JP2014044161A - Optical displacement meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical displacement meter which attains cost reduction, speed-up of readout rate, and downsizing.SOLUTION: An optical displacement meter includes: a light source emitting light of two or more wavelengths; an imaging optical system in which light from the light source is incident on a sample through an optical fiber and an objective lens having chromatic aberration, and focused at an on-axis position different for each wavelength; separation means for spatially separating light reflected from a surface of the sample from a path of the imaging optical system by using an optical fiber coupler; a reflection light imaging optical system constituted of a detector having a plurality of detection parts on which the reflection light from the separation means is incident through a chromatic aberration lens and an astigmatism-generating optical element; and calculation means for calculating a distance on the basis of an output from the detector having the plurality of detection parts.

Description

  The present invention relates to an optical displacement meter, and more particularly to an optical displacement meter that is reduced in size, cost, and response speed.

FIG. 5 is a diagram showing a general configuration of a conventional optical displacement meter described in JP-A-10-9827.
In FIG. 5, light including a plurality of wavelength components emitted from a light source 1 such as an Xe lamp passes through a pinhole 6 a, is focused by an objective lens 4 through a beam splitter 3, and is irradiated onto a sample 5.

  The light reflected by the sample 5 is reflected by the beam splitter 3, passes through the pinhole 6 b, and enters the photodetector 7. The photodetector 7 includes a color filter 8 and a light receiving sensor 9. The color filter 8 uses a dichroic mirror for separating the three primary colors, and the light receiving sensor 9 includes three light receiving sensors 9R, 9G, and 9B for the three primary colors.

Here, in general, the focal length f of the lens is approximately,
(1 / f) = (n−1) × {(1 / r1) − (1 / r2)}
It is expressed. n is the refractive index of the glass material constituting the lens, and r1 and r2 are the curvature radii of the lens.

  As described above, the focal length f depends on the refractive index n of the lens, and the refractive index n of the lens depends on the wavelength λ of the light passing therethrough. Position.

  As shown in FIG. 5, if the light of wavelength λ2 is focused on the top of the sample 5, the light of the shorter wavelength λ1 is focused in front (upper) of the sample 5 because the focal length is shortened. Thus, the light with the long wavelength λ3 is focused behind the sample 5 (downward) because the focal length becomes long.

  For example, if the light of wavelength λ1 is B (blue), the light of wavelength λ2 is G (green), and the light of wavelength λ3 is R (red), the light of wavelength λ2 focused on the top of the sample 5 is the most. The light enters the light receiving sensor 9G through the color separation filter 8. The processing unit 10 detects that the amount of light received by the light receiving sensor 9G is the largest from the amounts of light received by the light receiving sensors 9B, 9G, and 9R, and determines the height of the sample 5 as the focus position of the green light.

FIG. 6 is a block diagram showing another conventional example, in which a line sensor is provided in the photodetector 7.
In FIG. 6, the light that has passed through the pinhole 6 a and entered the photodetector 7 becomes parallel light by the lens 11, is split into light of each wavelength component by the prism 12 as a spectral spectrometer, and is focused by the lens 13. Then, the light enters the line sensor 14 composed of a CCD (charge coupled device) or the like.

  In such a configuration, if the light reflected from the top of the sample 5 is green light having the wavelength λ 2 as described above, the most amount of light is irradiated to the position corresponding to the wavelength λ 2 on the line sensor 14. Therefore, if the relationship between the height position of the sample 5 and the light receiving position of the line sensor 14 is obtained in advance, the processing unit 10 can obtain the height of the sample 5 from the light receiving position of the line sensor 14.

  FIG. 7 shows another conventional example described in Japanese Patent Application Laid-Open No. 2011-39026. In the objective lens 4 having large chromatic aberration on the optical axis, the focal length varies depending on the light wavelength (color), blue light is close, and red The light is in the distance. The confocal point on the opposite side of the objective lens 4 with respect to the sample 5 to be measured is considered to be common regardless of the color, and if a white or broadband point light source is disposed here, the confocal point depends on the height of the sample 5 The color focused on the sample 5 changes one to one. Therefore, the principle that light of a color focused on the sample 5 can be extracted by providing a spatial filter such as a pinhole at the confocal position when the reflected light from the sample 5 returns is transmitted.

  Then, the spectroscope 26 such as a diffraction grating in the processing unit 10 is used to specify the color (light wavelength), thereby measuring the height (displacement) of the sample 5 having a 1: 1 relationship with the color. Yes.

