal phase, i.e., an equal phase front, to propagate is expressed as τ, the optical distance nL, which is the distance L multiplied by the refractive index n, divided by the speed of light c. τ=L / v p =nL / c

[0019] On the other hand, the time it takes for the envelope of the pulse waveform to propagate at the point where the phase difference is equal is expressed as τ g It is expressed as: τ g =L / v g =n g L / c=L(n-λdn / dλ) / c

[0020] The time it takes for the envelope of the pulse waveform to propagate is τ g Since there is a term for the wavelength dependence of the refractive index in , the time τ for the equiphase front to propagate and the time τ for the envelope of the pulse waveform to propagate g There is a time lag.

[0021] group velocity v g is the phase velocity v p The optical path difference through the glass material causes the peripheral part of the lens to pass through the lens faster than the center of the lens, so the outer light travels ahead. When an evaluation was performed using an evaluation experiment system 300 configured as shown in FIG. 16, it was found that when a laser beam with a mode field diameter (MFD) of 3.5 mm passes through a lens, the laser beam is accelerated by 1 / e with the center position of the laser beam and the power density at the center of the beam as the reference. 2 There is a distance difference of about 3 μm between the outer position where the power density is attenuated to 1000 μm and the outer position where the power density is attenuated to 1000 μm.

[0022] In the evaluation experimental system 300, a measurement light beam from the rangefinder head 301 is irradiated onto the center of the retroreflector 304 via the adjustment mirrors 302A, 302B and the optical chopper 303. The measurement light beam is reflected by the retroreflector 304 and returns to the rangefinder head 301. The measurement light beam is blocked from one side on each of the outbound and return paths by the optical chopper 303, so that the beam is cut from both sides in a point-symmetric manner due to the mirror image relationship of the retroreflector 304. As shown in Figure 17, from state 0 where the entire beam returns, the beam is gradually cut from both sides, with the center of the beam remaining until the end (states 1 to 5), and when the beam leaves the blades of the optical chopper, the beam is restored from the center of the beam (states 5 to 9), and this process is repeated.

[0023] In the evaluation experimental system 300, the results of repeatedly measuring the distance to the retroreflector 304 are shown in Figure 18. As the measurement light beam returning to the rangefinder head 301 changes from state 0 to state 9, a convex distance fluctuation occurs on the downward side. In the center of the measurable section, the entire beam is used for measurement, and the distance is shorter because the peripheral beam is included, whereas near the boundary where the distance cannot be measured, the distance is longer because only the center of the measurement light beam is used to measure the distance.

[0024] It was found that in optical distance meters, if there is a group delay distribution in the cross section of the measurement light beam, a distance difference of several μm may occur between the center and periphery of the beam. It was also found that if only a part of the beam cross section is detected, a distance error of several μm may occur compared to when the entire beam is detected by a mirror or retroreflector.

[0025] The present invention has been devised in consideration of the above-mentioned problems in the conventional art, and its object is to enable high-precision measurement of distances in an optical rangefinder by eliminating measurement errors caused by the difference in group velocity optical path difference distance experienced when a propagating laser light beam passes through a refractive optical system, i.e., the distribution of group delay in the cross section of the measurement light beam.

[0026] Another object of the present invention is to make it possible to measure the same distance even when only a portion of the beam area is detected as when the entire beam is detected.

[0027] Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the following description of the embodiments. [Means for solving the problem]

[0028] In the present invention, a reflective optical system is used instead of a refractive optical system in order to eliminate the distribution of group delay in the cross section of the measurement light beam.

[0029] That is, the present invention is an optical distance meter, comprising: a light projection unit including a reflection optical system that irradiates a measurement object with light whose intensity or phase is periodically modulated as measurement light; a reflective scanning optical system that scans a measurement object with the measurement light emitted from the light projecting unit; The above light projecting section to the reflection type scanning optical system The measurement light is reflected by the measurement object through the The measurement light returned from the reflection type scanning optical system through the light projecting unit isan interference optical system that superimposes the measurement light with a reference light whose intensity or phase is periodically modulated; a light receiving unit that receives interference light between the measurement light and the reference light, which is obtained by the interference optical system and is reflected and returned by the measurement object; and a signal processing unit that receives as input a measurement signal, which is an interference signal obtained as a detection output of the interference light by the light receiving unit; the interference optical system causes interference light between the measurement light irradiated from the light projecting unit through the reflective scanning optical system to the measurement object and reflected by the measurement object and returned from the reflective scanning optical system through the light projecting unit, and the reference light to be incident on the light receiving unit; The signal processing unit calculates a distance to the object by performing an analysis based on a relative relationship between the measurement signal and a reference signal which is a signal generating the measurement light or the reference light or a signal generated by the measurement light or the reference light. Then, the absolute distances to a plurality of points on the object are measured to obtain a three-dimensional image. It is characterized by: In the optical rangefinder according to the present invention, the light-projecting unit consisting of the reflective optical system can be one in which the group delay distribution has been evaluated by an evaluation experimental system which irradiates a measurement light beam onto the center of a retroreflector via an optical chopper and evaluates the group delay distribution on a cross section of the measurement light beam reflected by the retroreflector and returning via the optical chopper.

[0030] In the optical rangefinder of the present invention, the reflective optical system provided in the light-projecting unit is a reflective collimator that converts modulated light emitted into space from the light output end into parallel light, and the light output end can be a part that outputs light from a light source into space, or a part that outputs light into space at the end of an optical path extended from the light source by an optical waveguide.

[0031] In addition, the optical rangefinder of the present invention can be configured so that, as the reflective optical system, the light-projecting section includes a reflective collimator that converts modulated light into parallel light, and the light-receiving section includes a reflective focuser that converts the interference light obtained by the interference optical system into convergent light and makes it incident on the light-receiving element.

[0032] In addition, the optical rangefinder of the present invention may include a reflective scanning optical system that scans the object to be measured with measurement light emitted from the light-projecting unit, and the interference optical system may cause interference light between the measurement light and the reference light reflected by the object to be measured and returned via the scanning optical system to be incident on the light-receiving unit.

[0033] In addition, in the optical rangefinder of the present invention, the interference optical system can separate modulated light emitted from the light source as measurement light through the light-projecting unit into reference light and measurement light, irradiate the reference light that has passed through a reference optical path onto the object to be measured, and superimpose the measurement light that has been reflected by the object to be measured and returned to obtain interference light.

[0034] In addition, the optical rangefinder according to the present invention may include two light-projecting sections, each consisting of a reflective optical system, into which the modulated light emitted into space from the optical output end is branched and incident, and the interference optical system may irradiate the modulated light emitted from one of the light-projecting sections as measurement light onto the object to be measured, and superimpose the measurement light reflected and returned by the object to be measured and the modulated light emitted from the other light-projecting section as reference light to obtain interference light.

[0035] In addition, the optical rangefinder according to the present invention includes two light sources that radiate mutually coherent modulated light into space, and two light-projecting units, each consisting of a reflective optical system into which the modulated light radiated into space from the two light sources is incident. The interference optical system irradiates the modulated light emitted from one of the light-projecting units as measurement light onto the object to be measured, and superimposes the measurement light reflected and returned by the object to be measured with the modulated light emitted from the other light-projecting unit as a reference light to obtain interference light.

[0036] In addition, the optical rangefinder according to the present invention may include two light-projecting sections, each consisting of a reflective optical system, into which the modulated light emitted from the optical output end into space is branched and incident, and the interference optical system may irradiate the modulated light emitted from one of the light-projecting sections as measurement light onto the object to be measured, and superimpose the measurement light reflected and returned by the object to be measured and the modulated light emitted from the other light-projecting section and passed through the reference optical path as reference light to obtain interference light.

[0037] Moreover, the optical rangefinder according to the present invention may include a reference light-receiving unit that receives reference interference light obtained by superimposing the modulated light emitted from the one light-projecting unit as measurement light and the modulated light emitted from the other light-projecting unit as reference light, and the interference optical system superimposes the modulated light emitted from the other light-projecting unit as reference light on the measurement light reflected and returned by the object to be measured to obtain measurement interference light, and causes the measurement interference light to be incident on the light-receiving unit, and also obtains reference interference light obtained by superimposing the modulated light emitted from the one light-projecting unit as measurement light and the modulated light emitted from the other light-projecting unit as reference light, and causes the reference interference light to be incident on the reference light-receiving unit, and the signal processing unit calculates the distance to the object to be measured from the time difference between a measurement signal obtained as a detection output of the measurement interference light by the light-receiving unit and a reference signal obtained as a detection output of the reference interference light by the reference light-receiving unit.

