JP6410100B2 - Interferometer - Google Patents

Description

  The present invention relates to an interferometer and an optical branching element incorporated in the interferometer.

  In an interferometer, light from a light source is branched, propagated through different optical paths, and then combined again to generate interference light. Therefore, in order to configure the interferometer, a light source, a means for branching light from the light source, and a means for again synthesizing the branched light are required. Conventionally, a beam splitter or a half mirror has been used as means for branching light from a light source and means for recombining the branched light.

  In an interferometer configured to split and synthesize light using a beam splitter, the light from the light source is split into reference light and measurement light by the beam splitter, propagated through independent optical paths, and then again. It returns to the beam splitter and combines to generate interference light (see, for example, Patent Document 1).

  In an interferometer configured to split and synthesize light using a half mirror, a part of the light from the light source is reflected by the half mirror as reference light and the rest is transmitted as measurement light. Then, the measurement light reflected by the target is combined with the reference light reflected by the half mirror to generate interference light (see, for example, Patent Document 2).

JP-A-7-35506 Japanese Patent Laid-Open No. 11-83433

  However, an interferometer configured to split and synthesize light using a beam splitter has the disadvantages that the branched light propagates through independent optical paths, and thus is easily affected by disturbances and easily causes errors. . In addition, in this type of interferometer, a corner cube is used as an optical element for reflection in order to ensure angle stability of reflected light. However, when the corner cube is used, there is a drawback that the apparatus becomes large.

  On the other hand, in an interferometer configured to split and synthesize light using a half mirror, if the half mirror is not positioned accurately and installed, it will tilt between the optical axis of the measurement light and the optical axis of the reference light. This causes a drawback that an interference signal cannot be obtained efficiently.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an interferometer and an optical branching element that can perform high-precision measurement with a compact configuration and are easily assembled.

  Means for solving the problems are as follows.

  (1) An optical branch composed of a light source and a corner cube having a structure in which the apex is cut off, a part of the light from the light source is transmitted as measurement light from the top, and the rest is reflected as reference light to branch the light. Based on an element, a condensing lens that collects and interferes with reference light and measurement light, a photodetector that detects the intensity of light collected and interfered by the condensing lens, and an output of the photodetector An interferometer comprising a length measuring unit for measuring length.

  The light from the light source is branched into measurement light and reference light by the light branching element. The optical branching element is configured by a corner cube having a structure in which a vertex is cut off. When light from the light source enters the light branching element, a part of the light is transmitted through the top and the rest is reflected in the original direction. The light passing through the top is used as measurement light, and the reflected light is used as reference light. The measurement light is irradiated onto the target, and the reflected light is combined with the reference light to generate interference light. Interference light is generated through a condenser lens. The measurement light and the reference light reflected by the target enter the condenser lens, and are collected by the condenser lens and synthesized. Thereby, interference light is generated. The photodetector detects the intensity of the generated interference light. The length measuring unit measures the length based on the output of the photodetector.

  According to this aspect, since the measurement light and the reference light propagate on the same axis, it can be configured to be hardly affected by disturbance. Thereby, highly accurate measurement becomes possible. Further, since the optical path of the measurement light and the optical path of the reference light are arranged on the same axis, a compact configuration can be achieved. Further, the light branching element has the same structure as the corner cube with respect to a portion that reflects light from the light source. For this reason, even if it is a case where it inclines with respect to the optical axis of measurement light, reference light can be reflected in the same direction as the optical axis of measurement light. Thereby, the installation accuracy can be roughened and the assembly can be facilitated.

  (2) The interferometer according to (1) above, wherein the top of the light branching element is formed of a convex lens surface.

  According to this aspect, the top part of the light branching element is constituted by the convex lens surface. Thereby, the measurement light can be condensed and irradiated on the target, and the light can be used efficiently.

  (3) The light branching element is disposed coaxially with the optical axis of the light emitted from the light source, transmits light from the light source between the light source and the light branching element, and transmits reference light and measurement light. The interferometer according to (1) or (2), further comprising a beam splitter that reflects toward the photodetector, and a condensing lens disposed between the beam splitter and the photodetector.