  In general, the optical fiber 30 is used, white light (broadband light) is guided to the confocal point of the sensor head 15, the core of the optical fiber end surface 30 a is regarded as a pinhole, and the collimating lens 16 is diverged. Take the form you give.

  After the reflection at the sample 5, the light of the color focused on the sample 5 out of the white light irradiated on the sample 5 selectively gathers at the confocal position of the optical fiber end face 30a and is taken into the optical fiber core. Then, the light is guided to the spectroscope 26 via the optical fiber coupler 24. On the other hand, since the core of the optical fiber end surface 30a functions to limit the incident light equivalent to the pinhole, the light of other colors is blocked by the outer periphery of the core and enters the optical fiber 30. There is no.

  The spectroscope 26 detects the wavelength of the light returned into the optical fiber 30 and its output is input to the electronic circuit 28 for processing.

  FIG. 8 shows a collimating lens 50 with corrected chromatic aberration for making the light emitted from the optical fiber into parallel light, and the light to be measured which is collimated and propagated in one direction (Z direction) is orthogonal to the propagation direction Z. A polarizer 52 for almost equally dividing the linearly polarized light in two directions X and Y, and a zero-order wave plate 54 for transmitting two linearly polarized lights on the exit side of the polarizer 52 to make elliptically polarized light. A polarization separation element 56 disposed at an inclination in the 45 ° direction between XY to divide the elliptically polarized light on the exit side of the wave plate 54 into a polarization component in the 45 ° direction between XY and a polarization component in the 135 ° direction between XY; The calculation of (A−B) / (A + B) is performed using the light receiving elements 58A and 58B for detecting the light amounts of the respective polarization components and the light amount voltage signals A and B detected by the light receiving elements 58A and 58B. It consists of an analog arithmetic circuit 60 That.

JP-A-10-9827 JP 2011-39026 A

By the way, when the three paths using the dichroic mirror shown in FIG. 5 are relatively large, the dichroic mirror is expensive, the measurement range accuracy is limited, and the cost is high.
In addition, the prism and the array detector shown in FIG. 6 have a relatively large size, and there is a problem that the detection circuit is expensive and the reading rate cannot be increased.
Moreover, the thing using the polarizer and wavelength plate shown in FIG. 7 had the subject that the polarization separation element and the wavelength plate were expensive, and the efficiency fall by using a polarizer was caused.

  Accordingly, an object of the present invention is to provide an optical displacement meter that uses a chromatic aberration lens, an astigmatism element, and a detector having a plurality of detectors to reduce costs, increase the readout rate, and reduce the size. Yes.

The present invention has been made to solve the above problems, and in the optical displacement meter according to claim 1,
A light source including a plurality of wavelengths, and an imaging optical system that makes light from the light source enter the sample via an optical fiber and an objective lens having chromatic aberration, and focus at different on-axis positions for each wavelength;
Separation means for spatially separating reflected light from the sample surface from the path of the imaging optical system by an optical fiber coupler;
A reflected light imaging optical system comprising a detector having a plurality of detectors that enter the reflected light from the separating means via a chromatic aberration lens and an optical element that causes astigmatism;
An arithmetic means for calculating a distance based on an output from the detector having the plurality of detection units is provided.

In claim 2, in the optical displacement meter according to claim 1,
The optical fiber outlet is disposed so as to be at a confocal position with respect to the surface of the sample.

In claim 3, in the optical displacement meter,
A light source including a plurality of wavelengths, and an imaging optical system that injects light from the light source through a first pin pole and an objective lens having chromatic aberration, and focuses on a different axial position for each wavelength;
Separation means for spatially separating the reflected light from the sample surface from the path of the imaging optical system by a beam splitter; a second pinhole disposed at a position where the reflected light after separation is focused;
A reflected light imaging optical system comprising a detector having a plurality of detectors that enter the reflected light from the second pinhole via a chromatic aberration lens and an optical element that causes astigmatism;
An arithmetic means for calculating a distance based on an output from the detector having the plurality of detection units is provided.

In claim 4, in the optical displacement meter according to claim 3,
The first pinhole outlet is disposed so as to be at a confocal position with respect to the surface of the sample.

In Claim 5, in the optical displacement meter of Claim 1 or Claim 3,
The means for generating astigmatism is a cylindrical lens.

