JP2015072136A - Optical measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high-accuracy observation of interference of light without a ghost.SOLUTION: An optical measurement device is configured in such a manner that: first and second polarizers 103, 104 are respectively disposed at one of an incident end side and an exit end side of first and second polarization maintaining collimators 111, 112; measurement light S1 emitted from a first light source 110 and output via a first polarization maintaining optical fiber 101, and reference light S2 emitted from a second light source 120 and output via a second polarization maintaining optical fiber 102 are introduced via the polarization maintaining collimators 111, 112 and the polarizers 103, 104 into a prism unit 130 constituting an interferometer; and reflected light from a measurement surface irradiated with the measurement light S1 and reflected light from a reference surface irradiated with the reference light S2 via the prism unit 103 are superposed by the prism unit 130 to obtain interference light; and an interference signal obtained by detecting the interference light through first and second photodetectors 160, 170 is supplied to a signal processing unit 180.

Description

  The present invention detects interference light between the reflected light of the reference light irradiated to the reference surface and the reflected light of the measurement light irradiated to the measurement surface from the measurement surface, and detects the distance to the reference surface and the The present invention relates to an optical measurement device using an interferometer, such as a distance meter for obtaining a difference in distance to a measurement surface.

  2. Description of the Related Art Conventionally, distance measurement based on an optical principle using laser light is known as an active distance measurement method capable of measuring a precise point distance. In a laser rangefinder that measures the distance to the target object using laser light, the object to be measured is based on the difference between the time when the laser light is emitted and the time when the laser light reflected by the measurement object is detected by the light receiving element. The distance to is calculated. In addition, for example, the driving current of the semiconductor laser is modulated with a triangular wave or the like, the reflected light from the object is received using a photodiode embedded in the semiconductor laser element, and sawtooth appearing in the photodiode output current The distance information is obtained from the main wave number of the wave.

  The present inventors have previously proposed a distance meter configured as shown in FIG. 7 as a distance meter capable of measuring a long distance with high accuracy and in a short time (see, for example, Patent Document 1). ).

In this distance meter, the reference light S ₁ emitted from the first light source 1 and the measurement light S ₂ emitted from the second light source ₂ and the polarization beam splitter (PBS) 11 are overlapped with the polarization directions being orthogonal to each other. Then, the beam is split into two by reflected light and transmitted light by a beam splitter (BS) 12.

Then, the reflected light branched into two by the beam splitter (BS) 12 is incident on the reference light detector 3 through the polarizer 13, and the interference light S between the reference light S ₁ and the measurement light S ₂ included in the reflected light. ₃ is detected by the reference light detector 3, the reference light S ₁ included in the transmitted light, and the measurement light S ₂ are separated by the polarization beam splitter (PBS) 14, and the reference light S ₁ is the reference light S _1. The surface 4 is irradiated and reflected, and the measurement light S ₂ is irradiated and reflected on the measurement surface 6, superimposed by the polarization beam splitter (PBS) 14, and polarized as reflected light by the beam splitter (BS) 12. is incident on the measuring light detector 6 via the child 15, the interference signal of the reference light S ₁ and the interference light S ₄ of the measuring light S ₂ contained in the reflected light obtained by detecting by said measuring light detector 6 and Based on the time difference between Thus, the signal processing unit 7 can obtain the difference between the distance to the reference surface and the distance to the measurement surface from the speed of light and the refractive index at the measurement wavelength.

  In addition, an interferometer using an optical comb is capable of distance measurement capable of high-precision absolute distance measurement even with weak light reflection.

In the optical system of the distance meter, because the reference light S ₁ and the measuring light S ₂ passes through the same path, in order to measure the distance between the measurement surface 6 as a reference surface 4, it can be removed the influence of changes in the middle of the path There are advantages. In particular, there is a great merit that the influence of a medium whose refractive index changes greatly at a temperature such as glass that cannot be used as long as it constitutes a polarizing beam splitter (PBS) or a beam splitter (BS) is eliminated.

However, in order polarization state of the polarization beam splitter (PBS) and the middle of the route is not complete, there is a reference light S ₁ is mix problems in measuring beam S ₂ toward the measuring surface 6. Alternatively, there is a problem that the measurement light S ₂ is mixed with the reference light S ₁ toward the reference surface 4. Therefore, the measurement light detector 6, the measuring light S ₂ is detected interference unnecessary light be (ghost) is not returned, the problem when weak reflected light from the measuring face 6 is increased. This was one of the causes of measurement error.

Stray light in the range finder, the reference light S ₁ and the path of the measuring light S ₂ is generated due to incomplete, by reference light S ₁ and the measuring light S ₂ passes through the same path, that The merit of eliminating the influence of a medium such as glass whose refractive index of the path greatly changes is great. However, even in different paths, if the reference light S ₁ and the measuring light S ₂ is the same distance propagates the same medium at the same temperature, it is possible to reduce the influence of the medium.

