JP2011237271A - Optical sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve miniaturization and cost reduction in an optical sensor by reducing the number of optical components and simplifying a structure.SOLUTION: A vibration detection optical sensor 1 includes a light source 2; a polarization beam splitter 3; an objective lens 4; a wavelength plate unit 5; and a two-dimensional image sensor 6 as a light detection part. The wavelength plate unit is configured by integrating a 1/4 wavelength plate 7 with a diaphragm 8, so as to miniaturize the optical sensor, simplify the structure and assembling, and reduce a cost. Circular beam spot shapes with concentric and different radii are made incident on a light-receiving surface 6a of the two-dimensional image sensor in accordance with a position of a reflection surface 8a of the diaphragm. Areas or radii of the beam spot shapes are measured based on an output signal of the two-dimensional image sensor, so as to detect a position or displacement magnitude of the diaphragm.

Description

  The present invention relates to an optical sensor for detecting, for example, fluid pressure and sound pressure, displacement of a measurement surface, vibration, and the like.

  Conventionally, in an optical pickup for reproducing or recording information from an optical disk such as a CD, a knife edge method, an astigmatism method, a critical angle method, Optical methods such as Foucault method are adopted. Various methods and apparatuses for measuring the position, displacement, and surface roughness of a measurement object using these techniques have been proposed.

  For example, in order to measure a minute displacement or surface roughness of an object using the knife edge method, a laser beam is projected onto a measurement object so as to be focused on the surface, and the reflected light is received by a two-divided diode. A measuring instrument is known (see, for example, Patent Document 1). In this optical system, a knife edge is arranged in the middle of the optical path, and the cross section of the reflected beam incident on the two-divided diode becomes a semicircle. When the surface of the object to be measured is shifted backward from the focal position, the reflected beam is shifted downward from the two-divided diode, and when it is shifted forward, it is shifted upward. The displacement amount of the object surface can be obtained.

  Also, an optical displacement sensor that measures the surface shape and surface roughness of the measurement surface using the astigmatism method projects the laser beam as a minute spot onto the measurement surface, and passes the reflected light through a cylindrical lens. A point aberration is given, and the center of the beam spot is made incident on the center of the four-divided light receiving element (see, for example, Patent Documents 2 and 3). When the measurement surface is at the focal position of the laser beam, the output signal of each light receiving element is equal, but when the measurement surface is shifted backward or forward, the output signal of the light receiving element at one diagonal position is the other diagonal. It becomes larger than the output signal of the light receiving element at the position. Therefore, by calculating the displacement signal of the measurement surface from the output signal of each light receiving element, the displacement amount from the focal position of the measurement surface can be obtained.

  Further, a dimension measuring device using a one-dimensional image sensor such as a CCD image sensor or a CMOS image sensor as a photodetector is known (see, for example, Patent Document 4). Also, a detection device that detects a stop state of a movable part of a mechanical facility by outputting one-dimensional or two-dimensional image data using a CCD image sensor is known (see, for example, Patent Document 5).

Japanese Patent Laid-Open No. 7-4914 JP-A-5-231848 JP-A-8-29664 JP 2004-354307 A JP 2003-266281 A

  However, each of the above-described conventional optical sensors has a problem that the number of optical components is large, the size is large, and the structure is complicated and expensive.

  Accordingly, the present invention has been made in view of the above-described conventional problems, and an object thereof is to reduce the number of optical components, simplify the structure, and realize light that can be downsized and reduced in cost. To provide a sensor.

  In order to achieve the above object, the optical sensor of the present invention includes a light source, a photodetector, and a first optical system that condenses the emitted light from the light source so as to be focused on the reflection surface of the measurement object; A second optical system for condensing the reflected light from the reflecting surface on the light receiving surface of the photodetector, the photodetector comprising an image sensor, and detecting a beam spot shape of the reflected light incident on the image sensor. It is characterized by that.

  The size of the beam spot shape on the light receiving surface of the image sensor varies depending on the position of the reflection surface of the measurement object on the optical axis. Therefore, since the size of the beam spot shape detected from the image sensor changes corresponding to the displacement of the reflecting surface from the in-focus position, the amount of displacement of the reflecting surface of the measurement object is detected by detecting this change. Can be requested.