[0038] In addition, in the optical rangefinder according to the present invention, the reference light receiving unit may be equipped with a reflective focuser that converts the reference interference light obtained by the interference optical system into convergent light and makes it incident on the light receiving element.

[0039] In addition, in the optical rangefinder according to the present invention, the two light sources can be optical comb light sources that output measurement light and reference light whose intensity or phase is periodically modulated and whose modulation periods are different from each other, and the interference optical system can be an optical comb interferometer.

[0040] Furthermore, in the optical range finder according to the present invention, the optical comb interferometer may be a fiber-optic comb interferometer, and may include a reflective optical system that irradiates measurement light emitted into space via the fiber-optic comb interferometer onto the object to be measured, and causes the measurement light reflected by the object to be measured and returned to be incident on the fiber-optic comb interferometer. Also, The present invention is an evaluation method for evaluating the group delay distribution of measurement light emitted from a light projecting unit of an optical range finder, characterized in that a measurement light beam is irradiated onto the center of a retroreflector via an optical chopper, and the group delay distribution is evaluated in a cross section of the measurement light beam that is reflected by the retroreflector and returns via the optical chopper. . Effect of the Invention

[0041] In the optical rangefinder of the present invention, unlike refractive optical systems that use optical lenses, the path of light passes through air which has little dispersion, and therefore a reflective optical system using flat, concave, convex or other reflecting mirrors which are less likely to produce group delay distribution in the cross section of the beam is used instead of the refractive optical system.This eliminates measurement errors caused by the distribution of group delay in the cross section of the measurement light beam, and enables distance to be measured with high accuracy.

[0042] Furthermore, in the optical rangefinder of the present invention, by eliminating measurement errors resulting from the distribution of group delay in the cross section of the measurement light beam, it is possible to measure the same distance even when only a portion of the beam area is detected as when the entire beam is detected.

[0043] That is, in the optical distance meter of the present invention, the interference optical system causes the interference light between the measurement light and the reference light, which is reflected by the measurement object and returned from the reflective scanning optical system through the light projecting unit from the light projecting unit consisting of a reflective optical system, to be incident on the light receiving unit. Therefore, a group delay distribution is unlikely to occur in the beam cross section of the measurement light in the light projecting unit consisting of the reflective optical system. Also, in the reflective scanning optical system that scans the measurement object with the measurement light emitted from the light projecting unit, a group delay distribution is unlikely to occur in the beam cross section of the measurement light and the reflected light, and there is no group velocity optical path difference, so that the absolute distance to the surface of the measurement object can be measured with high accuracy, and the three-dimensional shape of the object can be measured non-contact by accumulating the beam irradiation position and the absolute distance to that location for multiple points. In addition, in an evaluation method for evaluating the group delay distribution of measurement light emitted from the light-projecting unit of an optical rangefinder according to the present invention, a measurement light beam is irradiated onto the center of a retroreflector via an optical chopper, and the group delay distribution is evaluated at the cross section of the measurement light beam reflected by the retroreflector and returning via the optical chopper, thereby making it possible to evaluate the group delay distribution of the measurement light emitted from the light-projecting unit of the optical rangefinder. Therefore, according to the present invention, it is possible to provide a high-quality optical rangefinder in which the group delay distribution of the measurement light emitted from the light-projecting unit has been evaluated. [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a schematic diagram showing a configuration of a laser range finder to which the present invention is applied. [Diagram 2] 4 is a cross-sectional view showing the structure of a reflective collimator constituting a light projecting unit of the laser rangefinder. FIG. [Diagram 3] FIG. 2 is a plan view illustrating a schematic configuration of a prism unit provided in the laser rangefinder. [Figure 4] FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. [Diagram 5] FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. [Figure 6] FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. [Figure 7] FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. [Figure 8] FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. [Figure 9] FIG. 13 is a schematic diagram showing another example of the configuration of an optical rangefinder to which the present invention is applied. [Figure 10] FIG. 13 is a schematic diagram showing still another configuration example of the optical range finder to which the present invention is applied. [Figure 11] 1 is a schematic diagram showing an example of the configuration of an optical three-dimensional shape measuring device to which the present invention is applied; [Figure 12] FIG. 1 is a schematic diagram showing a configuration of a laser range finder proposed by the present inventors. [Figure 13] 2 is a diagram showing a schematic diagram of the path of each light ray from the focal position of a collimator lens to the position where the light ray passes through the collimator lens and becomes parallel. FIG. [Figure 14] FIG. 13 is a diagram showing the distribution of phase velocity distance and group velocity distance within a beam measured from the focal position of the collimator lens. [Figure 15] FIG. 2 is a diagram showing an equiphase surface of a beam that has passed through the collimator lens. [Figure 16] FIG. 1 is a schematic diagram showing a configuration of an evaluation experiment system for evaluating an optical path difference of light rays passing through a glass material. [Figure 17] FIG. 2 is a schematic diagram showing a state of a beam in which a light beam is blocked by a blade of an optical chopper in the above evaluation experiment system. [Figure 18] FIG. 11 is a diagram showing the results of repeatedly measuring the distance to a retroreflector in the above evaluation experiment system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Common components will be described with common reference numerals in the drawings. Furthermore, the present invention is not limited to the following examples, and can be modified as desired without departing from the gist of the present invention.

[0046] The present invention is applied to a laser range finder 100 having a configuration as shown in FIG.

[0047] This laser rangefinder 100 is an application of the present invention to the laser rangefinder proposed in the previously-mentioned Patent Document 1, and is equipped with a first light source 110 that emits S-polarized measurement light S1 via a reflective (polarization-preserving) collimator 111, a second light source 120 that emits S-polarized reference light S2 via a reflective (polarization-preserving) collimator 112, and a prism unit 130 into which the S-polarized measurement light S1 and reference light S2 are incident with their polarization directions adjusted via half-wavelength (λ / 2) plates 113, 114.

[0048] That is, the laser distance meter 100 includes a first light source 110 that emits a measurement light S1, a second light source 120 that emits a reference light S2, a prism unit 130 onto which the measurement light S1 emitted from the first light source 110 and the reference light S2 emitted from the second light source 120 are incident, a measurement surface 150 onto which the measurement light S1 emitted from the first light source 110 is irradiated via the prism unit 130, a reference surface 155 onto which the reference light S2 emitted from the second light source 120 is irradiated via the prism unit 130, and a reference surface 155 onto which the measurement light S1 emitted from the first light source 110 and the reference light S2 emitted from the second light source 120 are superimposed via the prism unit 130. the first photodetector 160 which is incident on the measurement surface 150 and detects interference light between the measurement light S1 and the reference light S2; the second photodetector 170 which detects interference light between the reflected light of the measurement light and the reflected light of the reference light which is incident on the reference surface 155 and superimposed via the prism unit 130, and which detects interference light between the reflected light of the measurement light and the reflected light of the reference light; and a signal processing unit 180 which calculates a difference between the distance to the reference surface 155 and the distance to the measurement surface 150 from the speed of light and the refractive index at the measurement wavelength, from the time difference between the interference signal detected by the first photodetector 160 and the interference signal detected by the second photodetector 170.

[0049] The first and second light sources 110, 120 each emit a coherent measurement light S1 and a reference light S2 whose intensity or phase is periodically modulated and whose modulation periods are different from each other. ....

[0050] The reflective (polarization-preserving) collimators 111 and 112 collimate the S-polarized measurement light S1 and reference light S2 emitted into space from the first and second light sources 110 and 120. Diverging light The reflective optical element functions as a light-projecting section that converts reflective light into parallel light. For example, as shown in FIG. 2, the reflective optical element is made up of parabolic mirrors 111a and 112a. Unlike a refractive optical system that uses optical lenses, the light path passes through air with little dispersion, making it difficult for group delay distribution to occur in the beam cross section.

[0051] In this laser range finder 100, first and second light sources 110 and 120 emit light via reflective (polarization-preserving) collimators 111 and 112. Diverging light The S-polarized measurement light S1 and reference light S2 are converted into parallel light from the polarized light and enter the prism unit 130. Since the light path passes through air with little dispersion, it is difficult for group delay distribution to occur in the beam cross section, and the light is entered into the prism unit 130 without a group velocity optical path difference.

