JP2012037733A - Optical sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly convert linear polarized light into circular polarized light, even when a one-quater wavelength plate generates phase deviation on emission light in an optical system of an optical sensor.SOLUTION: A vibration detecting optical sensor 1 comprises a light source 2, a polarized light beam splitter 3, an objective lens 4, a wavelength plate unit 5, and two-dimensional image sensors 6 and 14. In the wavelength plate unit, a one-quater wavelength plate 7, a vibration plate 8, and a phase correcting element 9 are integrated. When phase deviation is generated in emission light of the on-quater wavelength plate, the phase correcting element made from a liquid crystal layer 13 put between transparent substrates applies voltage corresponding to action temperature on the liquid crystal layer to change a retardation value, thereby converting the linear polarized light into the perfect circular polarized light. In the two-dimensional image sensors 6 and 14, circular beam spot shapes which are concentric and have different radii are emitted on light receiving surfaces 6a and 14a so as to correspond to a position of a reflecting surface 8a of the vibrating plate. The areas or radii of the beam spot shapes are measured from output signals thereof to detect the position or the displacement amount of the vibrating plate.

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. As a birefringent crystal plate, the incident angle dependency is improved by making the refraction direction of extraordinary light determined by the incident angle of light coincide with the crystal axis other than the optical axis and orthogonal to the optical axis. It is known that linearly polarized light that is always converted into circularly polarized light and then emitted (see, for example, Patent Document 6).

  As a retardation plate composed of a liquid crystal cell with a liquid crystal layer sandwiched between two transparent substrates, liquid crystal molecules are arranged substantially in one direction in a plane parallel to the transparent substrate, and are parallel and transparent to the arrangement direction. In the plane perpendicular to the substrate, there are liquid crystal molecules arranged in the center between the two transparent substrates so as to be substantially parallel to the transparent substrate and to be inclined with a large pretilt angle as the distance from the transparent substrate becomes closer. (For example, see Patent Document 7). By aligning the liquid crystal molecules in this way, a quarter-wave plate in which the incident angle dependence of the phase difference is symmetric with respect to the center position of the liquid crystal layer in the vertical direction of the transparent substrate can be obtained.

  Moreover, even when the polarization direction of the linearly polarized light emitted from the semiconductor laser light source fluctuates due to a temperature rise during operation, the linearly polarized light having a constant polarization direction can always be emitted by the combination of the quarter wavelength plate and the liquid crystal cell. A liquid crystal element has been proposed (see, for example, Patent Document 8). In the liquid crystal cell of this liquid crystal element, the optical axis of the liquid crystal layer is set at an angle of about 45 ° with respect to a specific direction in the plane of the plate on which the optical axis of the quarter wave plate is directed, and the retardation value of the liquid crystal layer is set. By changing between λ (wavelength) and 0 according to the applied voltage, linearly polarized light having an arbitrary polarization direction can be converted into linearly polarized light having the polarization direction of the specific direction and emitted.

  Furthermore, in an optical head device using a polarization optical system, the phase of both linearly polarized light whose polarization directions are orthogonal to each other, such as light incident on the optical recording medium and light reflected from the optical recording medium. There is known a phase correction element capable of correcting the above with a single liquid crystal layer (see, for example, Patent Document 9). In this phase correction element, the major axis direction of the liquid crystal molecules is substantially parallel to the substrate surface between two opposing transparent substrates and is continuously twisted by 90 ° from one transparent substrate toward the other transparent substrate. When twisted nematic liquid crystal in an aligned state is used for the liquid crystal layer and a predetermined voltage is applied to the liquid crystal layer, the liquid crystal molecules rise substantially vertically in the intermediate region between the two substrates and are effectively two orthogonally aligned liquid crystals Configured to have layers.

  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 Publication No. 3-58081 JP 2006-40343 A JP 2007-333945 A JP 2007-157235 A JP 2004-354307 A JP 2003-266281 A

  However, semiconductor lasers used as light sources for the optical sensors and optical pickups mentioned above have a drift in the wavelength of the oscillation laser when operating at high temperatures, and the high temperature of the laser light directly affects the optical components of the optical system used. There is a risk of affecting. In particular, a quarter-wave plate that converts linearly polarized light into circularly polarized light emits elliptically polarized light when a phase shift occurs in the emitted light due to a wavelength drift of the laser light or a high temperature. For this reason, the light intensity received from the reflection surface of the measurement object by the photodetector of the optical sensor may be reduced, and the sensor sensitivity may be reduced.