  There can be many methods for constructing such an optical system, but it is limited to constructing an optical system that has a small adjustment mechanism, is small, and can be made planar.

  An interferometer using an optical comb can perform distance measurement capable of high-precision absolute distance measurement even with weak light reflection.

  However, the conventional interferometer has a problem that a ghost due to imperfection of the polarizing element occurs.

  Therefore, the inventors of the present invention have previously proposed a distance meter configured as shown in FIG. 8 as an optical measuring device capable of performing high-precision optical interference observation without ghost (for example, Patent Documents). 2).

The laser distance meter 200 includes a first light source 210 that emits measurement light S1, a second light source 220 that emits reference light S2, a measurement light S1 emitted from the first light source 210, and a second light source. The reference light S2 emitted from the light source 220 is incident through the polarization preserving collimators 211 and 212, and the measurement light S1 emitted from the first light source 210 is transmitted through the prism unit 230. The measurement surface 250 and the reference surface 255 to be irradiated, the measurement light S ₁ emitted from the first light source 210 and the reference light S ₂ emitted from the second light source 220 are superimposed via the prism unit 230. The first light detector 260 that detects the interference light between the measurement light S ₁ and the reference light S _2, and the measurement surface 2 of the measurement light irradiated on the measurement surface 250. The reflected light from the reference surface 255 and the reflected light from the reference surface 255 irradiated on the reference surface 255 are superimposed and incident via the prism unit 230, and the reflected light from the measurement light and the reflected light from the reference light are input. 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. A signal processing unit 280 that obtains a difference between the distance from the refractive index at the light speed and the measurement wavelength to the reference surface 255 and the distance to the measurement surface 250.

JP 2010-14549 A JP 2012-13574 A

  However, in the laser interferometer optical interferometer disclosed in Patent Document 2 previously proposed by the present inventors, a ghost that is generated due to the reference light and the measurement light passing through the same path. The problem was solved. However, when the optical interferometer and the light source are connected with a polarization maintaining light (PM) fiber, there is a ghost problem caused by the polarization maintaining optical fiber.

  There are two polarization modes in the polarization maintaining optical fiber, and the optical interferometer is used in either polarization mode. However, if light is mixed into the other polarization mode, the speed of light in the polarization mode is different, so that there is a problem that signals having different time differences overlap with interference signals. This ghost has greatly hindered the denial meter measurement, and has a large effect especially when the optical fiber is long.

  The laser interferometer optical interferometer disclosed in Patent Document 2 is composed of a plurality of optical elements. Each optical element is installed with its position and angle adjusted. In particular, the relative angle between the two collimators and the reference surface requires an accuracy of about several tens of seconds. Therefore, in assembling the optical system, a tool for precisely positioning and a tool for precise fixing are required. In addition, the assembly of the entire optical system is complicated due to the large number of parts.

  In addition, the optical element is installed in the housing, but in order to maintain the relationship of the relative angle of the optical element, the housing is made of, for example, Kovar having a thermal expansion coefficient close to that of the optical element, stainless steel having excellent strength, ceramics, etc. Produced with materials. Such a casing is made large and heavy because it is made so as to be mechanically stable.

  However, in order to construct a system in which the interferometer is attached to a robot or the like and the observation point is arbitrarily changed, a small and lightweight housing is required.

  Therefore, the present invention solves the above-described conventional problems, and solves the ghost problem caused by the polarization-maintaining optical fiber and can perform high-precision optical interference observation without ghost. The purpose is to provide.

  In addition, the present invention provides an optical measurement device that can perform high-precision optical interference observation without ghosting, is resistant to fluctuations in acceleration and environmental temperature, is small and lightweight, and is easy to assemble. Objective.

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

  In the present invention, the optical interferometer of the laser distance meter disclosed in Patent Document 2 previously proposed by the present inventors is improved, and the optical path of the light emitted from the light source via the polarization maintaining optical fiber By inserting a polarizer inside, the problem of ghost caused by the polarization maintaining optical fiber is solved.

  That is, the present invention is an optical measurement device, in which intensity or phase is modulated periodically, and first and second light sources that emit coherent measurement light and reference light having different modulation periods from each other, The first and second polarization preserving collimators in which the measurement light emitted from the first light source and the reference light emitted from the second light source are incident through the polarization preserving optical fiber, and The first and second polarizers provided on one of the incident end side and the emission end side of the first and second polarization preserving collimators, the measurement light and the reference light are converted into the first and second polarizations, respectively. A prism unit incident via a wave-preserving collimator, first and second polarizers, a measurement surface irradiated with measurement light emitted from the first light source via the prism unit, and the second The reference light emitted from the light source is the prism The reference surface irradiated through the knit, the measurement light emitted from the first light source, and the reference light emitted from the second light source are superimposed and incident via the prism unit, and the measurement light A first detector for detecting interference light between the reference surface and the reference light; a reflected light of the measurement light irradiated on the measurement surface by the measurement surface; and a reflection of the reference light irradiated on the reference surface by the reference surface Light is superimposed and incident via the prism unit, and a second photodetector that detects interference light between the reflected light of the measurement light and the reflected light of the reference light, and the first photodetector Signal processing for obtaining the difference between the distance from the refractive index at the speed of light and measurement wavelength to the reference plane and the distance to the measurement plane from the time difference between the detected interference signal and the interference signal detected by the second photodetector. Special features To.