  According to this aspect, the beam splitter is disposed coaxially with the optical axis of the light emitted from the light source. Measurement light and reference light reflected by the target propagate on the same axis as the optical axis, and are reflected in the direction of the photodetector by the beam splitter. And it injects into a photodetector through a condensing lens.

  (4) A first port, a second port, and a third port are provided. Light incident on the first port is emitted from the second port, and light incident on the second port is emitted from the third port. An optical circulator; a first optical fiber connected to the first port and propagating light from the light source to the first port; and a light connected to the second port and emitted from the second port from the fiber end; and A second optical fiber that propagates light incident on the fiber end to the second port; and a third optical fiber that is connected to the third port and propagates light emitted from the third port to the photodetector; The condensing lens and the optical branching element are coaxially arranged, and the light emitted from the fiber end of the second optical fiber enters the optical branching element through the condensing lens and is condensed by the condensing lens. The second light Enters the fiber end of Aiba, interferometer of (1) or (2).

  According to this aspect, the light from the light source is guided to the optical branching element via the optical fiber. Further, the interference light is guided to the photodetector through the optical fiber. Thereby, a light source and a measurement part (components including a condensing lens and a light branching element), a photodetector and a measurement part, a light source and a light detector can be separated from each other, and the degree of layout freedom can be improved.

  (5) An optical branching element that is incorporated in the interferometer and splits the light from the light source into the measurement light and the reference light, and is composed of a corner cube having a structure in which the apex is cut off, and a part of the incident light Is an optical branching element that transmits light from the top as measurement light, reflects the rest as reference light, and branches incident light into measurement light and reference light.

  According to this aspect, the light branching element is configured by a corner cube having a structure in which a vertex is cut off. When light from the light source enters the light branching element, a part of the light is transmitted through the top and the rest is reflected in the original direction. The light passing through the top is used as measurement light, and the reflected light is used as reference light.

  (6) The light branching element according to the above (5), wherein the top portion is constituted by a convex lens surface.

  According to this aspect, the top part of the light branching element is constituted by the convex lens surface. Thereby, measurement light can be condensed and irradiated, and light can be used efficiently.

  According to the present invention, highly accurate measurement can be performed with a compact configuration. In addition, assembly is easy.

1 is a schematic configuration diagram of a first embodiment of an interferometer according to the present invention. Perspective view of optical branching element Side view of optical branching element Front view of optical branching element Conceptual diagram of measurement light and reference light propagating in the optical path between the optical branching element and the beam splitter Schematic configuration diagram of a second embodiment of an interferometer according to the present invention Schematic configuration diagram of a third embodiment of an interferometer according to the present invention Side view of optical branching element used in interferometer of third embodiment

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<< First Embodiment >>
<Constitution>
FIG. 1 is a schematic configuration diagram of a first embodiment of an interferometer according to the present invention.

  As shown in the figure, the interferometer 10 of this embodiment includes a light source 12, a beam splitter 14, an optical branching element 16, a target 18, a photodetector 20, a condenser lens 22, and a length measuring unit 24. Configured.

  The light source 12 emits a collimated single wavelength laser beam. The light source 12 is fixedly installed at a fixed position.

  The beam splitter 14 is arranged coaxially with the optical axis L of the laser light emitted from the light source 12. The beam splitter 14 is installed in a fixed position. The beam splitter 14 transmits the laser light from the light source 12 and reflects the reference light and measurement light from the optical branching element 16 toward the photodetector 20.

  The light branching element 16 is arranged coaxially with the optical axis L of the laser light emitted from the light source 12. The optical branching element 16 is fixedly installed at a fixed position. Laser light from the light source 12 that has passed through the beam splitter 14 is incident on the optical branching element 16. The light branching element 16 branches the laser light from the light source 12 into measurement light and reference light.

  2, 3 and 4 are a perspective view, a side view and a front view of the optical branching element, respectively.

  As shown in FIGS. 2 to 4, the optical branching element 16 is configured by a corner cube prism (CCP) having a structure in which a vertex is cut off. CCP is a prism that reflects (retroreflects) light in the original direction regardless of the incident direction, and is a form of a corner cube. The CCP has three surfaces that intersect at right angles, and uses the total internal reflection of the three surfaces to fold light incident on the prism 180 degrees in the incident direction.