  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.

  Accordingly, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to phase the light transmitted through the quarter-wave plate in the optical system of the optical sensor due to, for example, fluctuations in operating temperature. To provide an optical sensor that can surely convert linearly polarized light into circularly polarized light even when deviation occurs, reduce the number of optical components and simplify the structure, and realize downsizing and cost reduction. is there.

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 consists of an image sensor that detects the beam spot shape of the reflected 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 A quarter-wave plate that is disposed on the opposite side of the polarization beam splitter and transmits outgoing light, and a phase correction element for adjusting the phase of outgoing light that passes through the quarter-wave plate,
The quarter-wave plate, the phase correction element, 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.

  By providing a phase correction element in the first optical system of such an optical sensor, even when a phase shift occurs in the light transmitted through the quarter-wave plate, linearly polarized light can be reliably converted into circularly polarized light. In the image sensor, the possibility that the intensity of light received from the reflection surface of the diaphragm is reduced is eliminated, and good sensor sensitivity can be secured and maintained. Further, by integrating the phase correction element, the quarter wavelength plate, and the diaphragm, 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. The alignment of the / 4 wavelength plate, the vibration plate, and the phase correction element 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 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 optical sensor further includes a temperature sensor for determining an adjustment amount of the phase of the emitted light by the phase correction element. Thereby, for example, the phase shift of the output light generated in the quarter-wave plate due to the wavelength drift due to the high temperature of the laser light or the fluctuation of the operating temperature can be eliminated.

  In another embodiment, the temperature sensor is provided integrally with the quarter-wave plate, so that the phase shift of the output light generated in the quarter-wave plate due to the fluctuation of the operating temperature can be more reliably performed. Can be resolved.

  In yet another embodiment, the temperature sensor comprises a tuning fork type piezoelectric vibrator. As a result, a temperature sensor that exhibits frequency characteristics that change almost linearly with respect to temperature within the operating temperature range of the optical sensor can be obtained relatively easily and 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. Sectional drawing which shows 1st Example of a wavelength plate unit. Sectional drawing which shows 2nd Example of a wavelength plate unit. (A)-(F) figure is sectional drawing which shows the structure of a different wavelength plate unit, respectively. Sectional drawing which shows 3rd Example of a wavelength plate unit. (A) The figure is sectional drawing which shows 4th Example of a wavelength plate unit, (B) The figure is a top view which shows the temperature sensor element used for it. 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, a metal diaphragm 8 as a measurement object, and a phase correction element 9.

  FIG. 2 shows a first embodiment of the wave plate unit 5. The phase correction element 9 is composed of a liquid crystal cell composed of a liquid crystal layer 13 that is sandwiched between a pair of transparent substrates 10 and 11 and sealed with a seal 12. Transparent electrodes 14 and 15 are formed on opposing surfaces of the transparent substrates 10 and 11, respectively, and alignment films 16 and 17 are formed thereon. The transparent electrodes 14 and 15 are connected to an AC power source 18. The quarter-wave plate 7 and the diaphragm 8 are each formed thickly in a rectangular tube with a short peripheral edge on one side for reinforcement, and each rectangular tube portion is formed on the outer surface of the transparent substrate of the phase correction element 9. Butt and joined together.

The liquid crystal layer 13 is made of nematic liquid crystal, and is aligned by the alignment films 16 and 17 so that the major axes of the liquid crystal molecules are aligned in a certain direction between the transparent substrates when the voltage applied to the transparent electrode is zero. The liquid crystal layer 13, the and the liquid crystal layer thickness (difference between the extraordinary refractive index n _e and ordinary index n _o) the magnitude of the birefringence [Delta] n of the liquid crystal layer when a d, the retardation value R is as [Delta] n · d Defined. The retardation value R of the liquid crystal layer changes according to the voltage applied from the AC power supply 18.

  When a liquid crystal having a positive dielectric anisotropy Δε is used for the liquid crystal layer 13, the alignment direction of the liquid crystal molecules is aligned with a direction that forms an angle of 45 ° with the X axis in the XY plane when the applied voltage is zero. Here, the XY plane is a plane parallel to the substrate surface of the transparent substrate, and the X-axis direction coincides with the direction of the optical axis of the quarter-wave plate 7. In the liquid crystal layer 13, as the voltage applied to the transparent electrode increases, the alignment direction of the liquid crystal molecules rises in a direction perpendicular to the substrate surface of the transparent substrate, and the retardation value R changes from λ to 0.

