JP7624738B2 - Optical range finder and evaluation method thereof - Google Patents

Description

The present invention relates to an optical distance meter and an evaluation method thereof, in which a light-projecting unit projects modulated light onto a measurement object, and a light-receiving unit detects the modulated light reflected by the measurement object and returns to the measurement object. The measurement signal thus obtained is then used to calculate the distance to the measurement object from the time delay of the measurement signal.

Distance measurement based on optical principles using laser light has been known as an active distance measurement method that can measure 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 is calculated based on the difference between the time the laser light is emitted and the time the laser light reflected from the target 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 is received using 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.

The present inventors have previously proposed a rangefinder with the configuration shown in FIG. 12 as a rangefinder capable of measuring long distances with high accuracy and in a short time (see, for example, Patent Document 1).

The laser distance meter 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 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, ₂ , a second photodetector 270 which detects interference light between the reflected light of the measurement light and the reflected light of the reference light, which are incident on the measurement surface 250 and the reference surface 255 and are superimposed via the prism unit 230, 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 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 a time difference between the interference signal detected by the first photodetector 260 and the interference signal detected by the second photodetector 270.

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.

The first photodetector 260 detects the interference light between the measurement light S1 and the reference light S2, and detects the interference light between the measurement light _S11 , _S12 and the reference light S21, _S22 , which are superimposed and split into two by the beam splitter film 242A formed on the first trapezoidal prism 231 of the prism unit ₂₃₀ , by two photodetectors 261A, 261B, and detects the difference between them by a differential detector 262.

In addition, the second photodetector 270 detects the interference light between the reflected light S _1C ' from the measurement surface 250 and the reflected light S _2C ' from the reference surface 255, and detects the interference lights between the reflected lights S ₁₁ ', S ₁₂ ' and the reflected lights S ₂₁ ', S ₂₂ ' which are superimposed and split into two by the beam splitter film 242B formed on the second trapezoidal prism 235 of the prism unit 230 by two photodetectors 271A, 271B, and the difference between them is detected by a differential detector 272.

The signal processing unit 280 performs processing to determine the 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 interference signals obtained by detecting the interference light between the measurement light _S1 and the reference light S2 using the first photodetector 260, and the time difference between interference signals obtained by detecting the interference light between the reflected light _S1C ' from the measurement surface 250 and the reflected light S2C' from the reference surface 255 using the second photodetector 270.

In this laser rangefinder 200, the difference in optical distance experienced within the prism unit 230 until the measurement light _S1 and reference light _S2 are detected as each interference light in 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 in 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.

Patent No. 5588769

Conventionally, optical distance meters that irradiate a measurement object with modulated light from a light-projecting unit, detect the modulated light reflected by the measurement object and return to the measurement object with a light-receiving unit, and use a signal processing unit to calculate the distance to the measurement object from the time delay of the measurement signal obtained by the detection. In these optical systems, refractive optical systems using 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 have been used.

The inventors of this invention have investigated how the difference in group velocity optical path difference distance experienced by a propagating laser light beam as it passes through a refractive optical system affects optical distance measurement distortion in an optical distance meter.

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

As shown in Figure 13, for a collimator lens made of 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 phase velocity and group velocity. The distribution of phase velocity distance and group velocity distance measured from focal position A within the beam is as 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.

That is, the beam that passes through the collimator lens has a constant phase velocity distance and becomes an equiphase plane within the parallel beam, as shown in Figure 15.

Here, if the wavelength is λ and the frequency is f, the wave number k is expressed as k = 2π/λ, the angular frequency ω is expressed as ω = 2πf, the phase velocity _vp , which is the speed at which one wave travels at a point where the phase is equal, is expressed as _vp = ω/k, and the group velocity _vg, which is the speed at which two waves travel at a point where the phase difference is equal, is expressed as _vg = dω/dk. In a vacuum, the phase velocity _vp and the group velocity _vg are equal. Also, the speed at which the pulse waveform of the optical comb travels is the group velocity _vg .

Assuming that the speed of light in a vacuum is c, the phase velocity _vp in a medium with a refractive index n is expressed as _vp = c/n, and the angular frequency ω is expressed as ω = ck = 2πc/λ. Furthermore, the group velocity _vg is expressed as _vg = c/ _ng , where _ng is the group refractive index and is expressed as _ng = c/ _vg .

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

On the other hand, the point where the phase difference is equal, that is, the time taken for the envelope of the pulse waveform to propagate, is represented by _τg in the following equation, which includes the wavelength dependency of the refractive index.
τ _g =L/v _g =n _g L/c=L(n-λdn/dλ)/c

In this way, since the time _τg during which the envelope of the pulse waveform propagates includes a term of the wavelength dependency of the refractive index, there is a time difference between the time τ during which the equiphase front propagates and the time τg during which the _envelope of the pulse waveform propagates.

Since the group velocity _vg is approximately 1 to 2% slower than the phase velocity _vp , and the peripheral part of the lens passes through the lens faster than the center of the lens depending on the optical path difference passing through the glass material, the outer light travels ahead. When evaluation was performed using an evaluation experimental system 300 configured as shown in FIG. 16, when laser light with a mode field diameter (MFD) of 3.5 mm passes through a lens, there is a distance difference of approximately 3 μm between the center position of the laser light beam and the outer position where the power density is attenuated to 1/ ^e2 based on the power density at the center of the beam.