[0052] As shown in FIG. 3, the prism unit 130 is an interferometer prism having a structure in which a first trapezoidal prism 131, a first right-angle prism 132, a second right-angle prism 133, a third right-angle prism 134, a second trapezoidal prism 135, and a fourth right-angle prism 136 are bonded together to form an integrated structure.

[0053] In this laser range finder 100, the prism unit 130 comprises a first trapezoidal prism 131 having two surfaces 131a and 131b perpendicular to the optical path and perpendicular to each other, and two surfaces 131c and 131d parallel to each other and at 45° to the optical path, with a beam splitter film 142A formed on one surface; a first right-angle prism 132 having an inclined surface 132c bonded to the surface 131d of the first trapezoidal prism 131 on which the beam splitter film 142A is formed, with the beam splitter film 142A sandwiched between them; and a polarizing beam splitter film 143 formed on one of the inclined surfaces, which is used to polarize the polarizing beam. The optical system includes a second right-angle prism 133 and a third right-angle prism 134 in which inclined surfaces 133c, 134c are bonded together with a beam splitter film 143 in between, a second trapezoidal prism 135 having two faces 135a, 135b which are perpendicular to the optical path and perpendicular to each other, and two faces 135c, 135d which are parallel to each other and at 45° to the optical path, and on one of which a beam splitter film 142B is formed, and a fourth right-angle prism 136 in which an inclined surface 136c is bonded to the face 135d of the second trapezoidal prism 135 on which the beam splitter film 142B is formed, with the beam splitter film 142B in between.

[0054] A surface 131c on the long side of the first trapezoidal prism 131 functions as a total reflection surface 141A. Similarly, a surface 135c on the long side of the second trapezoidal prism 135 functions as a total reflection surface 141B.

[0055] In the prism unit 130, one of the two surfaces 131a, 131b that form a right angle with respect to the optical path of the first trapezoidal prism 131 and one of the two surfaces 132a, 132b that form a right angle of the first rectangular prism 132 are attached to one of the two surfaces that form a right angle of the first rectangular prism 132 so that the beam splitter film 142A and the polarizing beam splitter film 143 form a right angle with each other. In addition, one of the two faces 132a, 132b that form a right angle to the optical path of the second trapezoidal prism 135 and one of the two faces 136a, 136b that form a right angle of the fourth right angle prism 136 are bonded to one of the two faces that form a right angle of the second right angle prism 133 so that the beam splitter film 142B and the polarizing beam splitter film 143 are parallel to each other.

[0056] The prism unit 130 is a trapezoidal prism constructed by bonding together and integrating the first trapezoidal prism 131, the first right-angle prism 132, the second right-angle prism 133, the third right-angle prism 134, the second trapezoidal prism 135, and the fourth right-angle prism 136, and anti-reflection (AR) films 144, 145 are vapor-deposited on the top and bottom surfaces of the trapezoidal prism.

[0057] In the laser rangefinder 100, the first light source 110 emits S-polarized measurement light S1 via a reflective (polarization-preserving) collimator 111, and the second light source 120 emits S-polarized reference light S2 via a reflective (polarization-preserving) collimator 112. The S-polarized measurement light S1 and reference light S2 have their polarization directions adjusted via half-wavelength (λ / 2) plates 113 and 114, and are then incident on the prism unit 130.

[0058] The measurement light S1 and the reference light S2 incident on the prism unit 130 are incident on the polarizing beam splitter film 143 via one surface 133a of the two surfaces 133a and 133b forming a right angle of the second rectangular prism 133, and are split by the polarizing beam splitter film 143 into two measurement light S 1S ,S 1P and the reference beam S2S ,S 2P It is branched into.

[0059] The measurement light S of one polarized light reflected by the polarizing beam splitter film 143 1S is incident on the beam splitter film 142A, and the beam splitter film 142A splits the one polarized measuring light S 1S Two measuring beams S are used in a 1:1 ratio. 11 ,S 12 It is branched into.

[0060] The measurement light S is split into two beams at a ratio of 1:1 by the beam splitter film 142A. 11 ,S 12 is the measurement light S 11 is emitted through a surface 132a of the first rectangular prism 132 perpendicular to the optical path and enters the second photodetector 170, and the other measurement light S 12 is reflected by surface 131c functioning as total reflection surface 141A, bent by 90°, emitted via surface 131a perpendicular to the optical path of the first trapezoidal prism 131, and enters the second photodetector 170.

[0061] The other polarized measurement light S 1P is emitted from a surface 133a of the second rectangular prism 133 that is perpendicular to the optical path, and passes through a quarter-wave (λ / 4) plate 115 to be converted into circularly polarized measurement light S 1C The light is then incident on the measurement surface 150 .

[0062] The reflected light S perpendicularly reflected by the measurement surface 150 1C The reflected light S ′ of one polarized light is returned to the polarized beam splitter film 143 of the prism unit 130 via the quarter-wave (λ / 4) plate 115, and is reflected by the polarized beam splitter film 143 as a reflected light S 1S The reflected light S′ of one of the polarized lights is incident on the beam splitter film 142B, which splits the reflected light S 1S 'There are two reflected lights in a 1:1 ratio. 11 ',S12 ' is branched to.

[0063] The reflected light S is split into two beams at a ratio of 1:1 by the beam splitter film 142B. 11 ',S 12 ' is the reflected light S 11 The reflected light S′ is emitted through a surface 136a of the fourth rectangular prism 136 perpendicular to the optical path and enters the first photodetector 160. 12 The light ray ' is reflected by surface 135c functioning as total reflection surface 141B, bent by 90°, and emitted through surface 135a perpendicular to the optical path of the second trapezoidal prism 135, and enters the first photodetector 160.

[0064] Also, the reference light S 2S is reflected by the surface 135c of the second trapezoidal prism 135, which functions as the total reflection surface 141B, and is bent by 90 degrees to enter the beam splitter film 142A, and the one polarized reference light S 2S There are two reference beams S in a 1:1 ratio. 21 ,S 22 It is branched into.

[0065] The reference light S is split into two beams at a ratio of 1:1 by the beam splitter film 142A. 21 ,S 22 is the reference beam S 21 is emitted through surface 132a perpendicular to the optical path of the first right-angle prism 132 and enters the second photodetector 170, and the other reference light S2 is reflected by surface 131c functioning as the total reflection surface 141A, bent 90°, and emitted through surface 131a perpendicular to the optical path of the first trapezoidal prism 131 and enters the second photodetector 170.

[0066] The other polarized reference light S 2Pis emitted from a surface 133a of the second rectangular prism 133 that is perpendicular to the optical path, and passes through a quarter-wave (λ / 4) plate 116 to be converted into circularly polarized measurement light S 2C The light is then incident on the reference surface 155 .

[0067] The reflected light S perpendicularly reflected by the reference surface 155 2C The reflected light S ′ of one polarized light is returned to the polarized beam splitter film 143 of the prism unit 130 via the quarter-wave (λ / 4) plate 116, and is reflected by the polarized beam splitter film 143 as a reflected light S 2S The reflected light S′ of the one polarized light is reflected by the surface 135c of the second trapezoidal prism 135, which functions as the total reflection surface 141B, and is bent by 90° to enter the beam splitter film 142B. 2S 'There are two reflected lights in a 1:1 ratio. 21 ',S 22 ' is branched to.

[0068] The reflected light S is split into two beams at a ratio of 1:1 by the beam splitter film 142B. 21 ',S 22 ' is the reflected light S 21 The reflected light S′ is emitted through a surface 136a of the fourth rectangular prism 136 perpendicular to the optical path and enters the first photodetector 160. 22 ' is reflected by surface 135c functioning as total reflection surface 141B, bent by 90°, and emitted through surface 135a perpendicular to the optical path of the second trapezoidal prism 135, and enters the first photodetector 160.

[0069] The first photodetector 160 detects the reflected light S 1C ' and the reflected light S from the reference surface 155 2C The interference light of the reflected light S′ is detected by the beam splitter film 142B formed on the second trapezoidal prism 135 of the prism unit 130, which is superimposed on the reflected light S and split into two. 11 ',S 12 ' and reflected light S21 ',S 22 The interference light between the first and second light beams ' and ' is detected by two photodetectors 161A and 161B, and the difference between the detected light beams is detected by a differential detector 162.