  The voltage applied to the liquid crystal layer 13 is a magnitude necessary to eliminate the phase shift by measuring the phase shift of the emitted light generated by the quarter-wave plate 7 due to fluctuations in the operating temperature by experiment or simulation. Is determined in advance. In use, the operating temperature of the optical sensor 1 is measured by a separate temperature sensor, and an applied voltage corresponding to the measured value is supplied from the AC power supply 18 to the transparent electrode of the phase correction element 9. As a result, the wave plate unit 5 can reliably convert linearly polarized light into circularly polarized light by the phase correction element 9 even when the quarter wave plate 7 causes a phase shift in the emitted light and becomes elliptically polarized light. .

  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 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 the phase correcting element 9 and projected onto the surface of the vibration plate 8, and the circular light in the reverse direction. Reflected as polarized light. The reflected light from the surface of the diaphragm 8 passes through the quarter-wave plate 7 and the phase correction element 9 again to be converted into P-polarized linearly polarized light, converged by the objective lens 4, and transmitted through the polarizing beam splitter 3. An image is formed on the optical axis x, 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, the vibration plate 8, and the phase correction element 9 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, the diaphragm 8, and the phase correction element 9, and the alignment operation between the objective lens 4 and the quarter-wave plate 7 is performed once. Just do it. 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 shows a second embodiment of the wave plate unit. Waveplate unit 51 of this example, phase correction element 9 _1, a pair of opposing transparent substrate 10 _1, 11 ₁ between the clamped and having twisted nematic liquid crystal in the liquid crystal layer 13 ₁ was sealed around a sealing 12 ₁ Is different from the wave plate unit 5 of the first embodiment. The liquid crystal layer 13 ₁ alignment film ₁₆ 1, 17 _1, transparent electrodes ₁₄ 1, 15 substantially to the substrate surface between the transparent substrate longitudinal direction of the liquid crystal molecules are opposed two when the voltage applied to the ₁ 0 They are parallel and are oriented in a state twisted at an angle of 90 ° + 180 ° × n (n = 0, 1, 2) continuously from one transparent substrate to the other transparent substrate.

The liquid crystal layer 13 ₁ rises in response to the voltage the liquid crystal molecules is applied to the transparent electrodes 14 _1, 15 _1, its tilt angle increases as away from the substrate surface of the transparent substrate. Accordingly, the tilt angle of the liquid crystal molecules is the largest in the intermediate region between the transparent substrates, and two liquid crystal layers having orientations that are effectively orthogonal to each other are symmetrically formed in the layer thickness direction from the intermediate region toward each substrate surface. Configured to have. As a result, the wavelength plate unit 5, by the phase correcting element 9 _1, passes through the quarter-wave plate 7 is reflected from the light and the reflector passes through the 1/4-wavelength plate 7 enters the diaphragm 8 Since both of the lights are equally phase-corrected, it is possible to convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light.

4A to 4F show wave plate units having various structures different from those of the first embodiment. Figure 4 waveplate unit 5 ₁ (A) is a combination of the diaphragm ₈₁ of the non-metal in the same quarter-wave plate 7 and the first embodiment and the phase correcting element 9. Diaphragm ₈₁ is made of a thin plate of glass or quartz or the like, the peripheral portion of the one side is formed thicker in a short rectangular tubular for reinforcement. One side of the quarter-wave plate 7 side of the diaphragm _81, the reflective surfaces 8 _1a is formed by subjecting a metal film. Diaphragm ₈₁ is rectangular tubular portion being integrally joined to the one surface of the opposite side of the quarter-wave plate 7 of the phase correcting element 9.

Figure 4 waveplate unit 5 ₂ (B) is a combination of the diaphragm ₈₂ of thin flat plates and the same quarter-wave plate 7 and the first embodiment and the phase correcting element 9. The diaphragm ₈₂ is a metal plate, is formed of a non-metallic plate such as a hard film or a glass plate. Diaphragm 8 _2, on one side opposite to the quarter-wave plate 7 of the phase correcting element 9, are joined together via a short rectangular tubular spacer 42 of metal or nonmetal. When the diaphragm ₈₂ is such as rigid film or glass plate, the reflecting surface is formed by subjecting a metal film on one side of the quarter-wave plate 7 side.