  In an embodiment, the image sensor is a two-dimensional image sensor, and the two-dimensional image sensor is arranged so that all of the reflected beam spot shape can be incident, whereby the beam incident on the two-dimensional image sensor. The area of the spot shape can be detected. Since the size of the beam spot shape varies depending on the position of the reflecting surface, the position of the reflecting surface is measured from the area of the beam spot shape.

  In another embodiment, the image sensor is a one-dimensional image sensor, and the one-dimensional image sensor is arranged in alignment with the radial direction of the beam spot shape of the reflected light, and thereby the beam spot incident on the one-dimensional image sensor. The radius of the shape can be detected. Each beam spot shape is projected onto concentric circles sharing the center, and the positions of the circumferences thereof vary depending on the position of the reflecting surface, and therefore the position of the reflecting surface is measured from the radius of the beam spot shape. In addition, since the one-dimensional image sensor has a small light receiving area, the entire sensor can be miniaturized.

  In one embodiment, the first optical system includes a polarizing beam splitter that transmits or reflects light emitted from a light source, an objective lens that focuses the emitted light on a reflection surface of a measurement object, and a polarized beam of the objective lens. A quarter wave plate disposed on the opposite side of the splitter. As a result, the first linearly polarized light separated by the polarization beam splitter is converged by the objective lens, and is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate, and reflected from the measurement object. The light is incident on the surface, is reflected as circularly polarized light in the reverse direction, is again converted into second linearly polarized light by the quarter-wave plate, and is incident on the photodetector.

  In another embodiment, the optical sensor can further be provided with a diaphragm as a measurement object, so that it can be used to measure vibration due to fluid pressure or sound pressure.

  According to still another embodiment, the quarter wavelength plate and the diaphragm are integrated, so that the number of optical components is reduced as compared with the prior art, and the optical path length from the diaphragm to the photodetector is shortened. In addition, when the optical sensor is assembled, the alignment between the quarter-wave plate and the diaphragm can be omitted, and the alignment between them and the other optical system can be completed only once. Therefore, the entire apparatus can be miniaturized, the structure and assembly can be simplified, and a more accurate and reliable optical sensor can be obtained at low cost.

(A) is a block diagram of the first embodiment of the optical sensor according to the present invention, (B) is a diagram showing the beam shape on the two-dimensional image sensor. (A)-(F) figure is sectional drawing which shows the structure of a wavelength plate unit from which each differs. The figure which shows the beam shape on a one-dimensional image sensor in a modification. (A) is a block diagram of a second embodiment of the optical sensor according to the present invention, and (B) is a diagram showing a beam shape on the two-dimensional image sensor.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are denoted by the same or similar reference numerals.

  FIG. 1A shows the configuration of the first embodiment of the optical sensor according to the present invention. The optical sensor 1 of the present embodiment is for detecting vibrations, and includes a light source 2 composed of a laser diode, a flat polarizing beam splitter 3, an objective lens 4, a wave plate unit 5, and light detection. And a two-dimensional image sensor 6 as a unit. The wave plate unit 5 is a unitary combination of a quarter wave plate 7 made of a quartz plate and a metal diaphragm 8. The quarter-wave plate 7 and the diaphragm 8 are formed such that the peripheral edge portion on one side is thick in a short cylindrical shape for reinforcement, and the short cylindrical portions are butted together and joined together.

  The polarizing beam splitter 3, the objective lens 4, and the wave plate unit 5 are arranged on the same optical axis x orthogonal to the optical axis of the light source 2, with the quarter wavelength plate 7 along the optical path from the light source 2 on the objective lens side. Arranged. The two-dimensional image sensor 6 is arranged on the opposite side of the wave plate unit 5 with the polarization beam splitter 3 sandwiched on the same optical axis x.

  The light source 2 is connected to a drive circuit 9 that is a power source and controls the output of the emitted laser light. The two-dimensional image sensor 6 of the present embodiment is a CCD two-dimensional image sensor in which a large number of photodiodes and CCDs are arranged in a grid pattern, for example. A drive circuit 9 is connected to the two-dimensional image sensor 6 to drive and control the CCD, and a signal processing circuit 10 is connected to process the output signal and output a displacement signal of the diaphragm 8. The signal processing circuit 10 includes, for example, a photoelectric converter and a differential amplifier. In another embodiment, a CMOS image sensor can be used for the two-dimensional image sensor 6.

