JP2012037461A - Optical sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sensor in which a quarter wave plate surely converts linearly polarized light into circularly polarized light to secure and maintain excellent sensor sensitivity even when a wavelength used by light source light fluctuates in an optical system in the optical sensor.SOLUTION: The optical sensor 1 for vibration detection includes a light source 2, a polarization beam splitter 3, an objective lens 4, a wave plate unit 5, and two-dimensional image sensors 6 and 14. The wave plate unit is formed of an integral structure of the quarter wave plate 7 utilizing structural birefringence and a diaphragm 8 having a reflection surface. On the light-receiving surfaces 6a and 14a of the two-dimensional image sensors, circular beam spot shapes concentric and having different radii are made incident corresponding to the position of the reflection surface 8a of the diaphragm and, from an output signal, the area or the radius of the beam spot shape is measured to detects the position or the 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 optically measuring the position, displacement, and surface roughness of an object to be measured 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.

  An optical displacement sensor that measures the surface shape and surface roughness of the measurement surface using the astigmatism method projects laser light onto the measurement surface as a minute spot, and passes the reflected light through a cylindrical lens to produce astigmatism. And the center of the beam spot is made to coincide with 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.

  As a microphone device that detects a change in sound pressure using an astigmatism method, a vibration detection device using light such as laser light is known (see, for example, Patent Document 4). In this vibration detection apparatus, linearly polarized laser light is converted into circularly polarized light by a quarter wavelength plate and reflected by the vibration plate, and reflected light is a straight line in which circularly polarized light is orthogonal to outgoing light by the quarter wavelength plate. It is converted into polarized light and detected by a quadrant photodetector. The diaphragm is placed at a position where the laser beam is focused by the focusing lens, and when the diaphragm vibrates, the deviation from the focal position is converted into an electrical signal as a change in the intensity distribution of the laser beam striking the photodetector. By doing so, sound waves are detected.

  Furthermore, an optical pressure sensor that detects the displacement of a pressure receiving element that responds to pressure in the form of an electrical signal is known (see, for example, Patent Document 5). This optical pressure sensor uses an optical system used for an optical head. Laser light is condensed and irradiated onto a diaphragm surface through a beam splitter, a quarter wavelength plate, and an objective lens, and the reflected light is reflected by a photodiode. When it is detected and deviates from the position where the diaphragm surface is completely condensed in response to the pressure, the pressure is detected from the fluctuation of the output voltage of the photodiode.

  In general, a quarter-wave plate includes a resin film made of an organic material such as polycarbonate that has been birefringent by a stretching process, a retardation plate made of a liquid crystal cell having a polymer liquid crystal layer sandwiched between transparent substrates, and a crystal. A crystal plate made of an inorganic crystal material having birefringence such as the above is used. Furthermore, a wave plate using structural birefringence due to a periodic structure with a sub-wavelength smaller than the wavelength of light to be used is known (for example, see Non-Patent Documents 1 and 2).

  This structural birefringent wave plate is characterized in that the size of the birefringence, that is, the phase difference amount and the broadband property can be controlled by selecting the dimensions of the fine periodic structure. However, if the ratio of the height to the pitch (structure period) of the convex portions forming the fine periodic structure, that is, the aspect ratio, is difficult to manufacture with high accuracy, there is a possibility that high transmittance cannot be maintained. is there. Therefore, a quarter of a combination of two wave plates in which the height of the fine periodic structure is approximately half the height required for the desired wavelength or wavelength range, with the convex portions of each periodic structure facing each other. Wave plates have been developed (for example, see Non-Patent Documents 1 and 2).

  In addition, in a quarter wavelength plate, when the reflectance of the incident surface is high or the incident angle dependency of the transmittance is large, the sensitivity decreases when used in an optical sensor, for example, due to a decrease in transmitted light intensity. There is a possibility that the recording / reproducing function is lowered in the optical pickup. Therefore, a structural birefringent wave plate in which an antireflection structure is formed on a light incident surface by forming a convex portion of a fine periodic structure in a tapered shape has been proposed (see, for example, Patent Documents 6 and 7). . Furthermore, in an optical element such as a lens, in order to suppress reflection without degrading optical performance, an antireflection film in which a large number of fine conical irregularities, for example, are formed on the incident surface at a pitch below the wavelength of light is provided. It is known (see, for example, Patent Documents 8 and 9).

  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 10). There is also known a detection device that detects a stopped state of a movable part of a mechanical facility by outputting one-dimensional or two-dimensional image data using a CCD image sensor (see, for example, Patent Document 11).