In the evaluation experiment system 300, the measurement light beam from the range finder head 301 is irradiated to the center of the retroreflector 304 via the adjustment mirrors 302A and 302B and the optical chopper 303. The measurement light beam is reflected by the retroreflector 304 and returns to the range finder head 301. The optical chopper 303 blocks the measurement light beam from one side on the outward and return paths, 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 all the beam returns, the beam is gradually cut from both sides, with the center of the beam remaining until the end (states 1 to 5). When the beam leaves the blades of the optical chopper, the beam is restored from the center of the beam (states 5 to 9). This process is repeated.

In the evaluation experimental system 300, the distance to the retroreflector 304 was repeatedly measured, and the results are shown in Figure 18. As the measurement light beam returning to the range finder head 301 changes from state 0 to state 9, a downward convex distance fluctuation occurs, and in the center of the measurable section, the entire beam is used for measurement, including the peripheral beam, resulting in a shorter distance, 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.

In this way, it was found that in optical distance meters, if there is a distribution of group delay 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 portion of the beam cross section is detected, a distance error of several μm may occur compared to when the entire beam is detected with a mirror or retroreflector.

The present invention was devised in consideration of the above-mentioned problems of the conventional technology, and its purpose is to enable highly accurate distance measurement in an optical range finder 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.

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

Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of the embodiments described below.

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

That is, the present invention is an optical range finder, comprising: a light- projecting unit consisting of a reflection optical system that irradiates a measurement object with light whose intensity or phase is periodically modulated as measurement light; a reflection scanning optical system that scans the measurement object with the measurement light emitted from the light-projecting unit; an interference optical system that superimposes the measurement light, which is among the measurement light irradiated from the light-projecting unit through the reflection scanning optical system to the measurement object and is reflected by the measurement object and returned from the reflection scanning optical system through the light-projecting unit, on 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 that is reflected by the measurement object and returned by the measurement object, obtained by the interference optical system; and and a signal processing unit to which a measurement signal, which is an interference signal obtained as a detection output of the above-mentioned, is input, wherein the interference optical system causes 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 via the light projecting unit, to be incident on the light receiving unit, among the measurement light irradiated from the light projecting unit to the measurement object via the reflective scanning optical system, and the signal processing unit calculates the distance to the measurement object by analyzing the measurement signal 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 , and measures absolute distances to multiple points on the measurement object to obtain a stereoscopic image .
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.

In the optical rangefinder according to the present invention, the reflective optical system provided in the light projecting section is a reflective collimator that converts modulated light emitted from the light output end into space 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.

The optical rangefinder according to the present invention may further include, as the reflective optical system, 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.

The optical range finder according to the present invention also includes a reflective scanning optical system that scans the measurement object with the measurement light emitted from the light projecting unit, and the interference optical system can cause interference light between the measurement light and the reference light that is reflected by the measurement object and returned via the scanning optical system to be incident on the light receiving unit.

In addition, in the optical range finder according to the present invention, the interference optical system can separate modulated light emitted as measurement light from the light source via the light projector into reference light and measurement light, irradiate the reference light that has passed through a reference optical path with the measurement light that has been reflected by the measurement object and returned, and superimpose the measurement light to obtain interference light.

The optical rangefinder according to the present invention also includes two light-projecting units, each consisting of a reflection optical system, into which the modulated light emitted from the optical output terminal into space is branched and incident, and 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 back by the object to be measured and the modulated light emitted from the other light-projecting unit as reference light to obtain interference light.

The optical rangefinder according to the present invention also includes two light sources that emit coherent modulated light into space, and two light-projecting units, each consisting of a reflection optical system into which the modulated light emitted into space from the two light sources is incident. The interference optical system irradiates the measured object with the modulated light emitted from one of the light-projecting units as measurement light, and superimposes the measured light reflected back by the measured object with the modulated light emitted from the other light-projecting unit as reference light to obtain interference light.

The optical rangefinder according to the present invention also includes two light-projecting sections, each of which is a reflection optical system into which the 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 sections as measurement light onto the object to be measured, and superimposes the measurement light reflected back 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.

The optical distance meter according to the present invention further includes a reference light receiving unit that receives reference interference light obtained by superimposing the modulated light emitted from one of the light projectors as measurement light and the modulated light emitted from the other light projector as reference light, and the interference optical system superimposes the modulated light emitted from the other light projector as reference light on the measurement light reflected and returned by the object to be measured to obtain measurement interference light, which is incident on the light receiving unit, and also obtains reference interference light obtained by superimposing the modulated light emitted from one of the light projectors as measurement light and the modulated light emitted from the other light projector as reference light, which is 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 the measurement signal obtained as the detection output of the measurement interference light by the light receiving unit and the reference signal obtained as the detection output of the reference interference light by the reference light receiving unit.

In addition, in the optical rangefinder according to the present invention, the reference light receiving unit can 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.

In the optical range finder according to the present invention, 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 can be an optical comb interferometer.

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.
The present invention also provides a method for evaluating the group delay distribution of measurement light emitted from a light-projecting unit of an optical rangefinder, 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 reflected by the retroreflector and returning via the optical chopper .

In the optical rangefinder of the present invention, unlike refractive optics using optical lenses, the light path passes through air with little dispersion, and instead of refractive optics, a reflective optics using mirrors with flat, concave, or convex surfaces, which are less likely to produce a group delay distribution in the beam cross section, is used. This eliminates measurement errors caused by the distribution of group delay in the cross section of the measurement light beam, and allows for highly accurate distance measurements.