  In the optical sensor 1, the divergent laser light L emitted from the light source 2 is reflected by the polarizing beam splitter 3 with the S-polarized linearly polarized light component, converged by the objective lens 4, and enters the wave plate unit 5. The laser light L incident on the wave plate unit is converted from linearly polarized light to circularly polarized light when passing through the quarter wave plate 7 and projected on the surface of the vibration plate 8 to be reflected as circularly polarized light in the reverse direction. Is done. The reflected light from the surface of the diaphragm 8 passes through the quarter-wave plate 7 again, is converted to P-polarized linearly polarized light, is converged by the objective lens 4, passes through the polarizing beam splitter 3, and is reflected on the optical axis x. An image is formed, diffused, and incident on the two-dimensional image sensor 6.

  FIG. 1B shows the shape of the beam spot incident on the light receiving surface 6 a of the two-dimensional image sensor 6. When the diaphragm 8 is in the non-displacement state shown in FIG. 1A, the reflecting surface 8a is located at the position S0 and the laser beam L is focused on the reflecting surface. At this time, the reflected light R0 from the reflecting surface 8a follows the same optical path as that at the time of incidence, reaches the polarization beam splitter 3 with the same beam cross section as that at the time of incidence, passes through this, and forms an image on the optical axis x. , Enters the two-dimensional image sensor 6. A circular beam spot shape m0 concentric with the center O is projected onto the light receiving surface 6a.

  When the diaphragm 8 is displaced from the non-displacement position S0 toward the optical axis direction, that is, to the position S1 on the ¼ wavelength plate 7 side, the laser light L is reflected on the reflection surface 8a before the focal position S0. Therefore, the reflected light R1 follows the optical path from the reflecting surface to the inside of the incident light, reaches the polarization beam splitter 3 with a beam cross section somewhat narrower than that at the incident time, passes through this, and is connected on the optical axis x. After imaging, the light enters the two-dimensional image sensor 6. The imaging position of the reflected light R1 is in front of the reflected light R0, that is, on the polarizing beam splitter 3 side. In this case, the projected beam spot shape m1 is concentric with the original beam spot shape m0 and becomes a larger circle.

  When the diaphragm 8 is displaced from the non-displacement position S0 to the rear side in the optical axis direction, that is, to the position S2 on the opposite side of the quarter wavelength plate 7, the laser light L is reflected to the reflecting surface 8a behind the focal position S0. For this reason, the reflected light R2 follows the optical path from the reflection surface to the outside of the incident light, reaches the polarization beam splitter 3 with a beam cross section somewhat thicker than the incident light, passes through this, and is connected on the optical axis x. After imaging, the light enters the two-dimensional image sensor 6. The imaging position of the reflected light R2 is behind the reflected light R0, that is, on the two-dimensional image sensor 6 side. In this case, the projected beam spot shape m2 is a concentric circle smaller than the original beam spot shape m0.

  In the two-dimensional image sensor 6 that has received the reflected light, each photodiode within the range of the beam spot shape on the light receiving surface 6a is exposed and accumulates electric charge, and is driven and controlled by a drive circuit 9, so that the photodiode The charge is transferred to the CCD, converted into a voltage signal, and output to the signal processing circuit 10. The signal processing circuit 10 processes the signal output from the two-dimensional image sensor 6 and measures the area (or radius) of the circular beam spot shape projected on the light receiving surface 6a. As described above, since the size of the beam spot shape varies depending on the position of the reflecting surface 8a, that is, the diaphragm 8, by comparing the measured value with the area (or radius) of the beam spot shape m0 as a reference value, The position and / or displacement amount of the diaphragm 8 can be detected.

  In the optical sensor 1 of this embodiment, the number of optical components is significantly smaller than that of the conventional one. In addition, by using the wave plate unit 5 in which the quarter wave plate 7 and the vibration plate 8 are integrated, the optical path length from the vibration plate 8 to the two-dimensional image sensor 6 can be significantly shortened. Further, when the optical sensor 1 is assembled, it is not necessary to align the quarter-wave plate 7 and the diaphragm 8, and the alignment between them and the objective lens 4 can be performed only once. As a result, the entire apparatus can be downsized, the assembly of the optical sensor 1 can be simplified, and a highly accurate and reliable apparatus can be obtained at a lower cost.