Japanese Patent Laid-Open No. 7-4914 JP-A-5-231848 JP-A-8-29664 JP 58-145299 A JP-A-1-253626 Japanese Patent No. 3913765 JP-A-2005-44429 JP 2008-197216 A JP 2009-31610 A JP 2004-354307 A JP 2003-266281 A

Makiko Imae and three others, “Optimum design of broadband quarter-wave plates using structural birefringence”, KONICA MINOLTA TECHNOLOGYREPORT, Konica Minolta Technology Center, Inc., 2006, VOL. 3, p. 62-67 Osamu Masuda, 4 others, “Creation of broadband waveplate using nanoimprint technology”, KONICA MINOLTA TECHNOLOGYREPORT, Konica Minolta Technology Center, Inc., 2008, VOL. 5, p. 101-106

  However, in the optical system of the above-described optical sensor or optical pickup, there is a possibility that the optical component is exposed to a considerably high temperature by shortening the wavelength of the semiconductor laser used as the light source or setting the operating temperature range. Therefore, an optical element used in these optical devices may be required to have sufficient heat resistance and / or light resistance.

  In addition, when a semiconductor laser is used as a light source, it may generate high heat and cause a wavelength drift of the oscillation laser. In particular, a quarter-wave plate that converts linearly polarized light into circularly polarized light causes a phase shift in the emitted light due to the wavelength drift of the laser light, and elliptically polarized light is emitted. For this reason, when used in an optical sensor, the light intensity received by the photodetector from the reflecting surface of the object to be measured is reduced, which may reduce the sensor sensitivity. Therefore, it is preferable that the quarter wavelength plate has a wider usable wavelength range so that an optical device such as an optical sensor on which the quarter wavelength plate is mounted can stably exhibit good performance.

  Furthermore, the conventional optical sensors described above have a problem that all of them have a large number of optical components, are large, and have a complicated structure and are expensive.

  Therefore, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is when the wavelength of light source light used in the optical system of the optical sensor varies due to, for example, a wavelength drift of a semiconductor laser. However, the ¼ wavelength plate can surely convert linearly polarized light into circularly polarized light so that good sensor sensitivity can be secured and maintained. It is a further object of the present invention to provide an optical sensor that can be reduced in size and cost by reducing the number of optical components and simplifying the structure.

In order to achieve the above object, an optical sensor according to the present invention collects a light source, a photodetector, a measurement object including a diaphragm, and light emitted from the light source so as to be focused on a reflection surface of the diaphragm. A first optical system that emits light, and a second optical system that condenses the reflected light from the reflecting surface on the light receiving surface of the photodetector,
The photodetector comprises an image sensor that detects a beam spot shape of the incident light incident on the light receiving surface,
A first optical system that transmits or reflects outgoing light from a light source; an objective lens that focuses the outgoing light transmitted or reflected by the polarizing beam splitter onto a reflecting surface of the diaphragm; and It consists of a quarter wave plate that is arranged on the opposite side of the polarizing beam splitter and through which the emitted light is transmitted,
The quarter-wave plate comprises a structural birefringent wave plate having a fine periodic structure in which a plurality of convex portions are arranged at a constant pitch smaller than the used wavelength of the emitted light,
The quarter-wave plate and the diaphragm are integrated.

  In this optical sensor, the first linearly polarized light separated from the light emitted from the light source by the polarization beam splitter is converged by the objective lens, converted into circularly polarized light by the quarter wavelength plate, and incident on the reflecting surface of the diaphragm. Then, the light is reflected as circularly polarized light in the reverse direction, converted again to second linearly polarized light by the quarter wavelength plate, and incident on the image sensor. The size of the beam spot shape received by the light receiving surface of the image sensor varies depending on the position of the reflecting surface of the diaphragm on the optical axis, so by detecting the change, the focal position of the reflecting surface of the diaphragm is detected. Can be obtained.

  The structural birefringent wave plate can change the phase difference amount and the broadband property depending on the dimension of the fine periodic structure. By using this for the quarter wavelength plate of the first optical system and setting its dimensions appropriately, even if the wavelength of the emitted light from the light source varies somewhat, linearly polarized light is more completely circularly corresponding to it. It can be converted to polarized light. Therefore, the optical sensor of the present invention can stably secure and maintain good sensor sensitivity.

  Furthermore, by integrating the quarter-wave plate and the diaphragm, the number of optical components is reduced as compared with the prior art, the optical path length from the diaphragm to the photodetector is shortened, and 1 / The alignment between the four-wavelength 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.