  In the optical measurement apparatus according to the present invention, the prism unit includes a total reflection surface that forms an angle of 45 ° with respect to the optical path and two parallel surfaces on which the beam splitter film is formed and are perpendicular to the optical path and parallel to each other. Alternatively, a first rectangular prism having two surfaces that form a right angle and a surface on which the beam splitter film of the first rectangular prism is formed, and a slope is bonded to the surface with the beam splitter film interposed therebetween. One right-angle prism, a second splitter prism having a beam splitter film formed on one inclined surface, and the inclined surfaces bonded to each other with the beam splitter film interposed therebetween, and a third rectangular prism, which form an angle of 45 ° with respect to the optical path A second quadrangular prism pre-form having two surfaces parallel to each other on which a reflecting surface and a beam splitter film are formed, and two surfaces perpendicular to the optical path and parallel to or perpendicular to each other. And a fourth right-angle prism in which a slope is bonded to the surface on which the beam splitter film of the first square prism is formed with the beam splitter film interposed therebetween, and the first square prism One surface of the two surfaces perpendicular to the optical path and one surface of the two surfaces perpendicular to the first right-angle prism are arranged so that the beam splitter films are parallel to each other. One surface of two surfaces forming a right angle of one right-angle prism and one surface of the two surfaces forming a right angle with respect to the optical path of the second quadrangular prism and the fourth right-angle prism One surface of the two surfaces forming a right angle is bonded to one surface of the two surfaces forming the right angle of the second right angle prism so that the beam splitter films are perpendicular to each other. Measuring light The measurement light emitted from the first light source is converted into the first light by the prism unit through which the reference light is incident through the first and second polarization preserving collimators and the first and second polarizers. The beam is split into two by the beam splitter film formed on the quadrangular prism, and is emitted through the beam splitter film sandwiched between the inclined surfaces of the second right angle prism and the third right angle prism. And the reference light emitted from the second light source is split into two by the beam splitter film formed on the second quadrangular prism, and the measurement surface and the reference surface Each of the reflected light and the first photodetector and the second photodetector are output in a superimposed manner on a beam splitter film sandwiched between the slopes of the second right-angle prism and the third right-angle prism. In It can be obtained by forming an optical path to Isa.

  Further, in the optical measurement device according to the present invention, the first and second polarization maintaining collimators are provided with the first and second polarizers on one of the incident end side and the emission end side. A two-parallel beam collimator integrated with the casing is mounted on the casing, and a retroreflector is mounted on the casing as the reference plane together with the prism unit and the first and second photodetectors. Can be.

  In the present invention, the ghost problem caused by the polarization maintaining optical fiber is eliminated by inserting a polarizer in the optical path of the light emitted from the light source through the polarization maintaining optical fiber. It is possible to provide an optical measurement device that can perform accurate optical interference observation.

  Further, according to the present invention, the difference in optical distance experienced in the prism unit before the measurement light and the reference light are detected as the interference lights in the first and second photodetectors is equal to each other, and the prism unit Even if the temperature changes, the relative relationship between the interference lights detected by the first and second photodetectors is constant, and high-precision optical interference observation without ghosting can be performed.

  Further, according to the present invention, the first and second polarization preserving collimators are integrally formed with a casing in which the first and second polarizers are disposed on one of the incident end side and the emission end side. High-precision light without ghosting by adopting a structure in which the prism unit, the first and second photodetectors, and the retro-reflector are mounted as the reference plane on the housing mounted as the two parallel beam collimator It is possible to provide an optical measurement apparatus that can perform interference observation, is resistant to fluctuations in acceleration and environmental temperature, is small and lightweight, and is easy to assemble.

It is a block diagram which shows the structural example of the laser rangefinder to which this invention is applied. It is a figure which shows the ghost of the interference signal by a polarization maintaining optical fiber, (A) shows the case where a polarizer is inserted, (B) shows the case where a polarizer is not used. It is a top view which shows typically the structural example of the prism unit with which the said laser distance meter is equipped. It is a perspective view which shows the principal part of the other structural example of the laser distance meter to which this invention is applied. It is a figure which shows the structure of the 2 parallel beam collimator with which the laser rangefinder of the said other structural example is equipped, (A) is a perspective view, (B) is a principal part cross-sectional perspective view. It is a graph which shows the result of having calculated the deterioration of the signal with respect to the parallelism of the reflected light which injects into a photodetector supposing the case of wavelength 1550nm and beam diameter 3.5mm. It is a block diagram which shows the structure of the distance meter which the present inventors etc. have proposed previously. It is a block diagram which shows the other structure of the distance meter which the present inventors etc. have proposed previously.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.