In addition, the optical rangefinder of the present invention can eliminate measurement errors caused by the distribution of group delay in the cross section of the measurement light beam, making it possible to measure the same distance by detecting only a portion of the beam area as when the entire beam is detected.

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.

FIG. 1 is a schematic diagram showing a configuration of a laser range finder to which the present invention is applied. 4 is a cross-sectional view showing the structure of a reflective collimator constituting a light projecting unit of the laser rangefinder. FIG. FIG. 2 is a plan view illustrating a schematic configuration of a prism unit provided in the laser rangefinder. FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. FIG. 13 is a schematic diagram showing another example of the configuration of an optical range finder to which the present invention is applied. FIG. 13 is a schematic diagram showing another example of the configuration of an optical rangefinder to which the present invention is applied. FIG. 13 is a schematic diagram showing still another configuration example of the optical range finder to which the present invention is applied. 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; FIG. 1 is a schematic diagram showing a configuration of a laser range finder proposed by the present inventors. 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. 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. FIG. 2 is a diagram showing an equiphase surface of a beam that has passed through the collimator lens. 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. 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. FIG. 11 is a diagram showing the results of repeatedly measuring the distance to a retroreflector in the above evaluation experiment system.

The following describes in detail the embodiments of the present invention with reference to the drawings. Common components are 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 spirit of the present invention.

The present invention is applied to a laser rangefinder 100 having a configuration such as that shown in FIG.

This laser rangefinder 100 is an application of the present invention to the laser rangefinder proposed in the previously-mentioned Patent Document 1, and includes 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 and 114.

That is, the laser distance meter 100 includes a first light source 110 which emits a measurement light _S1 , a second light source 120 which emits a reference light _S2 , a prism unit 130 into 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 into 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 and incident, and the measurement light _S1 and the reference light S2 are incident via the prism unit 130. ₂ , a second photodetector 170 which detects interference light between the reflected light of the measurement light and the reflected light of the reference light, which are incident on the measurement surface 150 and the reference surface 155 and are 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, based on the time difference between the interference signal detected by the first photodetector 160 and the interference signal detected by the second photodetector 170.

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. ... modulation periods are different from each other. The first and second light sources 110, 120 each emit a coherent measurement light _S1 and a reference light _S2 .

The reflective (polarization-preserving) collimators 111, 112 are reflective optical elements that function as light projecting sections that convert the S-polarized measurement light _S1 and reference light _S2 emitted into space from the first and second light sources 110, 120 from divergent light to parallel light, and are composed of parabolic mirrors 111a, 112a as shown in FIG. 2, for example. Unlike a refractive optical system that uses optical lenses, the light path passes through air with little dispersion, so that group delay distribution is less likely to occur in the beam cross section.

In this laser rangefinder 100, the S-polarized measurement light S1 and reference light S2 are converted from divergent light to parallel light from the first and second light sources ₁₁₀ , 120 via reflective (polarization-preserving) collimators 111, ₁₁₂ and then incident on the prism unit 130.Since the light path passes through air, which has little dispersion, the beam cross section is unlikely to have a distribution of group delay, and the light is incident on the prism unit 130 without a group velocity optical path difference.

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.

In this laser distance meter 100, the prism unit 130 includes a first trapezoidal prism 131 having two surfaces 131a and 131b that are perpendicular to the optical path and perpendicular to each other, and two surfaces 131c and 131d that are parallel to each other and are at 45° to the optical path, with a beam splitter film 142A formed on one surface, and 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, sandwiching the beam splitter film 142A, and a polarizing beam splitter film 143 formed on one of the inclined surfaces, and the polarizing beam splitter film 143 is formed on the polarizing beam splitter film 142A. The device is equipped with a second right-angle prism 133 and a third right-angle prism 134 in which the inclined surfaces 133c and 134c are bonded together with a beam splitter film 143 in between, a second trapezoidal prism 135 having two faces 135a and 135b that are perpendicular to the optical path and perpendicular to each other, and two faces 135c and 135d that are parallel to each other and are at 45° to the optical path, with a beam splitter film 142B formed on one face, and a fourth right-angle prism 136 in which the 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.

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

In the prism unit 130, one of the two surfaces 131a and 131b that are perpendicular to the optical path of the first trapezoidal prism 131 and one of the two surfaces 132a and 132b that are perpendicular to the optical path of the first rectangular prism 132 are attached to one of the two surfaces that are perpendicular to the optical path of the first rectangular prism 132 so that the beam splitter film 142A and the polarizing beam splitter film 143 are perpendicular to each other. At the same time, one of the two faces 132a, 132b that are perpendicular to the optical path of the second trapezoidal prism 135 and one of the two faces 136a, 136b that are perpendicular to the optical path of the fourth rectangular prism 136 are bonded to one of the two faces that are perpendicular to the second rectangular prism 133 so that the beam splitter film 142B and the polarizing beam splitter film 143 are parallel to each other.

The prism unit 130 is a trapezoidal prism formed by bonding together 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.

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.

The measurement light _S1 and 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 perpendicular surfaces 133a, 133b of the second rectangular prism 133, and are split by the polarizing beam splitter film 143 into two measurement light beams _S1S , _S1P and reference light beams _S2S , _S2P, respectively.

The measuring light S _1S of one polarized light reflected by the polarizing beam splitter film 143 is incident on the beam splitter film 142A, which splits the measuring light S _1S of one polarized light into two measuring light S ₁₁ and S ₁₂ at a ratio of 1:1.