In Claim 6, in the optical displacement meter according to Claim 1 or Claim 3,
The means for generating astigmatism is a parallel plate glass arranged to be inclined on the optical axis.

As is apparent from the above description, according to the present invention, a light source including a plurality of wavelengths and light from the light source are incident on a sample via an optical fiber and an objective lens having chromatic aberration, and are on different axes for each wavelength. An imaging optical system for focusing at a position;
Separation means for spatially separating reflected light from the sample surface from the path of the imaging optical system by an optical fiber coupler;
A reflected light imaging optical system comprising a detector having a plurality of detectors that enter the reflected light from the separating means via a chromatic aberration lens and an optical element that causes astigmatism;
Since the calculation means for calculating the distance based on the output from the detector having the plurality of detection units is provided, the corresponding wavelength or distance can be calculated from the value calculated by the calculation means.

It is a principal part block diagram which shows an example of embodiment of the optical displacement meter of this invention. It is a figure which shows the state from which the reflected light has a different ellipticity on the surface of a detector. It is a principal part block diagram which shows other embodiment of the optical displacement meter of this invention. It is a principal part block diagram which shows other embodiment of the optical displacement meter of this invention. It is a figure which shows the structure of the conventional optical displacement meter. It is a figure which shows the structure of the conventional optical displacement meter. It is a figure which shows the structure of the conventional optical displacement meter. It is a figure which shows the principal part structure of the process part in FIG.

FIG. 1 is a block diagram showing an optical displacement meter of the present invention.
In the figure, a light source 1 is a white light source including a plurality of wavelengths. Light from the light source 1 enters the optical fiber 30a, exits from the exit port 30c, and is introduced into the imaging optical system 40. The imaging optical system 40 is provided with an objective lens (chromatic aberration lens) 4 and a sample 5 at the subsequent stage, and the light transmitted through the objective lens irradiates the sample 5.

  Here, from the sample, for example, light of wavelength λ1 (blue), light of wavelength λ2 (green), and light of wavelength λ3 (red) are generated as reflected light. The exit 30c of the optical fiber 30a can be regarded as a point light source, and is arranged so as to be in a confocal position with respect to the surface of the sample 5.

  The reflected light reflected by the sample 5 traces the same path as the incident path in the reverse direction and is spatially separated by the optical fiber coupler 24 formed in the optical fiber 30a, and the reflected light imaging optical system 41 via the optical fiber 30b. Is incident on. The reflected light emitted from the exit port 30d of the optical fiber 30b passes through the chromatic aberration lens 4a for setting the focal length to a different position for each wavelength, and further passes through the cylindrical lens (cylindrical lens) 43.

  The cylindrical lens 43 generates astigmatism in the reflected light, and generates an imaging shape depending on the wavelength on the surface of the quadrant photodiode 44. In the cylindrical lens 43, light included in a surface having a non-planar cross section is collected, but light included in a surface having a cross section is flat. As a result, when the light transmitted through the cylindrical lens 43 is viewed on a plane perpendicular to the optical axis, it generally has an elliptical intensity distribution.

  The cylindrical lens is used to cause astigmatism, and other elements may be used as long as they have the same function. Any optical system that is not subject to rotation with respect to the optical axis may be used, and as an example, astigmatism can be generated even when a parallel plate glass that is inclined with respect to the optical axis is used.

  2 shows that the reflected light emitted from the exit port 30d of the optical fiber 30b shown in FIG. 1 is transmitted through the chromatic aberration lens 12a and through the cylindrical lens (cylindrical lens) 43, and has different ellipticities on the surface of the quadrant photodiode 44. It shows the state.

  Outputs from the four-divided photodiodes 44 are respectively input to the calculating means 42, and the output of each element is calculated to obtain information on the image shape on the detection surface. For example, if the calculation of ((A + B)-(C + D)) / (A + B + C + D) is performed from the outputs of the elements A, B, C, and D in FIG. It becomes. Since the wavelength can be specified from such a calculation result, the height can be finally obtained. Note that an electric circuit, a personal computer, a microcontroller, or the like may be used as the calculation means.

  The detection element is not limited to the four-divided photodiode, and the intensity ratio of the plurality of detection units may be changed by changing the imaging shape. For example, a two-divided photodiode may be used.