  The present invention is applied to, for example, a laser distance meter 100 configured as shown in FIG.

The laser rangefinder 100 includes a first light source 110 that emits measurement light S ₁ , a second light source 120 that emits reference light S _2, and measurement light S ₁ emitted from the first light source 110. The prism unit 130 on which the reference light S ₂ emitted from the second light source 120 is incident, and the measurement surface on which the measurement light S ₁ emitted from the first light source 110 is irradiated via the prism unit 130. 150, the second reference light S ₂ emitted from the light source 120 is a reference surface 155 to be irradiated through the prism unit 130, the above has been measuring light S ₁ emitted from the first light source 110 a The first light detector 16 that detects the interference light between the measurement light S ₁ and the reference light S ₂ by superimposing and entering the reference light S ₂ emitted from the second light source 120 via the prism unit 130. 0, the reflected light of the measurement light irradiated on the measurement surface 150 by the measurement surface 150 and the reflected light of the reference light irradiated on the reference surface 155 by the reference surface 155 are superimposed via the prism unit 130. The second photodetector 170 detects the interference light between the reflected light of the measurement light and the reflected light of the reference light, the interference signal detected by the first photodetector 160, and the first And a signal processing unit 180 for obtaining a difference between the distance from the refractive index at the measurement speed and the speed of light to the reference surface 155 and the distance to the measurement surface 150 from the time difference between the interference signals detected by the two photodetectors 170. .

The first and second light sources 110 and 120 emit coherent measurement light S ₁ and reference light S ₂ that are periodically modulated in intensity or phase and have different modulation periods, respectively. Two light sources each having an optical modulator for emitting the measurement light S ₁ and the reference light S ₂ having the coherence, each of which is periodically modulated in intensity or phase and having different modulation periods, and the optical frequency comb mode interval is It consists of two different optical frequency comb generators or two pulsed light sources with different optical pulse repetition frequencies.

The first light source 110 emits S-polarized measurement light S ₁ through the polarization maintaining fiber 101 and the polarization maintaining collimator 111. The second light source 120 emits S-polarized reference light S ₂ through the polarization maintaining fiber 102 and the polarization maintaining collimator 112. The S-polarized measurement light S ₁ and the reference light S ₂ are incident on the prism unit 130 via polarizers 103 and 104 and half-wave (λ / 2) plates 113 and 114.

  The polarizers 103 and 104 are installed in alignment with one of the two polarization modes of the polarization maintaining fibers 101 and 102, respectively. Thereby, the unused component in the polarization mode of the polarization maintaining fibers 101 and 102 can be removed.

  For the polarizers 101 and 102, a polarizer using a crystal such as calcite, BBO, or rutile, a dielectric multilayer polarizer, a wire grid polarizer, a beam displacer, or a polar core that is a glass polarizer manufactured by Corning ( (Registered trademark), Cupo (registered trademark) manufactured by HOYA Co., Ltd., and the like can be used. Alternatively, a polarizing fiber that can guide only specific polarized light may be used.

  Here, an example of the ghost of the interference signal by the polarization maintaining fiber is shown in FIGS.

  (A) and (B) in FIG. 2 are observed by forcibly degrading the extinction ratio of the two polarization modes of the polarization-maintaining optical fiber, and in particular, creating a state in which a ghost is easily generated. The case where a polarizer is inserted is shown, and (B) shows the case where a polarizer is not used.

  In FIG. 2B, a signal that is not in FIG. 2A is superimposed and a ghost is observed, but by inserting a polarizer, as shown in FIG. A ghost can be hardly recognized.

  Therefore, by inserting a polarizer either on the incident end side or on the exit end side of the polarization maintaining collimator, the ghost problem caused by the polarization-maintaining optical fiber can be solved, and high-precision optical interference observation without ghosting can be achieved. It can be performed.

  In the laser distance meter 100, the prism unit 130 includes, as shown in FIG. 3, 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 The trapezoidal prism 135 and the fourth right-angle prism 136 are bonded together to form an interferometer prism.

  As shown in FIG. 3, the prism unit 130 includes two surfaces 131a and 131b that are perpendicular to the optical path and perpendicular to each other, a total reflection surface 141A that forms 45 ° with respect to the optical path, and a beam splitter film 142A. The first trapezoidal prism 131 having two surfaces 131c and 131d parallel to each other, and the surface 131d of the first trapezoidal prism 131 on which the beam splitter film 142A is formed, sandwiching the beam splitter film 142A. A first right-angle prism 132 to which the inclined surface 132c is bonded and a polarizing beam splitter film 143 formed on one of the inclined surfaces, and a second right-angle prism 133 to which the inclined surfaces 133c and 134c are bonded with the polarizing beam splitter film 143 interposed therebetween. And the third right-angle prism 134 and perpendicular to the optical path. A second trapezoidal prism 135 having two surfaces 135c and 135d in which a total reflection surface 141B and a beam splitter film 142B are formed at 45 ° with respect to the two surfaces 135a and 135b and parallel to each other; And a fourth right-angle prism 136 having a slope 136c bonded to the surface 135d of the second trapezoidal prism 135 on which the beam splitter film 142B is formed, with the beam splitter film 142B interposed therebetween.