Of the measurement beams _S11 and _S12 split into two at a 1:1 ratio by the beam splitter film 142A, one measurement beam _S11 is emitted through the surface 132a perpendicular to the optical path of the first rectangular prism 132 and enters the second photodetector 170, and the other measurement beam _S12 is reflected by the surface 131c functioning as the total reflection surface 141A, bent 90°, and emitted through the surface 131a perpendicular to the optical path of the first trapezoidal prism 131 and enters the second photodetector 170.

The other polarized measuring light _S1P transmitted through the polarizing beam splitter film 143 is emitted from a surface 133a of the second rectangular prism 133 that is perpendicular to the optical path, and is converted into a circularly polarized measuring light _S1C via a quarter-wavelength (λ/4) plate 115, which is then irradiated onto the measurement surface 150.

The reflected light S _1C ' reflected vertically by the measurement surface 150 is returned to the polarizing beam splitter film 143 of the prism unit 130 via the quarter-wavelength (λ/4) plate 115, and the reflected light S _1S ' of one polarized light reflected by the polarizing beam splitter film 143 is incident on the beam splitter film 142B, which splits the reflected light S _1S ' of one polarized light into two reflected lights S ₁₁ ', S ₁₂ ' in a 1:1 ratio.

Of the reflected light _S11 ', _S12 ' split into two at a 1:1 ratio by the beam splitter film 142B, one reflected light _S11 ' is emitted through surface 136a perpendicular to the optical path of the fourth right-angle prism 136 and enters the first photodetector 160, and the other reflected light _S12 ' is reflected by surface 135c functioning as the total reflection surface 141B, bent 90 degrees, and emitted through surface 135a perpendicular to the optical path of the second trapezoidal prism 135 and enters the first photodetector 160.

In addition, one of the polarized reference beams _S2S reflected by the polarizing beam splitter film 143 is reflected by the surface 135c functioning as the total reflection surface 141B of the second trapezoidal prism 135, bent 90 degrees, and incident on the beam splitter film 142A, and the one of the polarized reference beams _S2S is split into two reference beams _S21 , _S22 in a 1:1 ratio by this beam splitter film 142A.

Of the reference beams _S21 and _S22 split into two at a ratio of 1:1 by the beam splitter film 142A, one reference beam _S21 is emitted through the surface 132a perpendicular to the optical path of the first rectangular prism 132 and enters the second photodetector 170, and the other reference beam _S2 is reflected by the surface 131c functioning as the total reflection surface 141A, bent by 90°, and emitted through the surface 131a perpendicular to the optical path of the first trapezoidal prism 131 and enters the second photodetector 170.

The other polarized reference light _S2P that has passed through the polarizing beam splitter film 143 is emitted from the surface 133a of the second rectangular prism 133 that is perpendicular to the optical path, and passes through the quarter-wavelength (λ/4) plate 116 to become circularly polarized measurement light _{S2C, which} is then irradiated onto the reference surface 155.

The reflected light S _2C ' reflected vertically by the reference surface 155 is returned to the polarizing beam splitter film 143 of the prism unit 130 via the quarter-wavelength (λ/4) plate 116, and the reflected light S _2S ' of one polarized light reflected by the polarizing beam splitter film 143 is reflected by the surface 135c that functions as the total reflection surface 141B of the second trapezoidal prism 135, bent 90 degrees, and incident on the beam splitter film 142B, and the reflected light S _2S ' of one polarized light is split into two reflected lights S ₂₁ ', S ₂₂ ' in a 1:1 ratio by this beam splitter film 142B.

Of the reflected light _S21 ', _S22 ' split into two at a 1:1 ratio by the beam splitter film 142B, one reflected light _S21 ' is emitted through surface 136a perpendicular to the optical path of the fourth right-angle prism 136 and enters the first photodetector 160, and the other reflected light _S22 ' is reflected by surface 135c functioning as the total reflection surface 141B, bent 90°, and emitted through surface 135a perpendicular to the optical path of the second trapezoidal prism 135 and enters the first photodetector 160.

In addition, the first photodetector 160 detects the interference light between the reflected light S _1C ' from the measurement surface 150 and the reflected light S _2C ' from the reference surface 155, and detects the interference lights of the reflected lights S ₁₁ ', S ₁₂ ' and the reflected lights S ₂₁ ', S ₂₂ ' which are superimposed and split into two by the beam splitter film 142B formed on the second trapezoidal prism 135 of the prism unit 130 by two photodetectors 161A, 161B, and the difference between them is detected by a differential detector 162.

The second photodetector 170 detects the interference light between the measurement light _S1 and the reference light _S2 , and detects the interference light between the measurement light _S11 , _S12 and the reference light S21, _S22 , which are superimposed and split into two by the beam splitter film 142A formed on the first trapezoidal prism 131 of the prism unit ₁₃₀ , by two photodetectors 171A, 171B, and detects the difference between them by a differential detector 172.

The signal processing unit 180 performs processing to determine 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, based on the time difference between the interference signals obtained by detecting the interference light between the measurement light _S1 and the reference light _S2 by the second photodetector 170, and the time difference between the interference signals obtained by detecting the interference light between the reflected light S1C' from the measurement surface 150 and the reflected light S2C' from the reference surface 155 by the first photodetector 160.

In this laser rangefinder 100, if the height of the prism unit 130, i.e., the trapezoidal prism, is h, the optical distance that the measurement light _S1 emitted from the first light source 110 travels within the prism unit 130 from when it enters the prism unit 130 until it enters the second photodetector 170 is 2h for measurement light _S11 and 2.5h for measurement light _S12 , and the optical distance that the measurement light _S1 emitted from the first light source 110 travels within the prism unit 130 from when it enters the prism unit 130 until it enters the first photodetector 160 is 3h for reflected light _S11 ' and 3.5h for reflected light _S12 '.