[0070] The second photodetector 170 detects interference light between the measurement light S1 and the reference light S2, and detects the measurement light S1 and the reference light S2 that are superimposed and split into two by a beam splitter film 142A formed on the first trapezoidal prism 131 of the prism unit 130. 11 ,S 12 and the reference beam S 21 ,S 22 The interference light between these two beams is detected by two photodetectors 171A and 171B, and the difference between these beams is detected by a differential detector 172.

[0071] The signal processing unit 180 detects the time difference of an interference signal obtained by detecting the interference light between the measurement light S1 and the reference light S2 by the second photodetector 170, and detects the reflected light S from the measurement surface 150 by the first photodetector 160. 1C ' and the reflected light S from the reference surface 155 2C Based on the time difference of the interference signals obtained by detecting the interference light of ', a process is performed to obtain the speed of light, the refractive index at the measurement wavelength, and the difference between the distance to the reference surface 155 and the distance to the measurement surface 150 from the group refractive index.

[0072] In this laser distance meter 100, if the height of the prism unit 130, i.e., the trapezoidal prism, is taken as h, the optical distance that the measurement light S1 emitted from the first light source 110 propagates through the prism unit 130 until it is incident on the second photodetector 170 is expressed as follows: 11 2h, measurement light S 12 is 2.5h, and the optical distance that the measurement light S1 emitted from the first light source 110 propagates through the prism unit 130 until it is incident on the first photodetector 160 is 11 '3h, reflected light S 12 ' is 3.5h.

[0073] In contrast, the optical distance that the reference light S2 emitted from the second light source 120 propagates through the prism unit 130 until it is incident on the second photodetector 170 is 21 is 1.5h, and the reference light S 22 is 2h, and the optical distance that the reference light S2 emitted from the second light source 120 propagates through the prism unit 130 until it is incident on the first photodetector 160 is 21 ' is 2h, reflected light S 22 ' is 2.5h.

[0074] That is, in this laser distance meter 100, the difference in optical path experienced by the measurement light S1 and the reference light S2 within the prism unit 130 until the interference light is detected by the first and second photodetectors 160, 170 is equal to each other at 1h.

[0075] Therefore, in the laser range finder 100, as described above, the first and second light sources 110 and 120 are irradiated through the reflective (polarization-preserving) collimators 111 and 112. Diverging light The S-polarized measurement light S1 and reference light S2, which are converted into parallel light from the polarized light beam and enter the prism unit 130, have a light path that passes through air with little dispersion, so that group delay distribution is unlikely to occur in the beam cross section, and the light is entered into the prism unit 130 without a group velocity optical path difference.Even if the temperature of the prism unit 130 changes, the relative relationship between the interference lights detected by the first and second photodetectors 160, 170 remains constant, making it possible to perform high-precision optical interference observation without ghosts.

[0076] In addition, since this laser rangefinder 100 outputs the difference between the distance to the reference surface 155 and the distance to the measurement surface 150, by placing the measurement surface 150 and the reference surface 155 close to each other, the effect of changes in the refractive index of the atmosphere can be further reduced, thereby improving the measurement accuracy.

[0077] In this laser range finder 100, the polarizing beam splitter film 143 sandwiched between the inclined surfaces 133c, 134c of the second rectangular prism 133 and the third rectangular prism 134 can be replaced with a beam splitter film. In this case, although the optical loss increases, the 1 / 4 wavelength (λ / 4) plates 115, 116 become unnecessary.

[0078] Here, in the laser distance meter 100, the first and second light sources 110, 120 emit coherent measurement light S1 and reference light S2 whose intensity or phase is periodically modulated and whose modulation periods are different from each other, but the present invention can also be applied to a laser displacement meter, in which case an unmodulated wavelength-stabilized light source can be used for the reference light S2. In a laser displacement meter, the same light as the reference light is used for the measurement light, or light whose frequency is shifted from the reference light by a certain amount is used.

[0079] Even in this case, by using an interferometer equipped with an interferometer prism like the above-mentioned laser distance meter 100, the difference between the distance to the reference surface and the distance to the measurement surface is the difference in the actual optical path, which is an advantage.

[0080] That is, while a displacement meter only measures changes in distance, by using an interferometer equipped with the above-mentioned interferometer prism, the distance can be defined as 0 when the measurement surface and reference surface are aligned. Therefore, even when correcting for the refractive index fluctuation of the atmosphere, no unknown distance (dead path) occurs by defining the distance as 0 when the measurement surface and reference surface are aligned. This is not possible even if a normal interferometer is used as a displacement meter, because the reference light and measurement light are not emitted in the same direction.

[0081] As described above, the measurement light S1 and the reference light S2 are emitted from the first and second light sources 110 and 120 via the reflective (polarization-preserving) collimators 111 and 112. Diverging lightBy using the prism unit 130, in which the optical signal is converted from the laser beam into parallel light and incident on the prism unit 130 as an interference optical instrument, the signal processing unit 180 can obtain measurement values ​​such as displacement, distance, or distribution from the interference signal detected by the first photodetector 160 and the interference signal detected by the second photodetector 170. The differences in optical distance experienced within the prism unit 130 until the measurement light and the reference light are detected as interference lights by the first and second photodetectors 160, 170 are equal to each other, and even if the temperature of the prism unit 130 changes, the relative relationship between the interference lights detected by the first and second photodetectors is constant, making it possible to perform highly accurate optical interference observation without ghosts.

[0082] The present invention can be used, for example, as an interferometer for optical coherence tomography (OCT) other than the above-mentioned laser distance meter 100. By using an interferometer including the above-mentioned interferometer prism, it is possible to improve the accuracy of industrial applications of OCT.

[0083] When using an interferometer equipped with the above-mentioned interferometer prism for optical coherence tomography (OCT), light sources with different coherences are used for time domain OCT, spectral domain OCT, and Fourier domain OCT. In addition, in time domain OCT and spectral domain OCT, a white light source is used as the reference light, and light in which the reference light is branched and the relative delay time is adjusted is used as the measurement light. Furthermore, in Fourier domain OCT, a SS light source is used as the reference light, and light in which the reference light is branched and the relative delay time is adjusted is used as the measurement light. In addition, in spectral domain OCT, a spectrometer is used as the photodetector.

[0084] Here, in the above-mentioned laser distance meter 100 that calculates the distance to only one point, the interference signal detected by the second photodetector 170 plays a role in clarifying the reference plane.

[0085] When an interferometer including the above-described interferometer prism is applied to OCT, one of the interference signals detected by the two photodetectors not only serves to define the reference plane but also serves another purpose.

[0086] That is, in the case of OCT, an important application is to show the distribution of reflection points in the depth direction, but even if the light is reflected from a single point, when it is replaced with the distribution of reflection points with respect to distance (point spread function), the width of the distribution may be wider than the theoretical limit. This is due to the difference in dispersion of the medium that the measurement light and reference light have experienced before they interfere.

[0087] However, in an interferometer equipped with the above-mentioned interferometer prism, the interference signal detected by the first photodetector 160 and the interference signal detected by the second photodetector 170 experience the same medium dispersion, so by applying the above-mentioned interferometer prism to OCT, it becomes possible to calculate in real time the difference in medium dispersion experienced by the measurement light and the reference light from the interference signal detected by the second photodetector 170.

[0088] Furthermore, the results can be used to perform computations to correct for the variance of the interference signal detected by the first photodetector 160 in real time.

[0089] This makes it possible to obtain OCT images with higher clarity.

[0090] Here, in the laser distance meter 100, the prism unit 130 is used as an interference optical meter, and a measurement light S1 and a reference light S2 are emitted from the first and second light sources 110 and 120 via reflection type (polarization-preserving) collimators 111 and 112. Diverging lightThe present invention is not limited to the laser rangefinder 100, but uses a reflective optical system instead of a refractive optical system in order to eliminate the distribution of group delay in the cross section of the measurement light beam in an optical rangefinder that irradiates a measurement object with modulated light from a light-projecting unit, detects the modulated light reflected by the measurement object and returns, and calculates the distance to the measurement object by a signal processing unit from the time delay of the measurement signal obtained by detecting the modulated light reflected by the measurement object and returning. In this invention, a reflective optical system is provided in the light-projecting unit that irradiates the measurement object with modulated light, and by using the reflective optical system, the distribution of group delay in the cross section of the measurement light beam is eliminated, thereby eliminating measurement errors caused by the distribution of group delay in the cross section of the measurement light beam, and an optical rangefinder can be realized that measures and calculates the distance to the measurement object with high accuracy by the signal processing unit from the time delay of the measurement signal obtained by the light-receiving unit.