  The prism unit 130 includes one surface of two surfaces 131a and 131b perpendicular to the optical path of the first trapezoidal prism 131 and two surfaces 132a perpendicular to the first right prism 132. One surface of 132b is bonded to one surface of the two surfaces forming the right angle of the first right-angle prism 132 so that the beam splitter film 142A and the polarization beam splitter film 143 are perpendicular to each other. One surface of the two surfaces 132a and 132b perpendicular to the optical path of the second trapezoidal prism 135 and one surface of the two surfaces 136a and 136b perpendicular to the fourth rectangular prism 136 are The second right-angle prism 136 is arranged so that the beam splitter film 142B and the polarization beam splitter film 143 are parallel to each other. It is bonded to one surface of two surfaces at right angles.

  The prism unit 130 includes 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 trapezoid prism 135, and the fourth right-angle prism 136. The trapezoidal prism is configured by integrating them together, and antireflection (AR) 144 and 145 films are deposited on the upper surface and the bottom surface of the trapezoidal prism.

Then, in the laser rangefinder 100, the first light source 110 emits the measuring beam _{S 1} of S-polarized light through the polarization maintaining collimator 111, also the second light source 120, polarization maintaining collimator An S-polarized reference light S ₂ is emitted through the line 112. The measurement light S ₁ and the reference light S ₂ are incident on the prism unit 130 via half-wave (λ / 2) plates 113 and 114.

The measurement light S ₁ and the reference light S ₂ incident on the prism unit 130 pass through the polarization beam splitter film 143 through one surface 133 a of the two surfaces 133 a and 133 b forming the right angle of the second right-angle prism 133. And is split into two measuring beams S _1S and S _1P and reference beams S _2S and S _2P by the polarizing beam splitter film 143, respectively.

The measurement light _S1S of one polarized light reflected by the polarizing beam splitter film 143 is reflected by the surface 131c of the first trapezoidal prism 131 on which the total reflection surface 141A is formed and is bent by 90 ° to be beam splitter. is incident on the film 142A, this by the beam splitter film 142A measuring beam _{S 1S} of said one polarization is 1: two measuring beam _S 11 1 _ratio, is divided into _{S 12.}

The measurement light S ₁₁ , S ₁₂ branched into two at a ratio of 1: 1 by the beam splitter film 142 A is a surface in which one measurement light S ₁₁ is perpendicular to the optical path of the first right-angle prism 132. is emitted via 132a, also other measurement light S ₁₂ is bent 90 ° is reflected by a surface 131c formed in the total reflection surface 141A of the perpendicular to the optical path of the first trapezoidal prism 131 The light is emitted through the surface 131a formed.

Further, the measurement light S _1P of the other polarized light that has passed through the polarizing beam splitter film 143 is emitted from a surface 133a that is perpendicular to the optical path of the second right-angle prism 133, and has a quarter wavelength (λ / 4). ) The circularly polarized measurement light S _1C is made to irradiate the measurement surface 150 through the plate 115.

The reflected light S _1C ′ reflected perpendicularly 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 polarized beam. The reflected light S _1S ′ of one polarized light reflected by the splitter film 143 is reflected by the surface 135c of the second trapezoidal prism 135 on which the total reflection surface 141B is formed and is bent by 90 ° to the beam splitter film 142B. is incident, the beam splitter film 142B by the reflected light _{S 1S} of said one polarization 'is 1: two reflected light _{S 11} 1 ratio' _is split into _{S 12} '.

The reflected light S ₁₁ ′ and S ₁₂ ′ branched into two at a ratio of 1: 1 by the beam splitter film 142 B has one reflected light S ₁₁ ′ perpendicular to the optical path of the fourth right-angle prism 136. The other reflected light S ₁₂ ′ is reflected by the surface 136c on which the total reflection surface 141B is formed and bent by 90 °. Then, the light is emitted through a surface 135 a perpendicular to the optical path of the second trapezoidal prism 135 and is incident on the second photodetector 170.

One polarized reference light S _2S reflected by the polarizing beam splitter film 143 is incident on the beam splitter film 142 A, and the one polarized reference light S _2S is in a ratio of 1: 1 by the beam splitter film 142 A. Is branched into two reference lights S ₂₁ and S ₂₂ .

The reference light S ₂₁ , S ₂₂ branched into two at a ratio of 1: 1 by the beam splitter film 142 A is a surface in which one reference light S ₂₁ is perpendicular to the optical path of the first right-angle prism 132. is output through the 132a are incident on the first photodetector 160, also the first other reference light S ₂₂ is bent has been reflected 90 ° by the formed surface 131c of the total reflection surface 141A The light is emitted through a surface 131 a perpendicular to the optical path of one trapezoidal prism 131 and is incident on the first photodetector 160.