2A to 2F show wave plate units having various structures different from those of the first embodiment. Waveplate unit 5 ₁ of FIG. 2 (A) is a combination of the diaphragm ₈₁ of the non-metal in the same quarter-wave plate 7 and the first embodiment. Diaphragm ₈₁ is made of a thin plate of glass or quartz or the like, the peripheral portion of one surface side is formed thickly short cylindrical for reinforcement. One side of the quarter-wave plate 7 side of the diaphragm _81, the reflective surface is subjected to metal film is formed. Diaphragm ₈₁ is joined together against the 1/4-wavelength plate 7 a short cylindrical portion together.

Waveplate unit 5 ₂ in FIG. 2 (B) is a combination of the diaphragm ₈₂ of thin tabular same quarter-wave plate 7 and the first embodiment. The diaphragm ₈₂ is a metal plate, is formed of a non-metallic plate such as a hard film or a glass plate. When the diaphragm ₈₂ is such as rigid film or glass plate, the reflecting surface is subjected to metal film is formed on one side of the quarter-wave plate 7 side. The diaphragm ₈₂ is bonded together with 1/4-wave plate 7 in its short cylindrical portion.

Waveplate unit ₃ in FIG. 2 (C) are those in the quarter-wave plate ₇₁ of thin tabular combining same diaphragm 8 in the first embodiment. Quarter-wave plate ₇₁ is formed, for example, a film-like resin material plate. Quarter-wave plate ₇₁ is joined integrally with the diaphragm 8 at the short cylindrical portion.

Figure 2 waveplate unit _{5 4} (D) is a combination of a waveplate unit _{5 1} 3 1/4 wave plate ₇₁ of (C) and FIG. 3 (A). 1/4 wavelength plate ₇₁ and the wavelength plate unit 5 _1, are joined together by butt short cylindrical portion together.

The wave plate unit 5 of the first embodiment and the wave plate units 5 _{1 to} 5 ₄ of FIGS. 2A to 2D are preferably provided with antireflection films on both sides of the quarter wave plate, respectively. . Further, the 1/4 the outer surface of the wave plate 7, 7 _1, can be attached to a thin glass plate 11. By this glass plate 11, the quarter-wave plate can be reinforced to relieve the stress received from the antireflection film and to eliminate the influence of vibration from the diaphragm.

Waveplate unit _{5 5} in FIG. 2 (E) is 1/4-wavelength plate _{7 2} also serves as a diaphragm. Quarter-wave plate 7 _2, as in the first embodiment, consists of a quartz plate, the peripheral portion of one surface side is formed thickly short cylindrical for reinforcement. Quarter-wave plate 7 ₂ of the outer surface i.e. said one side of the short cylindrical portion opposite subjected to metal film, reflective surface is formed. The 1/4 inner surface of the wave plate 7 _2, it is preferable that anti-reflection film.

Waveplate unit _{5 6} of FIG. 2 (F), similar to FIG. 2 (E), 1/4-wavelength plate _{7 3} also serves as a diaphragm. Quarter-wave plate 7 ₃ are formed of the same resin material plate and FIG. 2 (C), the subjected to metal film on the outer surface thereof, the reflecting surface is formed. The inner surface of the quarter-wave plate 7 _3, it is preferable to an antireflection film.

Also, 1/4-wave plate 7, 7 ₂ is preferably formed by a quartz plate of excellent X-cut or Y-cut to the input angle dependence. Furthermore, 1/4-wave plate 7, 7 _2, by a fundamental wave (zero-order) mode, excellent wavelength dependence is obtained.

  In the modification of the first embodiment, a one-dimensional image sensor can be used as the light detection unit instead of the two-dimensional image sensor 6. One-dimensional image sensors include, for example, a CCD one-dimensional image sensor in which a large number of photodiodes are arranged in a line and a CCD is arranged in parallel therewith. In another embodiment, a CMOS image sensor can be used as the two-dimensional image sensor 6.

  FIG. 3 shows the positional relationship between the one-dimensional image sensor 14 composed of a CCD one-dimensional image sensor and the shape of a beam spot incident thereon, in comparison with the position of the two-dimensional image sensor 6. The one-dimensional image sensor 14 aligns the arrangement direction p of the photodiodes in the radial direction from the circular center O (optical axis x) of the beam spot shape, and the center O (optical axis x) is the light receiving surface 14a. Arrange so that it does not enter. Further, when the one-dimensional image sensor 14 is arranged in this way, the size is selected so that the circular outline of the beam spot shape, that is, the circumference always enters the light receiving surface 14a.