  The optical branching element 16 has a frustum shape as a whole, and includes an incident surface 16A, three reflecting surfaces 16B, 16C, and 16D, and a transmitting surface 16E.

  The incident surface 16A is a surface on which the laser light from the light source 12 is incident. The light branching element 16 of the present embodiment has a circular shape with a smooth incident surface 16A. The incident surface 16A is provided with an anti-reflection film (AR coat: Anti-Reflective coat).

  The three reflecting surfaces 16B, 16C, and 16D reflect (recursively reflect) part of the laser light incident on the incident surface 16A in the original direction. The three reflecting surfaces 16B, 16C, 16D are arranged at right angles to each other. A part of the laser light incident on the incident surface 16A is reflected once by the three reflecting surfaces 16B, 16C, and 16D, and then returns to the original direction.

  The transmission surface 16E is a surface that transmits part of the laser light incident on the incident surface 16A. The transmission surface 16E is disposed on the top of the light branching element 16. The transmission surface 16E has a flat triangular shape and is provided in parallel with the incident surface 16A. The transmission surface 16E is provided with an AR coat.

  The light branching element 16 is arranged coaxially with the optical axis L of the laser light emitted from the light source 12. The laser beam emitted from the light source 12 passes through the beam splitter 14 and enters the center of the incident surface 16A of the light branching element 16 perpendicularly. In the laser light incident on the incident surface 16A, the light at the central portion is transmitted through the transmission surface 16E. Then, the remainder (peripheral light) is reflected by the reflecting surfaces 16B, 16C, and 16D and folded back 180 degrees in the incident direction. Light that passes through the transmission surface 16E is measurement light, and light that is folded in the incident direction by the reflection surfaces 16B, 16C, and 16D is reference light. The measurement light and the reference light propagate in the opposite directions on the same axis.

  In this way, the optical branching element 16 branches part of the incident laser light into the measurement light and the reference light by transmitting a part of the light branching element straightly and reflecting the remaining part in the original direction. For this reason, the laser beam emitted from the light source 12 has a beam diameter sufficient to obtain reflected light (reference light).

  As shown in FIG. 1, the target 18 is disposed coaxially with the optical axis L of the laser light emitted from the light source 12. The target 18 is composed of CCP and is installed on a moving body (not shown). This moving body is provided to be movable back and forth along the optical axis L of the laser beam emitted from the light source 12. The target 18 reflects the measurement light emitted from the light branching element 16 in the original direction.

  The measurement light reflected by the target 18 propagates through the original optical path and enters the transmission surface 16E of the light branching element 16. Then, it passes through the optical branching element 16 and enters the beam splitter 14 together with the reference light.

  FIG. 5 is a conceptual diagram of measurement light and reference light propagating in the optical path between the optical branching element and the beam splitter.

  As shown in FIG. 5, the measurement light L1 and the reference light L2 propagating in the optical path between the optical branching element 16 and the beam splitter 14 are propagated in such a manner that the reference light L2 wraps the measurement light L1. Therefore, even when propagating through the same optical path, the measurement light L1 and the reference light L2 propagate through the optical path between the optical branching element 16 and the beam splitter 14 without substantially intersecting.

  The photodetector 20 receives the measurement light and the reference light reflected by the beam splitter 14 and detects the intensity thereof. The photodetector 20 is disposed on the optical path of the measurement light and the reference light reflected by the beam splitter 14, and is fixedly installed at a fixed position.

  The condenser lens 22 is disposed between the beam splitter 14 and the photodetector 20 and is fixedly installed at a fixed position. The condensing lens 22 condenses the measurement light and the reference light emitted from the beam splitter 14 and enters the photodetector 20. The measurement light and the reference light are combined by being condensed by the condenser lens 22. Thereby, interference light of measurement light and reference light is generated. Therefore, the photodetector 20 detects the intensity of the interference light between the measurement light and the reference light.

  The length measuring unit 24 analyzes the interference signal output from the photodetector 20 and measures the amount of displacement of the target 18. The length measuring unit 24 is configured by a computer. The computer functions as a length measuring unit by executing a predetermined length measuring program.

<Action>
The laser light emitted from the light source 12 passes through the beam splitter 14 and enters the light branching element 16. Part of the laser light incident on the optical branching element 16 (light at the center) passes through the transmission surface 16E as measurement light, and the rest is folded 180 degrees in the original direction as reference light.