In contrast, the optical distance that the reference light _S2 emitted from the second light source 120 travels within the prism unit 130 from when it enters the prism unit 130 until it enters the second photodetector 170 is 1.5h for reference light _S21 and 2h for reference light _S22 , and the optical distance that the reference light _S2 emitted from the second light source 120 travels within the prism unit 130 from when it enters the prism unit 130 until it enters the first photodetector 160 is 2h for reflected light _S21 ' and 2.5h for reflected light _S22 '.

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.

Therefore, in this laser rangefinder 100, as described above, the S-polarized measurement light S1 and reference light S2 are converted from divergent light to parallel light from the first and second light sources ₁₁₀ , 120 via the reflective (polarization-preserving) collimators 111, ₁₁₂ and are incident on the prism unit 130.Since the light path passes through air, which has little dispersion, group delay distribution is unlikely to occur in the beam cross section, and the light is incident on 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, and high-precision optical interference observation without ghosts can be performed.

In addition, this laser rangefinder 100 outputs the difference between the distance to the reference surface 155 and the distance to the measurement surface 150. Therefore, 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 measurement accuracy.

In addition, 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, the optical loss increases, but the quarter-wave (λ/4) plates 115, 116 are not necessary.

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 a non-modulated 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.

Even in this case, by using an interferometer equipped with an interferometer prism like the laser rangefinder 100 described above, 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.

In other words, while a displacement meter only measures changes in distance, by using an interferometer equipped with the above-mentioned interferometer prism, it is possible to define the distance as 0 when the measurement surface and reference surface are aligned. Therefore, even when correcting for variations in the refractive index of the atmosphere, an unknown distance (dead path) does not occur 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, as the reference light and measurement light are not emitted in the same direction.

As described above, by using the prism unit 130, into which the measurement light _S1 and reference light _S2 from the first and second light sources 110 and 120 are converted from divergent light to parallel light via the reflective (polarization-preserving) collimators 111 and 112 and incident, as an interference optical meter, measurement values such as displacement, distance, and distribution can be obtained by the signal processing unit 180 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 each interference light in the first and second photodetectors 160 and 170 are equal to each other, and even if the temperature of the prism unit 130 changes, the relative relationship between the respective interference lights detected in the first and second photodetectors is constant, making it possible to perform high-precision optical interference observation without ghosts.

The present invention can be used not only as the laser rangefinder 100 described above, but also as an interferometer for optical coherence tomography (OCT), for example. By using an interferometer equipped with the above-mentioned interferometer prism, it is possible to improve the accuracy of industrial applications of OCT.

When an interferometer equipped with the above-mentioned interferometer prism is used 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 single-shot 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.

Here, in the above-mentioned laser rangefinder 100, which calculates the distance to only one point, the interference signal detected by the second photodetector 170 serves to clarify the reference plane.

When an interferometer equipped with the above-mentioned interferometer prism is applied to OCT, one of the interference signals detected by the two photodetectors not only serves to clarify the reference plane, but also serves another purpose.

In other words, 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 a distribution of reflection points with respect to distance (point spread function), the width of the distribution can 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.

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.

Furthermore, this result can be used to perform calculations to correct the variance of the interference signal detected by the first photodetector 160 in real time.

This allows for clearer OCT images to be obtained.

Here, in the laser distance meter 100, the prism unit 130 is used as an interference optical meter, and measurement light S 1 and reference light S ₂ are emitted from the first and second light sources 110 and 120 via reflection type (polarization-preserving) collimators 111 and 112. In the present invention, the light emitted from _the light projecting unit is converted from divergent light to parallel light and incident on the prism unit 130. However, the present invention is not limited to the laser rangefinder 100. 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 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 returned, 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. In the present invention, a reflective optical system is provided in the light projecting unit that irradiates the measurement object with modulated light, and the reflective optical system is used to eliminate the distribution of group delay in the cross section of the measurement light beam, thereby eliminating measurement errors caused by the distribution of group delay in the cross section of the measurement light beam, and an optical rangefinder that measures and calculates the distance to the measurement object with high accuracy by a signal processing unit from the time delay of the measurement signal obtained by the light receiving unit can be realized.

That is, the optical distance meter according to the present invention includes a light projection unit consisting of 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 the light reflected by the measurement object from the measurement light irradiated to the measurement object via the light projection 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 that is reflected and returned by the measurement object and obtained 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 the measurement signal based on the relative relationship between the measurement signal and a reference signal that is a signal that generates the measurement light or reference light or a signal generated by the measurement light or reference light.

The reflective optical system provided in the light projection unit is a reflective collimator that converts modulated light emitted from the light output end into space 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.

The optical distance meter according to the present invention is an interference detection type optical distance meter 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. For example, as shown in FIG. 4, the optical distance meter 10 can be equipped with 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 to the measurement object 1 and superimposes the measurement light SS' reflected by the measurement object 1 and returned to obtain interference light, by superimposing the reference light SS' and the measurement light SS' as shown in FIG. 4.

In this optical range finder 10, 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 is incident on a beam splitter 13 as parallel modulated light S via a light projecting unit 12 consisting of a reflective (polarization-preserving) collimator, the parallel modulated light S is separated into a reference light SR and a measurement light SS by the beam splitter 13, the reference light SR is irradiated onto a reference surface 16 and the measurement light SS is irradiated onto a measurement object 1, and 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 are superimposed via the beam splitter 13 to obtain interference light, which is received by a light receiving unit 14, thereby detecting a measurement signal as an interference signal.