[0091] That is, the optical rangefinder of the present invention comprises a light-projecting unit consisting of a reflective optical system that irradiates a measurement object with light whose intensity or phase is periodically modulated as measurement light, an interference optical system that superimposes the light reflected by the measurement object from the measurement light irradiated to the measurement object via the light-projecting unit with a reference light whose intensity or phase is periodically modulated, a light-receiving unit that receives interference light between the measurement light and the reference light reflected and returned by the measurement object by the interference optical system, and a signal processing unit to which a measurement signal which is an interference signal obtained as a detection output of the interference light by the light-receiving unit is input, and the signal processing unit calculates the distance to the measurement object by analyzing based on the relative relationship between the measurement signal and a reference signal which is a signal that generates the measurement light or reference light or a signal generated by the measurement light or reference light.

[0092] The reflective optical system provided in the light-projecting unit is a reflective collimator that converts modulated light emitted into space from the light output end into parallel light, and the light output end can be a part that outputs light from a light source into space, or a part that outputs light into space at the end of an optical path extended from the light source by an optical waveguide such as an optical fiber.

[0093] The optical rangefinder of the present invention is an interference detection type optical rangefinder that uses multiple wavelengths for one distance measurement, such as a wavelength swept light source, a multi-wavelength light source, a white light source, or an optical comb light source, and can be, for example, as in the optical rangefinder 10 shown in Figure 4, a beam splitter 13 is provided as an interference optical system that separates modulated light S emitted as measurement light from a light source 11 via a light projecting unit 12 into reference light SR and measurement light SS, and irradiates the measurement light SS onto the object to be measured 1 and superimposes the reference light SS' that has passed through a reference optical path with the measurement light SS' that has been reflected by the object to be measured 1 and returned to obtain interference light.

[0094] This optical rangefinder 10 inputs modulated light S containing multiple wavelengths emitted into space from a light source 11, such as a wavelength swept light source, a multi-wavelength light source, a white light source, or an optical comb light source, into a beam splitter 13 as parallel modulated light S via a light projecting unit 12 consisting of a reflective (polarization-preserving) collimator, separates the parallel modulated light S into reference light SR and measurement light SS by the beam splitter 13, irradiates the reference light SR onto a reference surface 16 and irradiates the measurement light SS onto the object to be measured 1, and receives the interference light obtained by superimposing the reference light SR reflected and returned by the reference surface 16 and the measurement light SS reflected and returned by the object to be measured 1 via the beam splitter 13 at a light receiving unit 14, thereby detecting a measurement signal as an interference signal.

[0095] In this optical rangefinder 10, the beam splitter 13, which overlaps the reference light SR' reflected and returned by the reference surface 16 and the measurement light SS' reflected and returned by the object to be measured 1, separates the modulated light S emitted from the light source 11 via the light-projecting unit 12 as the measurement light SS into the reference light SR and the measurement light SS, and functions as an optical interference system that irradiates the object to be measured 1 with the measurement light SS' reflected and returned by the object to be measured 1, and obtains interference light by overlapping the reference light SR' reflected and returned by the reference surface 16, i.e., the reference light SR' that has passed through a round-trip optical path that includes the reference surface 16 that reflects the reference light SR as a reference optical path, and the measurement light SS.

[0096] In this optical rangefinder 10, the light-projecting section 12, which consists of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 11 into parallel measurement light SS, is less likely to cause a group delay distribution in the beam cross section and does not involve group velocity optical path difference.In the signal processing section 15, the interference signal obtained as the detection output of the interference light by the light-receiving section 14 is analyzed based on the relative relationship between the measurement signal by the measurement light SS reflected and returned by the object to be measured 1 and the reference signal, which is a signal that generates measurement light or reference light or a signal generated by the measurement light or reference light.The distance to the object to be measured 1 can be calculated with high accuracy from the time difference (phase difference) between the reference light SR reflected and returned by the reference surface 16 and the measurement light SS reflected and returned by the object to be measured 1.

[0097] Furthermore, in this optical rangefinder 10, as in the optical rangefinder 10A shown in Figure 5, a reflective focuser 17 that converts the interference light from parallel light to convergent light can be provided in the optical path along which the interference light is irradiated to the light-receiving unit 14, so that the interference light can be detected with high sensitivity by the light-receiving element of the light-receiving unit 14.

[0098] In addition, in this optical range finder 10A, the components other than the reflective focuser 17 are the same as those in the optical range finder 10 described above, so the same reference numerals are used in the drawing and detailed description thereof will be omitted.

[0099] Here, the reflective collimator constituting the light projecting section 12 and the reflective focuser 17 provided in the light receiving section 14 are of the same optical system in which the incident side and the exiting side are reversed to each other.

[0100] In this optical distance meter 10A, the light-projecting unit 12 consists of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 11 into parallel measurement light SS, and the reflective focuser 17 provided in the light-receiving unit 14 is less likely to cause a group delay distribution in the beam cross section and is not accompanied by a group velocity optical path difference.The interference light is detected with high sensitivity by the light-receiving element of the light-receiving unit 14, and the interference signal obtained as the detection output of the interference light by the light-receiving unit 14 in the signal processing unit 15 is analyzed based on the relative relationship between the measurement signal by the measurement light SS reflected and returned by the measurement object 1 and the reference signal which is a signal that generates measurement light or reference light or a signal generated by the measurement light or reference light, so that the distance to the measurement object 1 can be calculated with high accuracy from the time difference (phase difference) between the reference light SR reflected and returned by the reference surface 16 and the measurement light SS reflected and returned by the measurement object 1.

[0101] In addition, an optical rangefinder using an interference detection method may be, for example, an optical rangefinder 20 shown in Figure 6, which includes two light-projecting units 22S, 22R, each of which is a reflective optical system into which modulated light S emitted into space from a light source 21 is branched and incident, and an interference optical system 23 irradiates the modulated light S emitted from one of the light-projecting units 22S onto the object to be measured 1 as measurement light SS, and superimposes the measurement light SS' reflected and returned by the object to be measured 1 with the modulated light S emitted from the other light-projecting unit 22R as reference light SR to obtain interference light.

[0102] In this optical range finder 20, the reflection optical system provided in the two light projecting units 22S, 22R is a reflection collimator that converts the modulated light S radiated into space from the light source 21 and branched into parallel light.

[0103] In the interference optical system 23 in the optical range finder 20, modulated light S including a plurality of wavelengths emitted into space from the light source 21 is incident on a first beam splitter 23A as measurement light SS via a first light projecting unit 22S consisting of a reflective (polarization-preserving) collimator, and a portion of the modulated light S is separated and incident on a second beam splitter 23B as reference light SR via a second light projecting unit 22R consisting of a reflective (polarization-preserving) collimator, and the measurement light SS that has passed through the first beam splitter 23A is irradiated onto the measurement object 1. The measurement light SS' reflected and returned by the object to be measured 1 is reflected by the first beam splitter 23A and enters the second beam splitter 23B, and the measurement light SS' reflected and returned by the object to be measured 1 and the reference light SR are superimposed at the second beam splitter 23B to obtain interference light, and this interference light is received by the light receiving unit 24 to obtain an interference signal obtained as a detection output of the interference light by the light receiving unit 24.

[0104] The signal processing unit 25 analyzes the interference signal obtained as the detection output of the interference light by the light receiving unit 24 based on the relative relationship between the measurement signal generated by the measurement light SS reflected and returned by the object to be measured 1 and a reference signal which is a signal that generates measurement light or reference light or a signal generated by the measurement light or reference light, and can calculate the distance to the object to be measured 1 with high accuracy from the time difference (phase difference) between the reference light SR and the measurement light SS' reflected and returned by the object to be measured 1.

[0105] In this optical range finder 20, the light receiving unit 24 includes optical elements such as a detection element and a polarizer, which are necessary for obtaining an interference signal. In order to cause light to interfere, the light must be in the same polarization state. There are several methods for obtaining an interference signal, such as superimposing the measurement light and the reference light, extracting and detecting the same polarization component with a polarizer, or separating the light into two orthogonal polarization components with a polarizing beam splitter and detecting each with an independent photodetector, and obtaining an interference signal as the difference between the two signals. In addition, the light wavelength may be separated and detected by a wavelength dispersion element such as a diffraction grating, and the light receiving element is not limited to one detection element.