  In one embodiment, the quarter-wave plate comprises a pair of structural birefringent wave plates each having a fine periodic structure formed on one main surface of the substrate, and the pair of structural birefringent wave plates. Are arranged with the convex portions of the fine periodic structure facing each other. As a result, each structural birefringent wave plate makes the height of the convex part of the fine periodic structure about half of the height required for the desired use wavelength or use wavelength range, and reduces the aspect ratio with respect to the structure period. Because it can, it can be manufactured more easily and with high accuracy. As a result, the sensor sensitivity of the optical sensor can be stabilized and improved using a low-cost and high-performance quarter-wave plate.

  In another embodiment, the quarter-wave plate has an antireflection film having a large number of fine concavo-convex structures provided on the side opposite to the diaphragm, thereby reducing the incident angle dependency and preventing oblique incidence. However, since the high transmittance can be secured, the sensor sensitivity of the optical sensor can be further stabilized.

  Further, in an embodiment, the image sensor is a two-dimensional image sensor, and the two-dimensional image sensor is arranged so that the entire beam spot shape of the reflected light can be incident, thereby entering the two-dimensional image sensor. The area of the beam spot shape to be detected 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.

(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) The figure is sectional drawing which shows 1st Example of a wavelength plate unit, (B) The figure is a perspective view of a quarter wavelength plate. (A) The figure is sectional drawing which shows the modification of the wavelength plate unit of 1st Example, (B) The figure is the elements on larger scale which show the uneven surface of an antireflection film. Sectional drawing which shows 2nd Example of a wavelength plate unit. Sectional drawing which shows the modification of the wave plate unit of 2nd Example. Sectional drawing which shows 3rd Example of a wavelength plate unit. Sectional drawing which shows the modification of the wave plate unit of 3rd Example. 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 and a diaphragm 8 as a measurement object.

FIG. 2 (A) shows a first embodiment of the wave plate unit of the present invention. Waveplate unit 5 ₁ of this embodiment comprises a quarter-wave plate 7 made of a structural birefringent waveplate, a diaphragm 8 made of flat metal, joined together across the spacer 9 at their periphery Has been. As shown in FIG. 2B, the quarter-wave plate 7 is a fine substrate composed of a flat substrate 10 having a predetermined thickness and a large number of minute protrusions 11 formed on one main surface of the substrate. And a periodic structure 12. The convex portions 11 are arranged at a constant pitch smaller than the wavelength of the laser light output from the light source 2 or the minimum wavelength in the usable wavelength range.

For example, as described in Non-Patent Document 1, the sub-wavelength order fine periodic structure has effective refractive indexes nTE and nTM that are different in the periodic direction and the direction orthogonal thereto in the effective medium theory. This difference in the effective refractive index causes a difference in the propagation speed of light in each polarization direction, and as if it is a birefringent material, the passing light produces a phase difference and expresses a function as a wave plate. It has been known. The line width of the convex portion 11 of the fine periodic structure 12 is L, the height is H, the pitch is P, the refractive index of the material forming the fine periodic structure 12 is n ₁ , and the material filling the grooves between the convex portions 11 ( When in this embodiment the refractive index of air) and n _2, the effective refractive index of the fine periodic structure 12 nTE, nTM is represented by the following formula (1) (2).
nTE = {f · n ₁ exp2 + (1−f) · n ₂ exp2} exp (1/2) (1)
n TM = {f · n ₁ exp (−2) + (1−f) · n ₂ exp (−2)} exp (−1/2) (2)
However, f = L / P.

When the wavelength of the laser beam to be used is λ, the phase difference δ of the fine periodic structure 12 with respect to the incident wavelength λ is expressed by the following equation (3).
δ = (nTE−nTM) · H (3)
Therefore, a desired quarter-wave plate can be obtained by selecting the height H so as to satisfy δ = λ / 4 in the above equation (3).

  The quarter wavelength plate 7 having the sub-wavelength structure described above can be integrally formed by using a known material such as a nanoimprint method or precision molding, for example, using a resin material such as polyolefin, acrylic, or polycarbonate. The fine periodic structure 12 of the quarter wave plate 7 can be processed by etching an inorganic material such as a glass material.

  Moreover, the quarter wavelength plate 7 can also form the board | substrate 10 and the convex part 11 separately. For example, the fine periodic structure 12 can be formed by attaching another material on the main surface of the substrate 10 and processing the other material. Alternatively, the fine periodic structure 12 can be formed as an independent separate part and integrally coupled to the main surface of the substrate 10.