In this optical range finder 10, the beam splitter 13, which superimposes the reference light SR' reflected back by the reference surface 16 and returned and the measurement light SS' reflected back by the measurement object 1, separates the modulated light S emitted from the light source 11 via the light projector 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 measurement object 1 with the measurement light SS, which is the reference light SR' reflected back by the reference surface 16 and returned, i.e., the reference light SR' that has passed through a round-trip optical path including the reference surface 16 that reflects the reference light SR as the reference optical path, and the measurement light SS, which is reflected back by the measurement object 1 and returned, to obtain interference light.

In this optical distance meter 10, the light projecting unit 12 is a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 11 into a parallel measurement light SS. The light projecting unit 12 is a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space into a parallel measurement light SS. The light projecting unit 12 is a reflective (polarization-preserving) collimator that converts the modulated light S into a parallel measurement light SS. The light projecting unit 15 analyzes the interference signal obtained as the detection output of the interference light by the light receiving unit 14 based on the relative relationship between the measurement signal by the measurement light SS reflected back by the measurement object 1 and the 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. This makes 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 reflected back by the reference surface 16 and the measurement light SS reflected back by the measurement object 1.

In addition, 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.

In addition, in this optical rangefinder 10A, the components other than the reflective focuser 17 are the same as those in the optical rangefinder 10 described above, so the same reference numerals are used in the figure and detailed explanations are omitted.

The reflective collimator constituting the light-projecting unit 12 and the reflective focuser 17 provided in the light-receiving unit 14 are of the same optical system, with the incident and exit sides reversed.

In this optical distance meter 10A, the light projecting unit 12 is composed of a reflective (polarization-preserving) collimator that converts the modulated light S emitted into space from the light source 11 into a parallel measurement light SS, and the reflective focuser 17 is provided in the light receiving unit 14. The light receiving element of the light receiving unit 14 detects the interference light with high sensitivity without causing a group delay distribution in the beam cross section and without group velocity optical path difference. In the signal processing unit 15, the interference signal obtained as the detection output of the interference light by the light receiving unit 14 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 the measurement light or reference light or a signal generated by the measurement light or reference light. 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.

Also, an optical rangefinder using the interference detection method, such as the optical rangefinder 20 shown in FIG. 6, includes two light-projecting units 22S, 22R, each of which is made up of a reflection optical system into which modulated light S emitted from a light source 21 into space is branched and incident, and the interference optical system 23 irradiates the modulated light S emitted from one of the light-projecting units 22S as measurement light SS onto the measurement object 1, and superimposes the measurement light SS' reflected back by the measurement object 1 and the modulated light S emitted from the other light-projecting unit 22R as reference light SR on the measurement light SS' to obtain interference light.

In this optical rangefinder 20, the reflective optical system provided in the two light projecting units 22S and 22R is a reflective collimator that converts the modulated light S emitted into space from the light source 21 and branched into parallel light.

In the interference optical system 23 of this optical range finder 20, modulated light S containing multiple wavelengths emitted into space from the light source 21 is incident on the first beam splitter 23A as measurement light SS via the 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 the second beam splitter 23B as reference light SR via the 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 back by the object to be measured 1 is reflected by the first beam splitter 23A and enters the second beam splitter 23B, whereby the measurement light SS' reflected back 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 the detection output of the interference light by the light receiving unit 24.

Then, 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 due to the measurement light SS reflected and returned by the measurement object 1 and the reference signal which is a signal generating the measurement light or reference light or a signal generated by the measurement light or reference light, and is thereby able to calculate with high accuracy the distance to the measurement object 1 from the time difference (phase difference) between the reference light SR and the measurement light SS' reflected and returned by the measurement object 1.

In this optical rangefinder 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, it is necessary for the light to 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 wavelengths may be separated and detected using a wavelength dispersion element such as a diffraction grating, and the light receiving element is not limited to a single detection element.

In this optical distance meter 20, the first light projecting unit 22S is made of a reflective (polarization-preserving) collimator that converts the modulated light S emitted from the light source 21 into space into a parallel measurement light SS, and the second light projecting unit 22R is made of a reflective (polarization-preserving) collimator that converts the modulated light S emitted from the light source 21 into space into a parallel reference light SR. In this manner, the beam cross section is less likely to have a distribution of group delay and is not accompanied by a 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 by the measurement light SS' reflected and returned by the measurement object 1 and the signal that drives the light source 21, and the distance to the measurement object 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 measurement object 1.

In addition, in the optical rangefinder 20, as in the optical rangefinder 20A shown in FIG. 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.

In addition, in this optical rangefinder 20A, the components other than the reflective focuser 27 are the same as those in the optical rangefinder 20 described above, so the same reference numerals are used in the figure and detailed explanations are omitted.

The reflective collimator constituting the light-projecting unit 22 and the reflective focuser 27 provided in the light-receiving unit 24 use the same optical system with the incident and outgoing sides reversed.