Figure 4 waveplate unit 5 ₃ (C) is a combination of a quarter-wave plate ₇₁ of the thin flat plate and the same vibrating plate 8 and the first embodiment and the phase correcting element 9. Quarter-wave plate ₇₁ is formed, for example, a film-like resin material plate. Quarter-wave plate ₇₁ is joined integrally with one surface of the opposite side of the diaphragm 8 of the phase correcting element 9.

Figure 4 waveplate unit _{5 4} (D) is in the same phase correction element 9 and the diaphragm _{8 1} of the first embodiment shown in FIG quarter-wave plate ₇₁ and the diagram (C) 4 (A) It is a combination. The quarter-wave plate ₇₁ and the vibrating plate ₈₁ are joined together respectively adjacent each side of the phase correcting element 9.

The wave plate unit 5 of the first embodiment and the wave plate units 5 _{1 to} 5 _{4 in} FIGS. 4A to 4D 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 41. By this glass plate 41, 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.

Figure 4 waveplate unit _{5 5} (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, a peripheral portion of one side is formed thicker in a short rectangular tubular for reinforcement. Rectangular tubular portion of the quarter-wave plate 7 ₂ are integrally bonded to one surface of the phase correcting element 9. Subjected to metal film 43 on one surface of opposite side of the quarter-wave plate 7 ₂ of the outer surface i.e. the rectangular tubular portion, the reflecting 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. 4 (F), similar to FIG. 4 (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. 4 (C), the subjected to metal film 43 on the outer surface thereof, the reflecting surface is formed. The inner surface peripheral edge portion of the quarter-wave plate 7 _3, short rectangular tubular reinforcing member 44 of metal or glass material are bonded together, the phase correcting element 9 is integrally bonded to the end face of該矩form tubular reinforcing member Has been. 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. Each waveplate unit of FIG. 4 (A) ~ (F) may replace the phase correcting element 9 and the phase correcting element 9 ₁ of FIG.

  FIG. 5 shows a third embodiment of the wave plate unit. The wave plate unit 52 of the present embodiment is different from the wave plate unit 5 of the first embodiment in that the quarter wave plate 71 is not a quartz plate but a liquid crystal element. The liquid crystal element has a liquid crystal layer 75 sandwiched between a pair of opposing transparent substrates 72 and 73 and sealed around with a seal 74. In the liquid crystal layer 75, liquid crystal molecules are arranged substantially in one direction in a plane parallel to the transparent substrate by alignment films 76 and 77 formed on the opposing surfaces of the transparent substrates 72 and 73, respectively. In the plane parallel to the transparent substrate and perpendicular to the transparent substrate, the layers are arranged so as to be inclined at a large pretilt angle at the center of the layer thickness substantially parallel to the transparent substrate and closer to the transparent substrate. By aligning the liquid crystal molecules in this way, in the quarter-wave plate 71, the incident angle dependence of the phase difference is reduced symmetrically with respect to the center position of the liquid crystal layer in the vertical direction of the transparent substrate. The quarter wavelength plate 71 can be used in place of the quarter wavelength plate 7 made of a quartz plate in the wavelength plate unit 5 of the second embodiment.

  FIG. 6A shows a fourth embodiment of the wave plate unit. The wave plate unit 53 of the present embodiment has a temperature sensor element 78 provided integrally with the quarter wave plate 7 in the wave plate unit 5 of the first embodiment shown in FIG. As shown in FIG. 6B, the temperature sensor element 78 includes a rectangular frame portion 79 and a tuning-fork type piezoelectric vibrating piece 80 disposed inside thereof. The tuning fork type piezoelectric vibrating piece 80 includes a base end portion 81 integrally coupled to the inner edge of the frame portion, and a pair of vibrating arm portions 82 extending in parallel from the base end portion. The temperature sensor element 78 is formed by externally processing the frame portion and the piezoelectric vibrating piece by wet etching or the like of a piezoelectric material such as quartz, and an excitation electrode is provided on the surface of the vibrating arm portion. Wiring for drawing out to the bottom is formed on the base end portion and the frame portion, respectively.