The reference light S _2P of the other polarization that has passed through the polarizing beam splitter film 143 is emitted from a surface 133a that is perpendicular to the optical path of the second right-angle prism 133, and is ¼ wavelength (λ / 4). ) The circularly polarized measurement light S _2C is passed through the plate 116 and irradiated onto the reference surface 155.

The reflected light S _2C ′ reflected perpendicularly 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 polarized beam. The reflected light S _2S ′ of one polarized light reflected by the splitter film 143 is reflected by the surface 135c of the second trapezoidal prism 135 where the total reflection surface 141B is formed, and is bent by 90 ° to the beam splitter film 142B. is incident, the beam splitter film 142B by the reflected light _{S 2S} of said one polarization 'is 1: two reflected light _{S 21} 1 ratio' _is split into _{S 22} '.

The reflected light S ₂₁ ′ and S ₂₂ ′ branched into two at a ratio of 1: 1 by the beam splitter film 142 B has one reflected light S ₂₁ ′ perpendicular to the optical path of the fourth right-angle prism 136. is incident on the second photodetector 170 is emitted through the surface 136a forming the also bent 90 ° is reflected by the surface 136c of the other of the reflected light S _{22 'is} formed of the total reflection surface 141B Then, the light is emitted through a surface 135 a perpendicular to the optical path of the second trapezoidal prism 135 and is incident on the second photodetector 170.

The first photodetector 160 detects interference light between the measurement light S ₁ and the reference light S _2, and is a beam formed on the first trapezoidal prism 131 of the prism unit 130. The interference light beams of the measurement light beams S ₁₁ and S ₁₂ and the reference light beams S ₂₁ and S ₂₂ that are superimposed on the splitter film 142A and branched into two are detected by the two photodetectors 161A and 161B, and the difference between them is differentially detected. Detection is performed by the detector 162.

The second photodetector 170 detects the interference light of the reflected light S _1C ′ from the measurement surface 150 and the reflected light S _2C ′ from the reference surface 155, and includes the prism unit 130. Interference between the reflected light beams S ₁₁ ′ and S ₁₂ ′ and the reflected light beams S ₂₁ ′ and S ₂₂ ′ that are superposed on the beam splitter film 142B formed on the second trapezoidal prism 135 and branched into two. The light is detected by the two photodetectors 171A and 171B, and the difference is detected by the differential detector 172.

The signal processing unit 180, a time difference of the interference signal obtained by detecting interference light of the measurement light S ₁ and the reference light S ₂ by the first optical detector 160, the second optical detector Based on the time difference between the interference signals obtained by detecting the interference light of the reflected light S _1C ′ from the measurement surface 150 and the reflected light S _2C ′ from the reference surface 155 by 170, the light velocity and the refractive index at the measurement wavelength are calculated. Processing for obtaining an absolute value of a distance difference between the distance to the reference surface 155 and the distance to the measurement surface 150 is performed.

In the laser rangefinder 100, and the height of the prism unit 130 i.e. the trapezoidal prisms is h, the measurement light S ₁ emitted from the first light source 110 is incident on the prism unit 130, the first light optical distance propagating in the prism unit 130 before being incident on the detector 160, measurement light _{S 11} is 2h, the measuring light _{S 12} is 2.5 h, which is emitted from the first light source 110 The optical distance that the light S ₁ enters the prism unit 130 and propagates through the prism unit 130 before entering the second photodetector 170 is 3h for the reflected light S ₁₁ ′ and the reflected light S _12. 'Is 3.5h.

On the other hand, the reference light S ₂ emitted from the second light source 120 enters the prism unit 130 and propagates through the prism unit 130 before entering the first photodetector 160. the distance is a reference light _{S 21} is 1.5 h, the reference light _{S 22} is 2h, the reference light _{S 2} emitted from the second light source 110 is incident on the prism unit 130, the second light detection The optical distance propagating through the prism unit 130 before entering the device 170 is 2 h for the reflected light S ₂₁ ′ and 2.5 h for the reflected light S ₂₂ ′.

That is, in the laser distance meter 100, the optical distance experienced by the measurement light S1 and the reference light S2 in the prism unit 130 before the interference light is detected by the _first and _second photodetectors 160 and 170. Are equal to each other at 1 h.

  Therefore, in the laser distance meter 100, 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 and 170 is constant, and ghost Highly accurate optical interference observation can be performed.

  The laser distance meter 100 outputs the absolute value of the distance difference between the distance to the reference surface 155 and the distance to the measurement surface 150. Therefore, by installing the measurement surface 150 and the reference surface 155 close to each other, The measurement accuracy can be increased by further reducing the influence of the refractive index change in the atmosphere.

  In the laser distance meter 100, the polarizing beam splitter film 143 sandwiched between the inclined surfaces 133c and 134c of the second right-angle prism 133 and the third right-angle prism 134 can be replaced with a beam splitter film. In this case, although the optical loss increases, the quarter wavelength (λ / 4) plates 115 and 116 become unnecessary.