  The measurement light transmitted through the transmission surface 16E travels straight and enters the target 18 as it is. Then, it is folded back in the original direction by the target 18 and enters the optical branching element 16 again.

  The measurement light incident on the optical branching element 16 enters the beam splitter 14 together with the reference light, and is emitted toward the photodetector 20. The measurement light and the reference light are condensed by the condenser lens 22 and enter the photodetector 20. The measurement light and the reference light are combined by being condensed by the condenser lens 22. As a result, interference light between the measurement light and the reference light is generated. Therefore, the interference light between the measurement light and the reference light is incident on the photodetector 20.

  The photodetector 20 detects the intensity of the interference light. The length measuring unit 24 measures the amount of displacement of the target 18 based on the detection output of the photodetector 20.

  According to the interferometer 10 of the present embodiment, since the measurement light and the reference light propagate on the same axis, it can be configured to be hardly affected by disturbance. Thereby, highly accurate measurement becomes possible.

  Further, since the optical path of the measurement light and the optical path of the reference light are arranged on the same axis, a compact configuration can be achieved.

  Furthermore, the optical branching element 16 has the same structure as the corner cube with respect to the portion that reflects the laser light from the light source 12, and therefore, the assembly can be facilitated. That is, the part that reflects the laser light from the light source 12 (the part that separates the reference light) has the same structure as the corner cube, so that the light branching element 16 is temporarily inclined with respect to the optical axis of the laser light. Even in this case, the reference light can always be reflected in the direction coaxial with the optical axis of the laser light. Thereby, the installation precision of the optical branching element 16 can be made rough, and the assembly of an apparatus can be made easy. In addition, it can be configured to be robust against diameter changes.

<< Second Embodiment >>
<Constitution>
FIG. 6 is a schematic configuration diagram of a second embodiment of an interferometer according to the present invention.

  As shown in FIG. 6, the interferometer 100 of the present embodiment includes a light source 112, a light propagation unit 114, an optical branching element 116, a target 118, a photodetector 120, a condenser lens 122, and a length measuring unit 124. It is prepared for.

  The light source 112 emits a single wavelength laser beam. The light source 112 is fixedly installed at a fixed position.

  The light propagation unit 114 propagates the laser light emitted from the light source 112 to the condensing lens 122 and propagates the interference light emitted from the condensing lens 122 to the photodetector 120. The light propagation unit 114 includes an optical circulator 126, a first optical fiber 128, a second optical fiber 130, and a third optical fiber 132.

  The optical circulator 126 includes three ports, a first port 126A, a second port 126B, and a third port 126C, and emits light incident on the first port 126A from the second port 126B. Further, light incident on the second port 126B is emitted from the third port 126C.

  The first optical fiber 128 is connected to the first port 126A of the optical circulator 126. The first optical fiber 128 propagates the laser light emitted from the light source 112 to the first port 126A.

  The second optical fiber 130 is connected to the second port 126 </ b> B of the optical circulator 126. The second optical fiber 130 propagates the laser light emitted from the second port 126B and emits it from the fiber end. Further, light incident on the fiber end is propagated to the second port 126B.

  The third optical fiber 132 is connected to the third port 126C of the optical circulator 126. The third optical fiber 132 propagates the light emitted from the third port to the photodetector 120.

  The fiber end of the second optical fiber 130 is fixedly installed at a fixed position. Laser light emitted from the fiber end of the second optical fiber 130 enters the light branching element 116 via the condenser lens 122. The condenser lens 122 is disposed coaxially with the optical axis L of the laser light emitted from the fiber end of the second optical fiber 130.

  The optical branching element 116 is arranged coaxially with the optical axis L of the laser light emitted from the fiber end of the second optical fiber 130. The optical branch element 116 is fixedly installed at a fixed position. The configuration of the optical branching element 116 is the same as that of the optical branching element 16 of the interferometer 10 of the first embodiment described above.

  Part of the laser light incident on the light branching element 116 is transmitted through the transmission surface, and the rest is reflected by the reflection surface and folded back 180 degrees in the original direction. The light transmitted through the transmission surface is the measurement light, and the light that is folded back in the original direction is the reference light.