  As described above in the first embodiment, circular beam spot shapes m0, m1, and m2 having different radii are projected onto the light receiving surface 14a in accordance with the position of the reflecting surface 8a of the diaphragm 8. The one-dimensional image sensor 14 receives the beam spot shape as a linear image in a radial direction not including the center of the circle. The photosensitive photodiode on the light receiving surface 6a accumulates electric charge and is driven and controlled by the driving circuit 9. The electric charge is transferred from the photodiode to the CCD, converted into a voltage signal, and output to the signal processing circuit 10.

  Since each beam spot shape m0, m1, m2 forms a concentric circle sharing the center O, the position of the circumference thereof varies depending on the position of the reflecting surface 8a, that is, the diaphragm 8. In this embodiment, by processing the signal input from the one-dimensional image sensor 14, the distances from the circular center O to the circumference of each beam spot shape, that is, the radii r0, r1, and r2 are measured. The position and / or displacement amount of the diaphragm 8 can be detected by comparing the measured value with the radius r0 when the reflecting surface 8a is at the non-displacement position S0.

  FIG. 4 shows the configuration of a second embodiment of the vibration detecting photosensor according to the present invention. The optical sensor 21 of the present embodiment is a two-dimensional light source 2 composed of a laser diode, a flat polarizing beam splitter 3, an objective lens 4, a wave plate unit 5, and a light detection unit arranged in the same manner as the first embodiment. In addition to the image sensor 6, a collimator lens 22 is further provided between the light source 2 and the polarization beam splitter 3 on the same optical axis. A drive circuit 9 is connected to the light source 2 and the two-dimensional image sensor 6. A signal processing circuit 10 is further connected to the two-dimensional image sensor 6. Instead of the wave plate unit 5, the wave plate units of FIGS. 2A to 2F can be used.

  In the optical sensor 21, the laser light L emitted from the light source 2 is converted into parallel light by the collimating lens 22, the S-polarized linearly polarized component is reflected by the polarization beam splitter 3, and converged by the objective lens 4 to be converged by the wave plate unit. 5 is incident. The laser light L incident on the wave plate unit is converted from linearly polarized light to circularly polarized light when passing through the quarter wave plate 7 and projected on the surface of the vibration plate 8 to be reflected as circularly polarized light in the reverse direction. Is done. The reflected light from the surface of the diaphragm 8 passes through the quarter-wave plate 7 again and is converted into P-polarized linearly polarized light, converted into parallel light by the objective lens 4, and transmitted through the polarizing beam splitter 3 to form a two-dimensional image. It enters the sensor 6.

  The diaphragm 8 is arranged so that the laser light L is focused on the reflecting surface 8a when the diaphragm 8 is in a non-displaced state. At this time, the reflected light R0 from the reflecting surface 8a follows the same optical path as that at the time of incidence, maintains the same beam cross section as that at the time of incidence, passes through the objective lens 4 and the polarization beam splitter 3, and becomes a two-dimensional image as parallel light. It enters the sensor 6. The beam spot shape incident on the light receiving surface 6a of the two-dimensional image sensor 6 is projected as a circular beam spot shape M0 concentric with the center O thereof.

  When the diaphragm 8 is displaced from the non-displacement position S0 toward the optical axis direction, that is, to the position S1 on the ¼ wavelength plate 7 side, the laser light L is reflected on the reflection surface 8a before the focal position S0. The reflected light R1 follows the inner optical path from the time of incidence, passes through the objective lens 4 and the polarizing beam splitter 3 with a beam cross section somewhat narrower than that at the time of incidence, and enters the two-dimensional image sensor 6 as parallel light. In this case, the projected beam spot shape M1 is a concentric circle smaller than the original beam spot shape M0.

  When the diaphragm 8 is displaced from the non-displacement position S0 to the rear side in the optical axis direction, that is, to the position S2 on the opposite side of the quarter wavelength plate 7, the laser light L is reflected to the reflecting surface 8a behind the focal position S0. The reflected light R2 follows an optical path outside the incident time, passes through the objective lens 4 and the polarization beam splitter 3 with a beam cross section somewhat thicker than the incident light, and enters the two-dimensional image sensor 6 as parallel light. In this case, the projected beam spot shape M2 is concentric with the original beam spot shape M0 and becomes a larger circle.