[0106] In this optical rangefinder 20, the first light-projecting unit 22S consists of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 21 into a parallel measurement light SS, and the second light-projecting unit 22R consists of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 21 into a parallel reference light SR. In this manner, a distribution of group delay is unlikely to occur in the beam cross section, and there is no group velocity optical path difference. In the signal processing unit 25, the interference signal obtained as the detection output of the interference light by the light-receiving unit 24 is analyzed based on the relative relationship between the measurement signal of the measurement light SS' reflected and returned by the object to be measured 1 and the signal that drives the light source 21, and the distance to the object to be measured 1 can be calculated with high accuracy from the time difference (phase difference) between the reference light SR and the measurement light SS' reflected and returned by the object to be measured 1.

[0107] In addition, in the optical rangefinder 20, as in the optical rangefinder 20A shown in Figure 7, a reflective focuser 27 that converts the interference light from parallel light to convergent light may be provided in the optical path along which the interference light is irradiated to the light-receiving unit 24, and the interference light may be made incident on the light-receiving element of the light-receiving unit 24 via the reflective focuser 27.

[0108] In addition, in this optical range finder 20A, the components other than the reflective focuser 27 are the same as those in the optical range finder 20 described above, so the same reference numerals are used in the drawing and detailed description thereof will be omitted.

[0109] The reflective collimator constituting the light projecting section 22 and the reflective focuser 27 provided in the light receiving section 24 are of the same optical system in which the incident side and the exiting side are reversed to each other.

[0110] In this optical rangefinder 20A, a first light-projecting unit 22S consisting of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 21 into a parallel measurement light SS, a second light-projecting unit 22R consisting of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 21 into a parallel reference light SR, and a reflective focuser 27 provided in the light-receiving unit 24 are configured such that a group delay distribution is unlikely to occur in the beam cross section and there is no group velocity optical path difference, and the interference light is detected with high sensitivity by the light-receiving element of the light-receiving unit 24, and the signal processing unit 25 analyzes the interference signal obtained as the detection output of the interference light by the light-receiving unit 24 based on the relative relationship between the measurement signal by the measurement light SS' reflected and returned by the measurement object 1 and the signal that drives the light source 21, thereby making it possible to calculate the distance to the measurement object 1 with high accuracy from the time difference (phase difference) between the reference light SR and the measurement light SS' reflected and returned by the measurement object 1.

[0111] Moreover, the interference detection type optical distance meter can also be configured as an optical distance meter 30 shown in FIG.

[0112] This optical rangefinder 30 comprises two light sources 31S, 31R that emit coherent modulated light into space, and two light-projecting units 32S, 32R, each consisting of a reflective optical system into which the modulated light S1, S2 emitted into space from the two light sources 31S, 31R is incident. The interference optical system 33 irradiates the modulated light S1 emitted from one of the light-projecting units 32S onto the measurement object 1 as measurement light SS, and superimposes the modulated light S2 emitted from the other light-projecting unit 32R as reference light SR on the measurement light SS' reflected and returned by the measurement object 1 to obtain interference light.

[0113] That is, the optical range finder 30 includes two light sources 31S and 31R that output measurement light and reference light whose intensity or phase is periodically modulated and whose modulation periods are different from each other, and the interference optical system 33 includes a first light source 31S and a first light projecting unit 32S that is made of a reflective (polarization-preserving) collimator, and modulated light S1 including a plurality of wavelengths that is emitted into space is incident on a first beam splitter 33A as measurement light S1, and a second light source 31R and a second light projecting unit 32R that is made of a reflective (polarization-preserving) collimator, and modulated light S2 including a plurality of wavelengths that is emitted into space is incident on a second beam splitter 33B as reference light SR. The measurement light SS is irradiated onto the object to be measured 1 and passes through the first beam splitter 33A, and the measurement light SS' reflected and returned by the object to be measured 1 is reflected by the first beam splitter 33A and enters the second beam splitter 33B, whereby the measurement light SS' reflected and returned by the object to be measured 1 and the reference light SR are superimposed at the second beam splitter 33B to obtain interference light by the interference optical system 33, and by receiving this interference light at the light receiving unit 34, an interference signal is obtained as a detection output of the interference light by the light receiving unit 34.

[0114] In this optical rangefinder 30, the first light-projecting unit 32S consists of a reflective (polarization-preserving) collimator that converts the modulated light S1 emitted into space from the first light source 31S into a parallel measurement light SS, and the second light-projecting unit 32R consists of a reflective (polarization-preserving) collimator that converts the modulated light S2 emitted into space from the second light source 31R into a parallel reference light SR. In this manner, a group delay distribution is unlikely to occur in the beam cross section, and there is no group velocity optical path difference. In the signal processing unit 35, the interference signal obtained as the detection output of the interference light by the light-receiving unit 34 is analyzed based on the relative relationship between the measurement signal by the measurement light SS reflected and returned by the object to be measured 1, and the reference signal which is a signal that generates the measurement light or reference light or a signal generated by the measurement light or reference light, and the distance to the object to be measured 1 can be calculated with high accuracy from the time difference (phase difference) between the reference light SR and the measurement light SS' reflected and returned by the object to be measured 1.

[0115] In this optical rangefinder 30, a reflective focuser that converts the interference light from parallel light to convergent light can be provided in the optical path along which the interference light is irradiated to the light-receiving unit 34, so that the interference light can be detected with high sensitivity by the light-receiving element of the light-receiving unit 34.

[0116] Moreover, the interference detection type optical distance meter can also be configured as an optical distance meter 40 shown in FIG.

[0117] The optical range finder 40 includes two light sources 41S and 41R that output measurement light and reference light whose intensity or phase is periodically modulated and whose modulation periods are different from each other.

[0118] In the interference optical system 43 of this optical rangefinder 40, modulated light S1 containing multiple wavelengths emitted into space from a first light source 41S is incident on a first beam splitter 43A as measurement light SS via a first light-projecting section 42S consisting of a reflective (polarization-preserving) collimator, and the measurement light SS is split into two by the first beam splitter 43A.One of the measurement lights SS is reflected by the first beam splitter 43A and bent 90 degrees to be incident on a second beam splitter 43B, while the other measurement light SS that passes through the first beam splitter 43A is irradiated onto the object to be measured 1.

[0119] In addition, modulated light S2 containing multiple wavelengths emitted into space from the second light source 41R is incident on the third beam splitter 43C as reference light SR via the second light-projecting section 42R consisting of a reflective (polarization-preserving) collimator, and the reference light SR is split into two by this third beam splitter 43C. One of the reference lights SR that passes through the third beam splitter 43C is incident on the fourth beam splitter 43D, and the other reference light SR that is reflected by the third beam splitter 43C and bent by 90 degrees is incident on the second beam splitter 43B.

[0120] The interference optical system 43 in this optical rangefinder 40 obtains reference interference light by superimposing the measurement light SS and the reference light SR in the second beam splitter 43B, and obtains a reference interference signal as a detection output of the reference interference light by the reference light receiving unit 44R by receiving this reference interference light by the reference light receiving unit 44R.

[0121] In addition, in the interference optical system 43 of this optical rangefinder 40, the measurement light SS that has passed through the first beam splitter 43A is irradiated onto the measurement object 1, and the measurement light SS' reflected by the measurement object 1 and returned is reflected by the first beam splitter 43A and enters the fourth beam splitter 43D, whereby the measurement light SS' and the reference light SR are superimposed at the fourth beam splitter 43D to obtain measurement interference light, and by receiving this measurement interference light at the measurement light receiving unit 44S, a measurement interference signal is obtained as a detection output of the measurement interference light by the measurement light receiving unit 44S.

[0122] In this optical rangefinder 40, the first light-projecting unit 42S consists of a reflective (polarization-preserving) collimator that converts the modulated light S1 emitted into space from the first light source 41S into parallel measurement light SS, and the second light-projecting unit 42R consists of a reflective (polarization-preserving) collimator that converts the modulated light S2 emitted into space from the second light source 41R into parallel reference light SR. In this manner, a distribution of group delay is unlikely to occur in the beam cross section, and no group velocity optical path difference occurs. In the signal processing unit 45, the distance to the object to be measured 1 can be calculated with high accuracy from the time difference (phase difference) between the reference interference signal obtained in the reference light detection unit 44R and the measurement interference signal obtained in the measurement light receiving unit 44S.