In this optical distance meter 20A, the first light projecting unit 22S is made of a reflective (polarization-preserving) collimator that converts the modulated light S emitted from the light source 21 into space into a parallel measurement light SS, the second light projecting unit 22R is made of a reflective (polarization-preserving) collimator that converts the modulated light S emitted from the light source 21 into space into a parallel reference light SR, and the reflective focuser 27 provided in the light receiving unit 24 is unlikely to cause a group delay distribution in the beam cross section, and is not accompanied by a group velocity optical path difference, and is detected by the light receiving element of the light receiving unit 24. By detecting the interference light with high sensitivity, and analyzing the interference signal obtained as the detection output of the interference light by the light receiving unit 24 in the signal processing unit 25 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, the distance to the measurement object 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 measurement object 1.

In addition, an optical range finder using the interference detection method can also be configured, for example, as the optical range finder 30 shown in Figure 8.

This optical rangefinder 30 comprises two light sources 31S, 31R that radiate modulated light that is coherent with each other into space, and two light-projecting units 32S, 32R, each consisting of a reflection optical system, into which the modulated light _S1 , _S2 radiated into space from the two light sources 31S, 31R are incident. The interference optical system 33 irradiates the modulated light _S1 emitted from one of the light-projecting units 32S as measurement light SS onto the measurement object 1, 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.

That is, the optical distance meter 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 inputs modulated light _S1 including a plurality of wavelengths emitted from the first light source 31S into space via a first light projecting unit 32S made of a reflective (polarization-preserving) collimator to a first beam splitter 33A as measurement light S1, and inputs modulated light S1 including a plurality of wavelengths emitted from the second light source 31R into space via a first light projecting unit 32S made of a reflective (polarization-preserving) collimator to a first beam splitter 33A as measurement light _S1 . The reference light SR is incident on the second beam splitter 33B as the reference light SR via the second light-projecting unit 32R consisting of _a reflective (polarization-preserving) collimator, the measurement light SS passing through the first beam splitter 33A is irradiated onto the measurement object 1, and the measurement light SS' reflected and returned by the measurement object 1 is reflected by the first beam splitter 33A and incident on the second beam splitter 33B, whereby the measurement light SS' reflected and returned by the measurement object 1 and the reference light SR are superimposed on each other at the second beam splitter 33B by the interference optical system 33 to obtain interference light, and the interference light is received by the light-receiving unit 34 to obtain an interference signal obtained as a detection output of the interference light by the light-receiving unit 34.

In this optical distance meter 30, the first light-projecting unit 32S is composed 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 is composed 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 no group velocity optical path difference is involved. In the signal processing unit 35, an interference signal obtained as a detection output of the interference light by the light-receiving unit 34 is analyzed based on a relative relationship between a measurement signal by the measurement light SS reflected and returned by the measurement object 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 the distance to the measurement object 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 measurement object 1.

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 onto the light receiving unit 34, allowing the light receiving element of the light receiving unit 34 to detect the interference light with high sensitivity.

In addition, an optical range finder using the interference detection method can also be configured, for example, as optical range finder 40 shown in Figure 9.

This optical range finder 40 is equipped with 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.

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 unit 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 by 90 degrees to be incident on a second beam splitter 43B, while the other measurement light SS that has passed through the first beam splitter 43A is irradiated onto the object to be measured 1.

In addition, modulated light _S2 containing a plurality of wavelengths emitted into space from the second light source 41R is incident on the third beam splitter 43C as reference light SR via a second light-projecting unit 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 transmitted through the third beam splitter 43C is incident on the fourth beam splitter 43D, while the other reference light SR reflected by the third beam splitter 43C and bent by 90° is incident on the second beam splitter 43B.

The interference optical system 43 in the 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 receives this reference interference light with the reference light receiving unit 44R to obtain a reference interference signal as a detection output of the reference interference light by the reference light receiving unit 44R.

In addition, in the interference optical system 43 of the optical range finder 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' that is reflected back by the measurement object 1 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 the measurement interference light is received by the measurement light receiving unit 44S to obtain a measurement interference signal as a detection output of the measurement interference light by the measurement light receiving unit 44S.

In this optical range finder 40, the first light projecting unit 42S is made of a reflective (polarization-preserving) collimator that converts the modulated light S1 emitted into space from the first light source 41S into a parallel measurement light SS, and the second light projecting unit 42R is made of a reflective (polarization-preserving) collimator that converts the modulated light S2 emitted into space from the second light source 41R into a parallel reference light SR. In this way, the beam cross section is less likely to have a distribution of group delay and is not accompanied by a group velocity optical path difference. In the signal processing unit 45, the distance to the measurement object 1 can be calculated with high accuracy from the time difference (phase difference) between the reference interference signal obtained by the reference light detecting unit 44R and the measurement interference signal obtained by the measurement light receiving unit 44S.

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 using the light receiving element of the reference light detection unit 44R, and to detect the measurement interference light with high sensitivity using the light receiving element of the measurement light receiving unit 44S.

Here, in this optical range finder 40, the first beam splitter 43A to the fourth beam splitter 43D and the total reflection mirror 43E constitute the interference optical system 43, and this interference optical system 43 can be an interferometer prism having an integrated 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. The laser range finder 100 shown in FIG. 1 described above is a specific example of an interference detection type optical range finder that has an interferometer prism as the prism unit 130, 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.

In addition, reflective collimators that convert modulated light emitted from a light source into space into parallel light and reflective focusers that convert parallel light into convergent light can also be applied to laser light emitted into space via optical fibers.

That is, an optical range finder using the interference detection method can be configured, for example, as the optical range finder 50 shown in FIG. 10.