3 and 4 show other embodiments. In these examples, a point using a pinhole instead of an optical fiber, a point where the reflected light is separated using a beam splitter, and the separated reflected light are shown. The difference is that the light is incident on the imaging optical system via a pinhole.
In FIG. 3, the light from the light source 1 is introduced into the imaging optical system 40 through the first pinhole 6a. In FIG. 4, the first pinhole 6a is provided directly in the imaging optical system 40. These pinholes are arranged so as to be confocal with respect to the sample surface.

  Further, as means for spatially separating the reflected light, the beam splitter 3 is disposed between the pinhole 6a and the sample surface, and the second pinhole is located at a position where the reflected light separated by the beam splitter 3 is focused. 6b is arranged. Since the configuration and function of the reflected light imaging optical system thereafter are the same as those shown in FIG. 1, the description thereof is omitted here.

2 and 3 also functions in the same manner as the optical displacement meter shown in FIG.
According to the above-described configuration, the optical elements and photoelectric conversion elements that make up the chromatic aberration and astigmatism constituting the reflected light imaging optical system can be used at low cost, so that they are configured at a lower cost than commercially available spectrometers. Can do.

In addition, the quadrant photodiode can operate at a low cost and at a high speed as compared with hundreds to thousands of element arrays used in a spectrometer.
Furthermore, since the optical system is simple, the optical system is small and light, and can be applied as a sensor for incorporation.

The optical displacement meter of the present invention can accurately measure the height of a sheet-like or thin plate-like measurement object by measuring the surface and the sensor while moving relative to each other.
Moreover, the thickness of a measuring object is computable by arrange | positioning and measuring each of a sheet-like or thin-plate-like measuring object on both sides of a measuring object with a pair of sensors.
In addition, when there is a possibility that the sensors arranged on both sides may be relatively displaced in the optical axis direction of the light source light imaging optical system, the thickness of the object to be measured can be set correctly by providing a means for measuring the distance between the sensors. Can be calculated

The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. For example, a collimating section may be provided by arranging a collimating lens in the middle of the incident light path or the reflected light path.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

1 Light source 3 Beam splitter 4 Objective lens (chromatic aberration lens)
DESCRIPTION OF SYMBOLS 5 Sample 6 Pinhole 7 Photodetector 8 Color filter 9 Light receiving sensor 10 Processing part 11, 13 Lens 12 Prism 14 Line sensor 15 Sensor head 16 Collimator lens 24 Optical fiber coupler 28 Electronic circuit 30 Optical fiber 30a, 30d Output port 40 Connection Image optical system 41 Reflected light imaging optical system 42 Arithmetic means 43 Cylindrical lens 44 Quadrant photodiode 50 Collimate lens 52 Polarizer 54 Wavelength plate 56 Polarization separation element 58 Light receiving element 60 Analog arithmetic circuit

Claims (6)

A light source including a plurality of wavelengths, and an imaging optical system that makes light from the light source enter the sample via an optical fiber and an objective lens having chromatic aberration, and focus at different on-axis positions for each wavelength;
Separation means for spatially separating reflected light from the sample surface from the path of the imaging optical system by an optical fiber coupler;
A reflected light imaging optical system comprising a detector having a plurality of detectors that enter the reflected light from the separating means via a chromatic aberration lens and an optical element that causes astigmatism;
An optical displacement meter comprising a calculation means for calculating a distance based on outputs from a detector having the plurality of detection units.   2. The optical displacement meter according to claim 1, wherein the optical fiber outlet is disposed so as to be in a confocal position with respect to the surface of the sample. A light source including a plurality of wavelengths, and an imaging optical system that injects light from the light source through a first pin pole and an objective lens having chromatic aberration, and focuses on a different axial position for each wavelength;
Separation means for spatially separating the reflected light from the sample surface from the path of the imaging optical system by a beam splitter; a second pinhole disposed at a position where the reflected light after separation is focused;
A reflected light imaging optical system comprising a detector having a plurality of detectors that enter the reflected light from the second pinhole via a chromatic aberration lens and an optical element that causes astigmatism;
An optical displacement meter comprising a calculation means for calculating a distance based on outputs from a detector having the plurality of detection units.   4. The optical displacement meter according to claim 3, wherein the first pinhole outlet is disposed so as to be in a confocal position with respect to the surface of the sample.   The optical displacement meter according to claim 1 or 3, wherein the means for generating astigmatism is a cylindrical lens.   The optical displacement meter according to claim 1 or 3, wherein the means for generating astigmatism is a parallel plate glass arranged to be inclined on the optical axis.