  The target 118 is disposed coaxially with the optical axis L of the laser light emitted from the fiber end of the second optical fiber 130. The target 118 is composed of CCP and is installed on a moving body (not shown). This moving body is provided to be movable back and forth along the optical axis L of the laser light emitted from the fiber end of the second optical fiber 130. The target 118 reflects the measurement light emitted from the light branching element 116 in the original direction.

  The measurement light reflected by the target 118 propagates through the original optical path and enters the transmission surface of the optical branching element 116. Then, it passes through the light branching element 116 and enters the condenser lens 122 together with the reference light.

  The condensing lens 122 condenses the measurement light and the reference light and enters the fiber end of the second optical fiber 130. The measurement light and the reference light are combined by being condensed by the condenser lens 22. Thereby, interference light of measurement light and reference light is generated. Accordingly, interference light between the measurement light and the reference light is incident on the fiber end of the second optical fiber 130.

  The interference light incident on the fiber end of the second optical fiber 130 propagates through the second optical fiber 130 and enters the second port 126B of the optical circulator 126. The interference light incident on the second port 126B exits from the third port 126C and enters the third optical fiber 132. Then, the light propagates through the third optical fiber 132 and enters the photodetector 120.

  The photodetector 120 detects the intensity of the incident interference light. The length measuring unit 124 measures the amount of displacement of the target 118 based on the detection output of the photodetector 120.

<Action>
The laser light emitted from the light source 12 propagates through the first optical fiber 128 and enters the first port 126A of the optical circulator 126. The laser light incident on the first port 126A exits from the second port 126B and enters the second optical fiber 130. The laser light incident on the second optical fiber 130 propagates through the second optical fiber 130 and exits from the fiber end of the second optical fiber 130. Laser light emitted from the fiber end of the second optical fiber 130 enters the light branching element 116 via the condenser lens 122.

  Part of the laser light incident on the optical branching element 116 (light at the central portion) passes through the transmission surface as measurement light, and the remaining (light at the peripheral portion) is folded back 180 degrees in the original direction as reference light.

  The measurement light transmitted through the transmission surface goes straight as it is and enters the target 118. Then, it is folded back in the original direction by the target 118 and enters the optical branching element 116 again.

  The measurement light incident on the optical branching element 116 enters the condenser lens 122 together with the reference light. Then, the light is condensed by the condenser lens 122 and is incident on the fiber end of the second optical fiber 130. The measurement light and the reference light are combined by being condensed by the condenser lens 122. As a result, interference light between the measurement light and the reference light is generated. The interference light is incident on the fiber end of the second optical fiber 130.

  The interference light incident on the fiber end of the second optical fiber 130 propagates through the second optical fiber 130 and enters the second port 126B of the optical circulator 126. The interference light incident on the second port 126B exits from the third port 126C and enters the third optical fiber 132. Then, the light propagates through the third optical fiber 132 and enters the photodetector 120. The photodetector 120 detects the intensity of the incident interference light. The length measuring unit 124 measures the amount of displacement of the target 118 based on the detection output of the photodetector 120.

  Also in the interferometer 100 of the present embodiment, since the measurement light and the reference light propagate on the same axis, it can be configured not to be affected by disturbance. Thereby, highly accurate measurement becomes possible.

  Further, since the optical path of the measurement light and the optical path of the reference light are arranged on the same axis, a compact configuration can be achieved.

  Further, the optical branching element 116 has the same structure as the corner cube with respect to the portion that reflects the laser light from the light source 12, and therefore, the assembly can be facilitated.

  Further, according to the interferometer 100 of the present embodiment, the light source 112 and the measurement unit (components including the condensing lens 122, the light branching element 116, and the target 118), the photodetector 120, the measurement unit, and the light source 112 Since the photodetectors 120 can be separated from each other, the degree of layout freedom can be improved.

<< Third Embodiment >>
<Constitution>
FIG. 7 is a schematic configuration diagram of a third embodiment of an interferometer according to the present invention.

  As shown in FIG. 7, the interferometer 200 according to the present embodiment includes a light source 212, a light propagation unit 214, an optical branching element 216, a target 218, a photodetector 220, a condenser lens 222, and a length measuring unit 224. It is prepared for.