This optical distance meter 50 includes a light source unit 51 consisting of two optical comb light sources 51S and 51R that output a measurement light SS and a reference light SR that are periodically modulated in intensity or phase and have different modulation periods, an optical fiber interferometer 52 in which the measurement light SS is input from the first optical comb light source 51S of the light source unit 51 to a first optical coupler 53A via an optical fiber and the reference light SR is input from the second optical comb light source 51R to a second optical coupler 52B via an optical fiber, and a fourth optical coupler 53B in which the reference light SR is input from the second optical comb light source 51R to a second optical coupler 52B via an optical fiber. The optical fiber interferometer 53 is provided with a measurement light detector 54S connected to the fifth optical coupler 53D via two optical fibers, a reference light detector 54R connected to the fifth optical coupler 53E of the optical fiber interferometer 53 via two optical fibers, a reflective optical system 56 connected to the 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 the measurement signal obtained by the measurement light detector 54S and the reference signal obtained by the reference light detector 54R.

The optical fiber interferometer 53 provided in this optical range finder 50 is composed 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 the third optical coupler 53C and the fourth optical coupler 53D, respectively. 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 the fifth optical coupler 53D, respectively. Furthermore, the third optical coupler 53C is connected to the fifth optical coupler 53D via an optical fiber.

In the optical fiber interferometer 53, the measurement light SS incident on the first optical coupler 52A is emitted into space from a reflective optical system 56 connected to the third optical coupler 53C via an optical fiber, and irradiates the measurement object 1. The measurement light SS' reflected by the measurement object 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.

The fifth optical coupler 53E is connected via an optical fiber to the second optical coupler 52B to which the reference light SR is incident, so that 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 interference light for measurement.

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 reflection side of the optical coupler, and outputs the light by splitting it into two.

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.

By receiving this measurement interference light with the measurement light receiving unit 54S, a measurement interference signal can be obtained as the detection output of the measurement interference light by the measurement light receiving unit 54S.

The measurement light receiving unit 54S calculates the difference between the two detection signals, making it possible to emphasize the interference signal and suppress intensity noise, thereby increasing the signal-to-noise ratio (S/N) of the measurement interference signal.

The fourth optical coupler 53D is connected to the first optical coupler 52A, into which the measurement light SS is incident, and the second optical coupler 52B, into which the reference light SR is incident, via optical fibers, so that 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.

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 reflection side of the optical coupler, and outputs the light by splitting it into two.

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.

By receiving this reference interference light with the reference light receiving unit 54R, a reference interference signal can be obtained as the detection output of the reference interference light by the reference light receiving unit 54R.

The reference light receiving unit 54S calculates the difference between the two detection signals, making it possible to enhance the interference signal and suppress intensity noise, thereby increasing the signal-to-noise ratio (S/N) of the reference interference signal.

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 measurement object 1 into parallel light, a focuser that converts the measurement light SS' reflected by the measurement object 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.

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. 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 the detection output by the measurement light receiving unit 54S that receives the measurement interference light obtained by the optical fiber interferometer 53, and the reference interference signal obtained as the detection output by the reference light receiving unit 54R that receives the reference interference light.

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 Figure 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.

This optical three-dimensional shape measuring device 80 includes, for example, a laser rangefinder 100 as shown in Figure 1, an optical scanning device 81 that scans the object to be measured 1 with measuring light _SC1 emitted from the laser rangefinder 100, and a signal processing device 82 that measures absolute distances to multiple points on the object to be measured 1 based on the output of the laser rangefinder 100 to obtain a three-dimensional image.

The laser rangefinder 100 emits measurement light S _C1 into space and scans the object to be measured 1 with the measurement light S _C1 using the optical scanning device 81, thereby measuring the absolute distance to the object to be measured 1 based on the measurement light _C1 ' reflected by the object to be measured 1 and returning via the optical scanning device 81.

The optical scanning device 81 includes a reflective scanning optical system that scans the measurement object 1 with the measurement light SC ₁ emitted from the laser range finder 100 .

That is, in this optical three-dimensional shape measuring device 80, the measuring light S _C1 emitted from the laser rangefinder 100 is irradiated from the optical scanning device 81 toward the object to be measured 1, the reflected light S _C1 ' from the object to be measured 1 returns to the laser rangefinder 100, and the absolute distance to the object surface is measured by the laser rangefinder 100.

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 range finder 100, and measures the three-dimensional shape of the object in a non-contact manner by accumulating the beam irradiation position and the absolute distance to that position for multiple points.

In this optical three-dimensional shape measuring device 80, the optical scanning device 81 is equipped with a reflective scanning optical system that scans the object to be measured 1, so that a group delay distribution is unlikely to occur in the beam cross section of the measurement light S _C1 and the reflected light S _C1 ' in the reflective scanning optical system, and no group velocity optical path difference is involved, so that the absolute distance to the surface of the object to be measured 1 can be measured with high accuracy by the laser rangefinder 100, and the signal processing device 82 acquires absolute distance information to the surface of the object to be measured 1 measured by the laser rangefinder 100, and accumulates the beam irradiation position and the absolute distance to that location for multiple points, thereby measuring the three-dimensional shape of the object non-contact.

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-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 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 (13)

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;
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 the reference light, or a signal that is generated by the measurement light or the reference light, and measures absolute distances to a plurality of points on the measurement object to obtain a stereoscopic image ;
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. The optical rangefinder according to claim 1, characterized in that the light-projecting unit 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. 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 . 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. 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. 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. 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. 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. 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. 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. 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. 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 . An evaluation method for evaluating the group delay distribution of measurement light emitted from the light-projecting unit of an optical rangefinder, the evaluation method being 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 .