  The polarizing beam splitter 3, the objective lens 4, and the wave plate unit 5 that constitute the first optical system for condensing the laser light emitted from the light source 2 on the vibration plate 8 of the measurement object are the same orthogonal to the optical axis of the light source 2. The quarter-wave plate 7 is disposed on the optical axis x along the optical path from the light source 2 with the objective lens side. 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 19 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 driving circuit 19 is connected to the two-dimensional image sensor 6 to drive and control the CCD, and a signal processing circuit 20 is connected to process the output signal and output a displacement signal of the diaphragm 8. The signal processing circuit 20 includes, for example, a photoelectric converter, a differential amplifier, and the like. 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 19, so that the photodiode The charges are transferred to the CCD, converted into a voltage signal, and output to the signal processing circuit 20. The signal processing circuit 20 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.

FIG. 3 (A) shows a modification of the wave plate unit 5 ₁ of FIG. Waveplate unit 5 ₂ of the present embodiment, the fine periodic structure 12 of the entrance surface or the quarter-wave plate 7 in that a reflection preventing film 13 on the opposite side, different from the wavelength plate unit of Figure 2 . The antireflection film 13 is
As shown in FIG. 3B, a large number of fine projections 13a having a regular quadrangular pyramid shape are formed on the surface. Projections 13a are arranged with a small pitch than the wavelength of the incident light, thereby eliminating the abrupt change in refractive index at the interface between the antireflection film 13 with air, the effective reflection of light entering the waveplate unit 5 ₂ Is suppressed. The antireflection film 13 is manufactured, for example, by etching a transparent inorganic material substrate such as synthetic quartz glass or by molding a resin material, and is bonded to the incident surface of the quarter-wave plate 7. .

FIG. 4 shows a second embodiment of the wave plate unit of the present invention. Waveplate unit ₃ of this embodiment, 1/4 board 10 ₁ wavelength plate ₇₁ is also serves as a diaphragm of the measuring object, thereby being smaller and thinner. On the main surface of the substrate 10 ₁ on the incident side, similarly to the waveplate unit of the above embodiments, a large number of fine periodic structure 12 ₁ consisting of minute projections 11 ₁ are formed. The said fine periodic structure of the substrate 10 ₁ on the outer surface of the opposite side, the reflecting surface 8a is subjected to metal film 14 ₁ is formed. Linearly polarized incident wave plate unit ₃ is converted through the fine periodic structure 12 ₁ into circularly polarized light, is reflected further a circularly polarized light in the opposite direction at the reflection surface 8a passes through the substrate 10 ₁ .

Figure 5 shows a modification of the wave plate unit ₃ of FIG. Waveplate unit ₄ of this embodiment, similarly Although the substrate 10 _{and second} quarter-wave plate 7 ₂ also serves as the diaphragm of the measuring object, the fine periodic comprised of many minute projections 11 ₂ the structure 12 ₂ is constructed as a separate part. Substrate 10 _2, the reflection surface 8a is subjected to metal film 14 ₂ is formed on the main surface of the incident side. Fine periodic structure 12 ₂ is formed as a separate part independent, they are coupled together on the metal film 14 _2. Linearly polarized incident wave plate unit 5 ₄ is converted into circularly polarized light passes through the fine periodic structure 12 _1, is reflected as circularly polarized light opposite in reflecting surface 8a. Substrate 10 ₂ of the present embodiment can select various materials without any consideration of the optical characteristics as the material. Further, when the substrate 10 ₂ has a high reflectance becomes and the surface of a metal plate, it is possible to omit the metal film 14 _2.

FIG. 6 shows a third embodiment of the wave plate unit of the present invention. Waveplate unit _{5 5} of the present embodiment has 1/4-wavelength plate _{7 3} a pair of structural birefringence wave plate 15a, a 15b. Each of the structural birefringent wave plates 15a and 15b is configured in the same manner as the quarter wave plate 7 in FIG. 2, and has flat substrates 10 ₃ and 10 ₄ each having a predetermined thickness, and one of the main substrates. It has fine periodic structures 12 ₃ and 12 ₄ made up of a large number of fine convex portions 11 ₃ and 11 ₄ formed on the surface. Structural birefringence wave plate 15a, 15b is made to face the fine periodic structure sides, they are joined together to sandwich the spacer 9 ₁ at their periphery. At this time, the structural birefringent wave plates 15a and 15b arrange their optical axes non-parallel so that the sum of their phase differences is 90 °.