  Also in the present embodiment, the size of the beam spot shape incident on the light receiving surface of the two-dimensional image sensor 6 varies depending on the position of the diaphragm 8 as described above. The signal processing circuit 10 processes the signal output from the two-dimensional image sensor 6 and measures the area (or radius) of the circular beam spot shape projected on the light receiving surface 6a. Therefore, the position and / or displacement amount of the diaphragm 8 can be detected by comparing the measured value with the area (or radius) of the beam spot shape M0 as a reference value.

  Also in the present embodiment, the number of optical components is significantly reduced as compared with the prior art. Further, the wavelength plate unit 5 in which the quarter wavelength plate 7 and the diaphragm 8 are integrated can significantly shorten the optical path length from the diaphragm 8 to the two-dimensional image sensor 6. The alignment between the four-wavelength plate 7 and the diaphragm 8 is not necessary, and the alignment between them and the objective lens 4 can be performed only once. Therefore, the entire apparatus can be miniaturized, the structure and the assembly can be simplified, and a more accurate and reliable optical sensor can be obtained at a lower cost.

  Each of the above embodiments is an optical sensor for vibration detection, and is provided with a diaphragm for this purpose. However, the present invention can be used to measure the position and displacement of the measurement object separate from the optical sensor, the vibration of the surface to be measured, and the like. In that case, the wave plate unit may be replaced with a single quarter wave plate, the vibration plate may be omitted, and the laser light may be set to be focused on the surface to be measured of the measurement object.

  Various configurations other than the above-described embodiments are conceivable as an optical system for condensing and projecting laser light on a diaphragm and an optical system for causing reflected light from the diaphragm to enter a two-dimensional image sensor. For example, the linearly polarized component of the laser light emitted from the light source and transmitted through the polarizing beam splitter can be projected onto the diaphragm, and the reflected light can be reflected by the polarizing beam splitter and incident on the photodetector. .

  The present invention is not limited to the above embodiments, and can be implemented with various modifications or changes within the technical scope thereof. For example, in the first and second embodiments, as long as the displacement of the diaphragm can be detected as a change in the amount of light, the light detection unit can be configured with a plurality of two-dimensional image sensors. The polarizing beam splitter can be a prism type. Various known light sources other than the laser diode can be used as the light source.

DESCRIPTION OF SYMBOLS 1,21 ... Optical sensor, 2 ... Light source, 3 ... Polarizing beam splitter, 4 ... Objective lens, 5 ... Wave plate unit, 6 ... Two-dimensional image sensor, 6a, 14a ... Light-receiving surface, 7 ... 1/4 wavelength plate, DESCRIPTION OF SYMBOLS 8 ... Diaphragm, 8a ... Reflecting surface, 9 ... Drive circuit, 10 ... Signal processing circuit, 11 ... Glass plate, 14 ... One-dimensional image sensor, 22 ... Collimating lens.

Claims (6)

A light source, a light detector, a first optical system that focuses light emitted from the light source so as to be focused on the reflection surface of the measurement object, and light reception by the light detector from the reflection surface A second optical system for focusing on the surface,
The optical sensor comprises an image sensor, and detects a beam spot shape of the reflected light incident on the image sensor.   The image sensor is a two-dimensional image sensor, and the two-dimensional image sensor is arranged to be able to enter all of the beam spot shape of the reflected light, and thereby the beam spot incident on the two-dimensional image sensor. The optical sensor according to claim 1, wherein an area of the shape can be detected.   The image sensor is a one-dimensional image sensor, and the one-dimensional image sensor is arranged in alignment with a radial direction of the beam spot shape of the reflected light, and thereby the beam spot shape incident on the one-dimensional image sensor. The optical sensor according to claim 1, wherein the radius can be detected.   The first optical system transmits or reflects the outgoing light from the light source, an objective lens that condenses the outgoing light on the reflecting surface of the diaphragm, and the polarizing beam splitter of the objective lens 4. The optical sensor according to claim 1, comprising a quarter-wave plate disposed on the opposite side of the optical sensor.   The optical sensor according to claim 1, further comprising a diaphragm as the measurement object.   6. The optical sensor according to claim 5, wherein the quarter-wave plate is integrated with the diaphragm.

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