  In the temperature sensor element 78, the frame portion 79 is set to have a shape and dimensions corresponding to the inner dimensions of the rectangular cylindrical portion of the quarter-wave plate 7. On the inner side of the rectangular cylindrical portion of the quarter-wave plate 7, stepped portions 83 are integrally formed at each corner. The temperature sensor element 78 is fixed integrally with an adhesive or the like by placing the frame portion 79 on the step portion 83 in the rectangular cylindrical portion. The piezoelectric vibrating piece 80 is a region 84 in the quarter-wave plate 7 through which the laser light that passes through the quarter-wave plate 7 and reaches the reflecting surface 8a of the vibrating plate 8 and the reflected light from the reflecting surface passes. Designed not to enter.

  It is well known that a tuning fork type piezoelectric vibrating piece generally has a frequency temperature characteristic of a quadratic function or a cubic function. The tuning fork type piezoelectric vibrating piece 80 of the present embodiment selects a temperature range away from the inflection point of the quadratic function or the cubic function so that the operating temperature range of the optical sensor 1 is included in the range. As a result, the piezoelectric vibrating piece 80 has a frequency characteristic that changes almost linearly with respect to the temperature. Therefore, the temperature inside the quarter-wave plate 7 can be detected by measuring the frequency fluctuation. Based on this detected temperature, an applied voltage to the phase correction element 9 is determined and supplied from the AC power source 18 to the transparent electrodes 14 and 15. By arranging the temperature sensor element 78 in the vicinity of the quarter wavelength plate 7 in this way, the wavelength plate unit 53 more accurately corrects the phase shift of the emitted light generated in the quarter wavelength plate 7, and more It is possible to reliably convert linearly polarized light into circularly polarized light.

  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. 7 shows the positional relationship between the one-dimensional image sensor 61 formed of a CCD one-dimensional image sensor and the shape of the beam spot incident thereon, in contrast to the position of the two-dimensional image sensor 6. The one-dimensional image sensor 61 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 61a. Arrange so that it does not enter. Further, when the one-dimensional image sensor 61 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 61a.

  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 61a according to the position of the reflecting surface 8a of the diaphragm 8. The one-dimensional image sensor 61 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 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 61, 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. 8 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. As the wave plate unit 5, the wave plate unit shown in FIG. 2, FIG. 3, FIG. 4 (A) to (F), FIG. 5 or FIG.

  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 the phase correcting element 9 and projected onto the surface of the vibration plate 8, and the circular light in the reverse direction. Reflected as polarized light. The reflected light from the surface of the diaphragm 8 passes through the quarter-wave plate 7 and the phase correction element 9 again to be converted into P-polarized linearly polarized light, converted into parallel light by the objective lens 4, and transmitted through the polarizing beam splitter 3. Then, the light enters the two-dimensional image 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 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, the diaphragm 8 and the phase correction element 9 are integrated can significantly shorten the optical path length from the diaphragm 8 to the two-dimensional image sensor 6. At the time of assembly, alignment of the quarter-wave plate 7, the diaphragm 8, and the phase correction element 9 is not necessary, and alignment between the objective lens 4 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, 51, 52, 53 ... Wave plate unit, 6 ... Two-dimensional image sensor, 6a, 61a ... Light-receiving surface, 7 ... 1/4 wavelength plate, 8 ... vibration plate, 8a ... reflecting surface, 9 ... phase correction element, 10, 11, 72, 73 ... transparent substrate, 12, 74 ... seal, 13, 75 ... liquid crystal layer, 14, 15 ... Transparent electrode 16, 17, 76, 77 ... alignment film, 18 ... AC power supply, 19 ... drive circuit, 20 ... signal processing circuit, 22 ... collimating lens, 41 ... glass plate, 42 ... spacer, 43 ... metal film, 44 DESCRIPTION OF SYMBOLS Reinforcement member 61 ... One-dimensional image sensor 78 ... Temperature sensor element 79 ... Frame part 80 ... Tuning fork type piezoelectric vibrating piece 81 ... Base end part 82 ... Tuning fork vibrating arm part 83 ... Step part 84 ... region.

Claims (6)

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 objective lens from the polarizing beam splitter and transmitting the outgoing light, and a phase for adjusting the phase of the outgoing light passing through the quarter-wave plate Consisting of a correction element,
The optical sensor, wherein the quarter-wave plate, the phase correction element, and the diaphragm are integrated.   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 optical sensor according to claim 1, further comprising a temperature sensor for determining an adjustment amount of the phase of the emitted light by the phase correction element.   6. The optical sensor according to claim 5, wherein the temperature sensor is provided integrally with the quarter-wave plate.   6. The optical sensor according to claim 4, wherein the temperature sensor comprises a tuning fork type piezoelectric vibrator.

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