Here, in the laser rangefinder 100 and the polarizer 103, 104 provided on the exit end side of the polarization maintaining collimator 111,104, the S-polarized light of the measuring beam _{S 1} and the reference light _{S 2} is the polarizer 103, 104 and the half wavelength (λ / 2) plates 113 and 114 are incident on the prism unit 130. Like the laser distance meter 100A shown in FIG. The polarization maintaining collimators 111 and 112 may be provided on the incident end side.

  The laser distance meter 100A includes polarization-maintaining collimators 111 and 112, ½ wavelength (λ / 2) plates, 113 and 114, ¼ wavelength (λ / 4) plates 115 and 116, a prism unit 130, and a reference surface. 155A, photodetectors 161A, 161B, 171A, 171B, and the like are formed of an interferometer mounted on a substrate 195.

  In the laser distance meter 100A, the same components as those of the laser distance meter 100 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the laser distance meter 100A, polarization maintaining collimators 111 and 112 are mounted on the substrate 195 as a two parallel beam collimator 190 in which a casing 191 is integrated.

  In other words, the two parallel beam collimator 190 is mounted on a case 191 in which two polarization preserving collimators 111 and 112 are integrated, as shown in (A) perspective view and (B) cross-sectional perspective view of FIG. An orientation / focus adjustment unit 192 and an XY positioning unit 193 at the positions of the polarization maintaining fibers 101 and 102 connected to the two polarization maintaining collimators 111 and 112 are provided.

  In the two parallel beam collimator 190, the two collimated lights emitted from the two polarization preserving collimators 111 and 112 are transmitted to each other by the tilt / focus adjustment unit 192 and the XY positioning unit 193 with reference to the same mirror. It can be adjusted and fixed in parallel, and the parallelism of the two collimated lights can be easily set to a level of several seconds.

  The two parallel beam collimator 190 includes polarizers 103 and 104, and the polarizers 103 and 104 are disposed on the incident side of the two polarization preserving collimators 111 and 112, respectively. The two-parallel beam collimator 190 includes the polarizers 103 and 104, thereby eliminating the ghost problem caused by the polarization-maintaining fibers 101 and 102 to be connected and enabling high-precision optical interference observation without the ghost. A simple laser distance meter 100A can be constructed.

  Further, the two-parallel beam collimator 190 having such a structure requires a precision positioning tool and a precision fixing tool at the time of assembly. However, the technique used for positioning and fixing is a normal collimator. This is a production technology that simplifies the assembly process. In addition, since the two parallel beam collimator 190 has a monocoque structure, it is mechanically strong, and even if it is made of a robust material, it is smaller than the entire interferometer and does not affect the overall weight. .

  In the laser distance meter 100A, a retro reflector such as a corner retro reflector is mounted on the substrate 195 as the reference surface 155A.

  In the interferometer including the reference plane 155A using the two parallel beam collimator 190, the prism unit 130, and the retro-reflector, the installation position and the installation angle of each component have a mechanical installation accuracy, for example, an accuracy of 0.2 mm and an angular accuracy of 0. Even if it is about 3 degrees, the accuracy of each part satisfies the condition that the interference signal is automatically obtained, so that the parallelism of the beam in the interferometer is kept at about several tens of seconds, and the interference signal is Obtained automatically. Although it is necessary to align the photodetectors 161A, 161B, 171A, and 171B, the alignment can be easily performed by selecting a detection surface having a diameter of about 100 μm. Therefore, in this laser distance meter 100A, it is not necessary to adjust and fix a plurality of optical elements with high accuracy, and the man-hour for the entire assembly is simplified.

  Further, in this laser distance meter 100A, even if the housing of the interferometer is made small and light, an interference signal is not lost due to fluctuations in acceleration and environmental temperature, and the optical distance measuring device is highly reliable. .

  Next, conditions for automatically obtaining an interference signal will be described.

For example, the intensity of the interference signal detected by the photodetector 171A is determined by the parallelism E between the reflected light S ₁₁ ′ and the reflected light S ₂₁ ′ incident on the photodetector 171A.

Here, when the target is an ideal vertical reflection, the maximum value of the parallelism of the reflected light S ₁₁ ′ and the reflected light S ₂₁ ′ determined by the accuracy of the interferometer is Emax, and the two parallel beam collimators 190. The parallelism of the two beams is A, the beam deflection accuracy of the half-wavelength (λ / 2) plates 113 and 114 is B, the beam deflection accuracy of the retroreflector used as the reference surface 155A is C, and the prism unit. When the parallelism of the two surfaces 135c and 135d of the second trapezoidal prism 135 constituting 130 is D,
Emax = A + 2 * B + C + 2 * n * D
It becomes. Here, n is the refractive index of the material of the prism unit 130.

  FIG. 6 shows a graph in which signal deterioration with respect to the parallelism E is calculated on the assumption that the wavelength is 1550 nm and the beam diameter is 3.5 mm. In this case, for example, the condition for obtaining an interference center with a loss of 3 dB or less may be that the maximum value Emax of the parallelism is about 50 seconds or less.