[0123] By providing a reflective focuser that converts the reference interference light received by the reference light detection unit 44R from parallel light to convergent light, and a reflective focuser that converts the measurement interference light received by the measurement light detection unit 44S from parallel light to convergent light, it is possible to detect the reference interference light with high sensitivity by the light receiving element of the reference light detection unit 44R and to detect the measurement interference light with high sensitivity by the light receiving element of the measurement light receiving unit 44S.

[0124] In the optical range finder 40, the first beam splitter 43A to the fourth beam splitter 43D and the total reflection mirror 43E constitute an interference optical system 43, which can be an interferometer prism having a structure in which a deposition film is formed on the surface of a trapezoidal prism or a right-angle prism by deposition and then bonded together to form an integrated structure. The laser range finder 100 shown in Fig. 1 described above is a specific example of an interference detection type optical range finder having an interferometer prism as the prism unit 130, which has an interferometer prism having a structure in which a beam splitter film or the like is formed on the surface of a trapezoidal prism or a right-angle prism by deposition and then bonded together to form an integrated structure.

[0125] In addition, a reflective collimator that converts modulated light emitted from a light source into space into parallel light and a reflective focuser that converts parallel light into converging light can also be applied to laser light emitted into space via an optical fiber.

[0126] That is, the interference detection type optical range finder can be configured as an optical range finder 50 shown in FIG.

[0127] The optical distance meter 50 includes a light source unit 51 including two optical comb light sources 51S and 51R that output a measurement light SS and a reference light SR whose intensity or phase is periodically modulated and whose modulation periods are different from each other; an optical fiber interferometer 52 in which the measurement light SS from the first optical comb light source 51S of the light source unit 51 is input to a first optical coupler 53A via an optical fiber, and the reference light SR from the second optical comb light source 51R is input to a second optical coupler 52B via an optical fiber; a measurement light detector 54S connected to a fourth optical coupler 53D of the optical fiber interferometer 52 via two optical fibers, a reference light detector 54R connected to a fifth optical coupler 53E of the optical fiber interferometer 53 via two optical fibers; a reflective optical system 56 connected to a third optical coupler 53C of the optical fiber interferometer 53 via an optical fiber; and an arithmetic processing unit 55 that calculates the distance to the measurement object 1 based on a measurement signal obtained by the measurement light detector 54S and a reference signal obtained by the reference light detector 54R.

[0128] The optical fiber interferometer 53 provided in this optical rangefinder 50 consists of five optical couplers 53A to 53E connected via optical fibers, the first optical coupler 52A into which the measurement light SS is incident is connected via optical fibers to a third optical coupler 53C and a fourth optical coupler 53D, the second optical coupler 52B into which the reference light SR is incident is connected via optical fibers to the fourth optical coupler 53D and a fifth optical coupler 53D, and the third optical coupler 53C is connected to the fifth optical coupler 53D via an optical fiber.

[0129] In the optical fiber interferometer 53, the measurement light SS incident on the first optical coupler 52A is radiated into space from a reflective optical system 56 connected to the third optical coupler 53C via an optical fiber and irradiated onto the object to be measured 1, and the measurement light SS' reflected by the object to be measured 1 and returning to the reflective optical system 56 is incident on a fifth optical coupler 53E connected to the third optical coupler 53C via an optical fiber.

[0130] The fifth optical coupler 53E is connected via an optical fiber to the second optical coupler 52B into which the reference light SR is incident, and therefore, in the fifth optical coupler 53E, the reference light SR incident on the second optical coupler 52B is superimposed on the measurement light SS' returning via the reflective optical system 56 to obtain measurement interference light.

[0131] When outputting the measurement interference light obtained by superimposing the reference light SR and the measurement light SS', the fifth optical coupler 53E switches the relationship between the reference light SR and the measurement light SS' arranged on the transmission side and the reflection side of the optical coupler, and outputs the light by splitting it into two.

[0132] The measurement light receiving unit 54S is a differential detector equipped with two photodetectors that receive two measurement interference lights in which the relationship between the reference light SR and the measurement light SS' is swapped by the fifth optical coupler 53E, and extracts a measurement interference signal from the difference between the two detection signals.

[0133] By receiving this measurement interference light by the measurement light receiving section 54S, a measurement interference signal can be obtained as a detection output of the measurement interference light by the measurement light receiving section 54S.

[0134] In the measurement light receiving section 54S, the difference between the two detection signals is calculated, thereby enabling the interference signal to be emphasized and the intensity noise to be suppressed, and the signal-to-noise ratio (S / N) of the measurement interference signal to be increased.

[0135] In addition, the fourth optical coupler 53D is connected via optical fibers to the first optical coupler 52A, into which the measurement light SS is incident, and to the second optical coupler 52B, into which the reference light SR is incident. Therefore, in the fourth optical coupler 53D, the measurement light SS incident on the first optical coupler 52A and the reference light SR incident on the second optical coupler 52B are superimposed to obtain reference interference light.

[0136] When outputting the reference interference light obtained by superimposing the measurement light SS, the reference light SR, and the measurement light SS, the fourth optical coupler 53D switches the relationship between the measurement light SS and the reference light SR arranged on the transmission side and the reflection side of the optical coupler, and outputs the light by splitting it into two.

[0137] The reference light receiving unit 54R is a differential detector equipped with two photodetectors that receive two reference interference lights in which the relationship between the reference light SR and the measurement light SS is swapped by the fourth optical coupler 53D, and extracts a reference interference signal from the difference between the two detection signals.

[0138] By receiving this reference interference light by the reference light receiving section 54R, a reference interference signal can be obtained as a detection output of the reference interference light by the reference light receiving section 54R.

[0139] In the reference light receiving section 54S, the difference between the two detection signals is calculated, thereby enabling the interference signal to be emphasized and the intensity noise to be suppressed, and the signal-to-noise ratio (S / N) of the reference interference signal to be increased.

[0140] Here, the reflective optical system 56 connected to the third optical coupler 53C via an optical fiber is a collimator that converts the measurement light SS irradiated to the object to be measured 1 into parallel light, a focuser that converts the measurement light SS' reflected by the object to be measured 1 and returned into convergent light, or an optical element such as a relay optical system provided between the optical fiber interferometers 53 and 53, which is composed of reflective optical elements.

[0141] In the reflective optical system 56 composed of reflective optical elements, a distribution of group delay is unlikely to occur in the beam cross section and there is no group velocity optical path difference, and in the signal processing unit 55, the distance to the measurement object 1 can be calculated with high accuracy from the time difference (phase difference) between the measurement interference signal obtained as a detection output by the measurement light receiving unit 54S which receives the measurement interference light obtained by the optical fiber interferometer 53, and the reference interference signal obtained as a detection output by the reference light receiving unit 54R which receives the reference interference light.

[0142] Here, the laser rangefinder 100 and each of the optical rangefinders 10 to 50 irradiate measurement light onto the object to be measured 1 and measure the distance to the object to be measured 1 based on the measurement light reflected and returned by the object to be measured 1. For example, as shown in FIG. 11, by providing an optical scanning device 81 that scans the object to be measured 1 with the measurement light irradiated onto the object to be measured 1, it functions as an optical three-dimensional shape measuring device 80 that measures the three-dimensional shape of the object to be measured 1 in a non-contact manner. In the laser range finder 100 and each of the optical range finders 10 to 50, the group delay distribution of the measurement light irradiated onto the measurement object 1 can be evaluated by an evaluation experiment system 300 shown in FIG. That is, in the laser rangefinder 100 and each of the optical rangefinders 10 to 50, the light-projecting section consisting of the reflective optical system irradiates a measurement light beam onto the center of a retroreflector via an optical chopper, and the group delay distribution has been evaluated by an evaluation experimental system that evaluates the group delay distribution on the cross section of the measurement light beam reflected by the retroreflector and returning via the optical chopper, thereby providing a high-quality optical rangefinder.

[0143] The optical three-dimensional shape measuring device 80 includes, for example, a laser distance meter 100 shown in FIG. C1 and a signal processing device 82 that measures absolute distances to a plurality of points on the object 1 based on the output of the laser distance meter 100 to obtain a three-dimensional image.

[0144] The laser rangefinder 100 uses measuring light S C1 is emitted into space, and the measurement light S C1 By scanning the measurement object 1 with the C1 ', the absolute distance to the object 1 to be measured is measured.

[0145] The optical scanning device 81 detects the measurement light S emitted from the laser range finder 100. C1 The measuring object 1 is scanned with a reflective scanning optical system.