  The interferometer 200 of the present embodiment is different from the interferometer 100 of the second embodiment described above in the configuration of the optical branching element 216 and the target 218. Regarding the configurations of the light source 212, the light propagation unit 214, the photodetector 220, the condenser lens 222, and the length measurement unit 224, the light source 112, the light propagation unit 114, and the light propagation unit 114 of the interferometer 100 according to the second embodiment described above. Since the configuration is the same as that of the photodetector 120, the condenser lens 122, and the length measuring unit 124, only the configuration of the optical branching element 216 and the target 218 will be described here.

  FIG. 8 is a side view of an optical branching element used in the interferometer of the present embodiment.

  The light branching element 216 of the present embodiment is also composed of a CCP having a structure in which the apex is cut off, but is different from the light branching elements of the first and second embodiments in that the top is composed of a convex lens surface. To do.

  As shown in FIG. 8, the optical branching element 216 includes an incident surface 216A, three reflecting surfaces 216B, 216C, and 216D, and a transmitting surface 216E. And the transmissive surface 216E which comprises a top part is comprised by a convex lens surface.

  In the laser light incident on the incident surface 216A, the light at the central portion is transmitted through the transmission surface 216E as measurement light, and the rest is reflected as reference light on the reflection surfaces 216B, 216C, and 216D in the incident direction.

  Here, the measurement light transmitted through the transmission surface 216E is condensed and irradiated onto the target 218 when the transmission surface 216E is formed of a convex lens surface. Thereby, the measurement light can be efficiently irradiated onto the target 218.

  As shown in FIG. 7, the target 218 is formed of a rectangular plate-shaped piece. The target 218 has an irradiation surface 218A. Irradiation surface 218A is a rough surface. The target 218 is provided on a moving body (not shown). The moving body is provided to be movable back and forth along the optical axis of the measurement light. The measurement light is perpendicularly incident on the center of the irradiation surface 218A of the target 218.

<Action>
A part of the laser light incident on the incident surface 216A of the optical branching element 216 passes through the transmission surface 216E as measurement light and the rest (peripheral light) in the original direction as reference light. Folded 180 degrees.

  Here, in the light branching element 216 of the present embodiment, the transmissive surface 216E is configured by a convex lens surface. For this reason, the measurement light transmitted through the transmission surface 216E is condensed and irradiated onto the irradiation surface 218A of the target 218.

  The measurement light applied to the irradiation surface 218A of the target 218 becomes scattered light, and a part of the scattered light enters the transmission surface 216E of the light branching element 216. The scattered light of the measurement light incident on the transmission surface 216E of the light branching element 216 is emitted from the incident surface 216A of the light branching element 216 together with the reference light, and enters the condenser lens 222.

  The measurement light and the reference light incident on the condenser lens 222 are combined by being condensed by the condenser lens 222. As a result, interference light between the measurement light and the reference light is generated.

  According to the interferometer 200 of the present embodiment, the top of the light branching element 216 is configured with a convex lens surface, so that the target 218 can be efficiently irradiated with measurement light. Thereby, it is not necessary to configure the target 218 with CCP, and the configuration can be further simplified.

  In this embodiment, the case where the optical branching element and the target of the interferometer 100 of the second embodiment are changed has been described as an example. However, the optical branching element and the target of the interferometer 10 of the first embodiment are changed. Similar effects can be achieved when the optical branching element and the target of the present embodiment are changed.

<< Other Embodiments >>
<Other forms of optical branching element>
In the above embodiment, the optical branching element is configured using CCP. However, the optical branching element may be configured using a corner cube having another structure. For example, a corner cube having a structure in which three reflecting mirrors are combined at right angles can be used.

  Further, the size of the top of the light branching element (the size of the transmission surface) is appropriately set according to the beam diameter of the laser light incident on the light branching element. That is, the optical branching device of the present invention transmits a part of the light incident on the optical branching device from the top and branches it to the measurement light and the reference light, so that the top is only a part of the light incident on the incident surface. Is set to a transparent size.