100,100A laser distance meter,
101, 102 Polarization-maintaining optical fiber 103, 104 Polarizer 110 First light source,
111, 112 polarization preserving collimator,
113, 114 1/2 wavelength (λ / 2) plate,
115, 116 1/4 wavelength (λ / 4) plate,
120 second light source,
130 prism unit,
131 first trapezoidal prism,
131A first parallelogram prism;
132 a first right angle prism;
133 second right angle prism,
134 a third right angle prism,
135 second trapezoidal prism,
135A second parallelogram prism,
136, 236 the fourth right angle prism,
141A, 141B Total reflection surface,
142A, 142B beam splitter film,
143, polarizing beam splitter film,
144, 145, antireflection (AR) film,
150 measuring surface,
155 reference plane,
155A Reference surface (retro reflector),
160 a first photodetector;
161A, 161B, 171A, 171B photodetector,
162,172 differential detector,
170 second photodetector,
180 Signal processor 190 Two parallel beam collimator 191 Case 195 Substrate

Claims (3)

First and second light sources that emit coherent measurement light and reference light, the intensity or phase of which are periodically modulated and the modulation periods of which are different from each other;
First and second polarization preserving collimators into which the measurement light emitted from the first light source and the reference light emitted from the second light source are respectively incident via a polarization preserving optical fiber;
First and second polarizers provided on one of the incident end side or the emission end side of the first and second polarization preserving collimators;
A prism unit on which the measurement light and the reference light are incident via the first and second polarization maintaining collimators and the first and second polarizers;
A measurement surface on which measurement light emitted from the first light source is irradiated via the prism unit;
A reference surface on which the reference light emitted from the second light source is irradiated through the prism unit;
The measurement light emitted from the first light source and the reference light emitted from the second light source are superimposed and incident via the prism unit, and the interference light between the measurement light and the reference light is detected. 1 photodetector;
Reflected light of the measurement light irradiated on the measurement surface by the measurement surface and reflected light of the reference light irradiated on the reference surface by the reference surface are superimposed and incident via the prism unit. A second photodetector for detecting interference light between the reflected light and the reflected light of the reference light;
From the time difference between the interference signal detected by the first photodetector and the interference signal detected by the second photodetector, the distance from the refractive index at the speed of light and measurement wavelength to the reference surface and the measurement surface An optical measurement device comprising: a signal processing unit for obtaining a difference in distance between the two. The prism unit has a total reflection surface forming 45 ° with respect to the optical path, two surfaces formed with a beam splitter film and parallel to each other, and two surfaces perpendicular to the optical path and parallel to or perpendicular to each other. A first rectangular prism, a first rectangular prism in which the beam splitter film of the first square prism is formed and a slope is bonded with the beam splitter film interposed therebetween; The beam splitter film is formed, the second right angle prism and the third right angle prism having the slopes bonded to each other with the beam splitter film interposed therebetween, the total reflection surface forming 45 ° with respect to the optical path, and the beam splitter film are formed. A second quadrangular prism having two parallel surfaces and two surfaces that are perpendicular to the optical path and parallel or perpendicular to each other; and a top of the first quadrangular prism. A surface on which the beam splitter film is formed and a fourth right-angle prism having slopes bonded to each other with the beam splitter film interposed therebetween, and two surfaces perpendicular to the optical path of the first quadrangular prism One surface of the first right-angle prism and one surface of the two surfaces forming the right angle of the first right-angle prism are two surfaces that form a right angle of the first right-angle prism so that the beam splitter films are parallel to each other. One surface of two surfaces that are bonded to one surface of the second rectangular prism and are perpendicular to the optical path of the second quadrangular prism and one surface of the two surfaces that are perpendicular to the fourth rectangular prism Is bonded to one of the two surfaces forming the right angle of the second right angle prism so that the beam splitter films are perpendicular to each other,
Measurement light emitted from the first light source by the prism unit through which the measurement light and the reference light are incident through the first and second polarization maintaining collimators and the first and second polarizers The beam is split into two by the beam splitter film formed on the first quadrangular prism and is emitted through the beam splitter film sandwiched between the inclined surfaces of the second right prism and the third right prism. The measurement surface and the reference surface are irradiated, and the reference light emitted from the second light source is branched into two by the beam splitter film formed on the second square prism, and the measurement surface is divided. And the reflected light reflected by the reference plane and the beams are overlapped and emitted from the beam splitter film sandwiched between the slopes of the second right-angle prism and the third right-angle prism. of Optical measuring device according to claim 1, characterized in that the formation of the optical path to be incident on the detector.   The first and second polarization preserving collimators are cased as two parallel beam collimators in which a case in which the first and second polarizers are arranged on one of the incident end side or the outgoing end side is integrated. 3. The optical system according to claim 2, wherein a retroreflector is mounted as the reference surface along with the prism unit and the first and second photodetectors on the housing. Type measuring device.

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