[0146] That is, in this optical three-dimensional shape measuring device 80, the measuring light S emitted from the laser range finder 100 C1 is irradiated from the optical scanning device 81 toward the measurement object 1, and reflected light S C1 ' returns to the laser range finder 100, and the absolute distance to the object surface is measured by the laser range finder 100.

[0147] The signal processing device 82 controls the optical scanning device 81 to scan the laser beam while acquiring absolute distance information to the surface of the object 1 measured by the laser rangefinder 100, and measures the three-dimensional shape of the object non-contact by accumulating the beam irradiation position and the absolute distance to that location for multiple points.

[0148] In this optical three-dimensional shape measuring device 80 as well, the optical scanning device 81 includes a reflective scanning optical system that scans the measurement object 1, so that the measurement light S C1 and reflected light S C1 Since group delay distribution is unlikely to occur in the beam cross section of ' and there is no group velocity optical path difference, the laser rangefinder 100 can measure the absolute distance to the surface of the object to be measured 1 with high accuracy, and the signal processing device 82 can measure the three-dimensional shape of the object without contact by acquiring absolute distance information to the surface of the object to be measured 1 measured by the laser rangefinder 100 and accumulating the beam irradiation position and the absolute distance to that location for a plurality of points. [Explanation of symbols]

[0149] 1 Measurement object, 10, 10A, 20, 20A, 30, 40, 50 Optical distance meter, 11, 21, 31S, 31R, 41S, 41R, 110, 120 Light source, 12, 22S, 22R, 32S, 32R, 42S, 42R Light projecting unit, 13, 23A, 23B, 33A, 33B, 43A to 43D Beam splitter, 14, 24, 34, 44 Light receiving unit, 15, 25, 35, 45, 55, 180 Signal processing unit, 33, 43 Interference optical system, 17, 27 Reflection type focuser, 44S Measurement light receiving unit, 44R Reference light detection unit, 16, 155 Reference surface, 43E Total reflection mirror, 51 Light source unit, 51S, 51R Optical comb light source, 52 Optical fiber interferometer, 53A to 53E Optical coupler, 54S Measurement light detector, 54R Reference light detector, 80 Optical three-dimensional shape measuring device, 81 Optical scanning device, 82 Signal processing device, 100 Laser distance meter, 111, 112 Reflection type collimator, 111a, 112a Parabolic mirror, 113, 114 1 / 2 wavelength (λ / 2) plate, 115, 116 1 / 4 wavelength (λ / 4) plate, 130 Prism unit, 150 Measurement surface, 160, 170 Photodetector, 161A, 161B, 171A, 171B Photodetector, 162, 172 Differential detector

Claims

1. A light projection unit comprising a reflection optical system that irradiates a measurement object with light whose intensity or phase is periodically modulated as measurement light; an interference optical system that superimposes light reflected by the measurement object out of the measurement light irradiated onto the measurement object via the light projecting unit and a reference light whose intensity or phase is periodically modulated; a reflective scanning optical system that scans a measurement object with the measurement light emitted from the light projecting unit; a light receiving unit that receives interference light between the measurement light and the reference light, which is obtained by the interference optical system and is reflected by the measurement object and returned via the reflective scanning optical system; a signal processing unit which receives a measurement signal, which is an interference signal obtained as a detection output of the interference light by the light receiving unit, and calculates a distance to the measurement object by analyzing the measurement signal based on a relative relationship between the measurement signal and a reference signal, which is a signal that generates the measurement light or reference light or a signal that is generated by the measurement light or reference light, and measures absolute distances to a plurality of points on the measurement object to obtain a stereoscopic image; Equipped with The optical rangefinder is characterized in that the interference optical system causes interference light between the measurement light and the reference light, which is reflected by the object to be measured and returned via the reflective scanning optical system, to be incident on the light receiving section.

2. The optical rangefinder described in Claim 1, characterized in that the light-projecting section consisting of the reflective optical system irradiates a measurement light beam onto the center of a retroreflector via an optical chopper, and the group delay distribution has been evaluated by an evaluation experimental system that evaluates the distribution of group delay at the cross section of the measurement light beam reflected by the retroreflector and returning via the optical chopper.

3. The reflection optical system provided in the light projection unit is a reflection collimator that converts modulated light emitted from the light output end into a space into parallel light, 3. The optical rangefinder according to claim 2, wherein the optical output end is a part that outputs light from a light source into space or a part that outputs light into space at the end of an optical path extended from a light source by an optical waveguide.

4. The optical rangefinder described in claim 3, characterized in that the reflective optical system includes a reflective collimator in the light-projecting section that converts modulated light into parallel light, and a reflective focuser in the light-receiving section that converts the interference light obtained by the interference optical system into convergent light and makes it incident on the light-receiving element.

5. The optical distance meter according to any one of claims 1 to 3, characterized in that the interference optical system separates modulated light emitted from the light source through the light-projecting unit as measurement light into reference light and measurement light, irradiates the reference light that has passed through a reference optical path and the measurement light onto the object to be measured, and superimposes the measurement light that has been reflected by the object to be measured and returned to obtain interference light.

6. 5. An optical distance meter as claimed in any one of claims 1 to 4, further comprising two light-projecting units, each consisting of a reflective optical system into which modulated light emitted from the optical output end into space is branched and incident, and the interference optical system irradiates the modulated light emitted from one of the light-projecting units onto the object to be measured as measurement light, and superimposes the measurement light reflected and returned by the object to be measured with the modulated light emitted from the other light-projecting unit as a reference light to obtain interference light.

7. 6. The optical distance meter according to claim 5, further comprising two light-projecting units, each consisting of a reflective optical system, into which modulated light emitted from the optical output end into space is branched and incident, and the interference optical system irradiates the modulated light emitted from one of the light-projecting units onto the object to be measured as measurement light, and superimposes the measurement light reflected and returned by the object to be measured with the modulated light emitted from the other light-projecting unit and passed through the reference optical path as reference light to obtain interference light.

8. 5. An optical distance meter as claimed in any one of claims 1 to 4, comprising two light sources that radiate mutually coherent modulated light into space, and two light-projecting units, each consisting of a reflective optical system into which the modulated light radiated into space from the two light sources is incident, wherein the interference optical system irradiates the modulated light emitted from one of the light-projecting units as measurement light onto the object to be measured, and superimposes the measurement light reflected and returned by the object to be measured with the modulated light emitted from the other light-projecting unit as a reference light to obtain interference light.

9. 9. The optical distance meter according to claim 8, further comprising a reference light receiving unit that receives reference interference light obtained by superimposing the modulated light emitted from the one light-projecting unit as measurement light and the modulated light emitted from the other light-projecting unit as reference light, wherein the interference optical system superimposes the modulated light emitted from the other light-projecting unit as reference light on the measurement light reflected and returned by the object to be measured to obtain measurement interference light, and causes the measurement interference light to be incident on the light receiving unit, and also obtains reference interference light obtained by superimposing the modulated light emitted from the one light-projecting unit as measurement light and the modulated light emitted from the other light-projecting unit as reference light, and causes the reference interference light to be incident on the reference light receiving unit, and the signal processing unit calculates a distance to the object to be measured from a time difference between a measurement signal obtained as a detection output of the measurement interference light by the light receiving unit and a reference signal obtained as a detection output of the reference interference light by the reference light receiving unit.

10. 10. The optical rangefinder according to claim 9, wherein the reference light receiving unit includes a reflective focuser that converts the reference interference light obtained by the interference optical system into convergent light and causes it to be incident on a light receiving element.

11. The optical distance meter according to claim 9, characterized in that the two light sources are optical comb light sources that output measurement light and reference light whose intensity or phase is periodically modulated and whose modulation periods are different from each other, and the interference optical system is an optical comb interferometer.

12. The optical distance meter according to claim 11, characterized in that the optical comb interferometer is a fiber-optic comb interferometer, and is provided with a reflective optical system that irradiates the measurement object with measurement light emitted into space via the fiber-optic comb interferometer, and causes the measurement light reflected by the measurement object and returned to be incident on the fiber-optic comb interferometer.

13. An evaluation method for evaluating the group delay distribution of measurement light emitted from the light-projecting unit of an optical rangefinder, characterized in that a measurement light beam is irradiated to the center of a retroreflector via an optical chopper, and the group delay distribution is evaluated at the cross section of the measurement light beam reflected by the retroreflector and returning via the optical chopper.

Images