As an example, consider a standard Gaussian beam whose light intensity distribution is expressed as I (r) = I ₀ exp (−2r ² / w ₀ ² ). Here, I is a light intensity, I ₀ is a constant indicating the total intensity, r is a radius from the optical axis, and w ₀ is a radius (Gaussian beam radius) at which the light intensity is 1 / e ² .

At this time, the radius of the light intensity becomes half is calculated as 0.59 W _0. Therefore, when using a light beam with a radius w ₀ , the ratio of the reference light to the measurement light (reference light: measurement) is made by making the size of the apex (area of the transmission surface) equal to the circle with a radius of 0.59 w _0. Light) can be 50:50.

  Moreover, an arbitrary branching ratio can be obtained by using an optical branching element whose top portion is changed in size as required.

<Other forms of target>
The target is not limited to CCP, but can also be configured by a reflection mirror.

<Structure of interferometer>
In the above embodiment, the case where the present invention is applied to a general single wavelength interferometer has been described as an example. However, the application of the present invention is not limited to this. In addition, for example, the present invention can also be applied to a multi-wavelength interferometer (interferometer that obtains an optical path difference using a combined wavelength of a plurality of wavelengths by scanning the wavelength of a light source).

  In the above embodiment, the case where the target provided in the moving body is irradiated with measurement light and the amount of displacement of the target is measured has been described as an example, but the measurement light is directly irradiated onto the measurement object, The same applies to measuring the distance and displacement.

  DESCRIPTION OF SYMBOLS 10 ... Interferometer, 12 ... Light source, 14 ... Beam splitter, 16 ... Optical branching element, 16A ... Incident surface, 16B ... Reflective surface, 16C ... Reflective surface, 16C ... Reflective surface, 16E ... Transmitting surface, 18 ... Target, 20 DESCRIPTION OF SYMBOLS ... Photo detector, 22 ... Condensing lens, 24 ... Measuring unit, 100 ... Interferometer, 112 ... Light source, 114 ... Light propagation part, 116 ... Optical branching element, 118 ... Target, 120 ... Photo detector, 122 ... Condensing lens, 124 ... length measuring unit, 126 ... optical circulator, 126A ... first port, 126B ... second port, 126C ... third port, 128 ... first optical fiber, 130 ... second optical fiber, 132 ... first 3 optical fibers, 200 ... interferometer, 212 ... light source, 214 ... light propagation part, 216 ... light branching element, 216A ... incident surface, 216B ... reflective surface, 216C ... reflective surface, 216D Reflecting surfaces, 216E ... transmitting surface, 218 ... target, 218A ... irradiation surface, 220 ... photodetector, 222 ... condenser lens, 224 ... measuring unit

Claims (4)

A light source;
Consists of a corner cube with the apex cut off, a part of the light from the light source is transmitted from the top as measurement light and emitted toward the target , the rest is reflected as reference light, and the light is measured A light branching element that branches into light and the reference light ;
The hollow cylindrical reference light reflected by the light branching element and the measurement light reflected by the target and transmitted through the top of the light branching element and passing through the inside of the reference light are collected. A condensing lens to interfere with,
A photodetector for detecting the intensity of the light collected and interfered by the condenser lens;
A length measuring unit for measuring length based on the output of the photodetector;
An interferometer comprising. The top part of the light branching element is constituted by a convex lens surface.
The interferometer according to claim 1. The light branching element is disposed coaxially with the optical axis of the light emitted from the light source;
A beam splitter that transmits light from the light source and reflects the reference light and the measurement light toward the photodetector between the light source and the light branching element,
The condenser lens is disposed between the beam splitter and the photodetector;
The interferometer according to claim 1 or 2. A first port, a second port, and a third port are provided. Light incident on the first port is emitted from the second port, and light incident on the second port is emitted from the third port. An optical circulator
A first optical fiber connected to the first port and propagating light from the light source to the first port;
A second optical fiber connected to the second port, emitting light emitted from the second port from a fiber end, and propagating light incident on the fiber end to the second port;
A third optical fiber connected to the third port and propagating light emitted from the third port to the photodetector;
The light collecting element and the light branching element are arranged coaxially, and light emitted from the fiber end of the second optical fiber is incident on the light branching element through the light collecting lens, And the light condensed by the condenser lens is incident on the fiber end of the second optical fiber,
The interferometer according to claim 1 or 2.

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