Diaphragm ₈₁ is made of a thin plate, that on one of the incident side reflecting surface 8a is formed by applying a metallic film 14 _3, the peripheral portion is thicker in a short rectangular tubular for reinforcement. Diaphragm ₈₁ is integrally joined to the outer surface of the side opposite to the 1/4 incident side of the wavelength plate 7 ₃ in the rectangular tubular portion thereof. Linearly polarized incident wave plate unit 5 ₅ is converted through the 1/4-wavelength plate 7 ₃ into circularly polarized light, it is reflected as circularly polarized light in the opposite direction by the reflection surface 8a. In the case where the diaphragm ₈₁ has a high reflectance becomes and the surface of a metallic material, it is possible to omit the metal film 14 _3.

Figure 7 shows a modification of the wave plate unit 5 ₅ of FIG. Waveplate unit 5 ₆ of this embodiment, in that the same anti-reflection film 13 and the wavelength plate unit 5 ₂ of Figure 3 is provided on the incident surface of the quarter-wave plate 7 _3, waveplate unit of FIG. 6 And different. On the surface of the antireflection film 13, a large number of fine projections 13a having a regular quadrangular pyramid shape are formed at a pitch smaller than the wavelength of the incident light, and the reflection of the incident light is effectively suppressed.

  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. 8 shows the positional relationship between the one-dimensional image sensor 16 composed of a CCD one-dimensional image sensor and the shape of the beam spot incident thereon, in comparison with the position of the two-dimensional image sensor 6. The one-dimensional image sensor 16 aligns the arrangement direction p of the photodiodes in a 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 16a. Arrange so that it does not enter. Further, when the one-dimensional image sensor 16 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 16a.

  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 16a in accordance with the position of the reflecting surface 8a of the diaphragm 8. The one-dimensional image sensor 16 receives the beam spot shape as a linear image in the radial direction not including the center of the circle. The photosensitive photodiode on the light receiving surface 16a accumulates electric charge, and is driven and controlled by the driving circuit 19. The electric charge is transferred from the photodiode to the CCD, converted into a voltage signal, and output to the signal processing circuit 20.

  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 16, the distances from the center O of the circle of each beam spot shape to the circumference, that is, 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. 9 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 19 is connected to the light source 2 and the two-dimensional image sensor 6. A signal processing circuit 20 is further connected to the two-dimensional image sensor 6. The wave plate unit 5 has the structure shown in FIG. 2, but can be used by replacing the wave plate unit shown in FIGS.

  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. A circular beam spot shape M0 concentric with the center O is projected onto the light receiving surface 6a of the two-dimensional image sensor 6.

  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 20 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, 16a ... Light-receiving surface, 7 ... 1/4 wavelength plate, DESCRIPTION OF SYMBOLS 8 ... Diaphragm, 8a ... Reflective surface, 9 ... Spacer, 10 ... Substrate, 11 ... Convex part, 12 ... Fine periodic structure, 13 ... Antireflection film, 13a ... Projection, 14 ... Reflective film, 15a, 15b ... Structural property Birefringent wave plate, 16 ... one-dimensional image sensor, 19 ... drive circuit, 20 ... signal processing circuit, 22 ... collimating lens.

Claims (5)

A measurement object including a light source, a photodetector, a diaphragm, a first optical system for condensing the emitted light from the light source so as to be focused on the reflection surface of the diaphragm, and A second optical system for collecting the reflected light on the light receiving surface of the photodetector;
The photodetector comprises an image sensor that detects a beam spot shape of the reflected light incident on the light receiving surface,
A polarizing beam splitter for transmitting or reflecting light emitted from the light source; and an objective lens for collecting the emitted light transmitted or reflected by the polarizing beam splitter on the reflecting surface of the diaphragm. A quarter-wave plate disposed on the opposite side of the polarizing beam splitter of the objective lens and transmitting the emitted light,
The quarter-wave plate comprises a structural birefringent wave plate having a fine periodic structure in which a plurality of convex portions are arranged at a constant pitch smaller than the use wavelength of the emitted light,
The optical sensor, wherein the quarter-wave plate and the diaphragm are integrated.   The quarter wave plate is composed of a pair of structural birefringent wave plates each having the fine periodic structure formed on one main surface of the substrate, and the pair of structural birefringent wave plates are mutually connected to the fine wave plate. The optical sensor according to claim 1, wherein the convex portions of the periodic structure are arranged to face each other.   3. The optical sensor according to claim 1, wherein the quarter-wave plate has an antireflection film having a large number of fine concavo-convex structures provided on a side opposite to the vibration plate.   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. 4. 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 11, wherein a radius of the optical sensor can be detected.

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