JPH04363648A - Optical member evaluation device - Google Patents

Abstract

PURPOSE:To obtain an optical member evaluation device which can clearly detect a defect of an optical member, independently find out the defect on each cross section of the optical member with comparatively simple constitution and adjustment. CONSTITUTION:The optical member evaluation device which is able to obtain the information of a cross section image without any noise caused by diffraction and the like and enables exact evaluation of an optical member 10 by image- forming the cross section image at a specific position of the inside of the optical member 10 in the outside thereof and photographing the image with the use of a photographing means 22 in an image relay optical system 21 is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member evaluation apparatus for detecting defects such as impurities, growth stripes, striae, etc. inherent in optical members such as crystals and glasses and evaluating the optical members.

0002

[Prior Art] If defects such as impurities, growth stripes, or striae are present in various optical members used in the field of optoelectronics, they will not be able to exhibit the desired performance. In some cases, it is necessary to evaluate the optical member by detecting the presence or absence of these defects.

[0003] As an optical member evaluation method for evaluating these optical members, a shadow graph (shad
ow graph method, and Schlieren (shlie) method.
ren) etc. are known.

FIG. 5 is a diagram showing the configuration of a conventional optical member evaluation apparatus using the shadow graph method.

As shown in FIG. 5, a beam expander 12 converts a laser beam emitted from a laser device 11 into a parallel beam R whose beam diameter is expanded, and an optical member 10
After passing through, it is projected onto the screen 13. The image formed on the screen 13 is photographed and observed using a CCD camera 14 or the like for evaluation.

That is, if the optical member 10 has no defects,
Since the laser beam R that has passed through the optical member 10 reaches the screen 13 as parallel light, no image is formed on the screen 13, but the optical member 10 has defects such as impurities, growth stripes, or striae. Since the density distribution in that part is different from that in other parts, a difference in refractive index occurs, and as a result, an image of interference fringes corresponding to the defect is formed on the screen 13. Therefore, by observing the presence or absence of these interference fringes, it is possible to detect the presence or absence of defects and to evaluate the optical member.

FIG. 6 is a diagram showing the configuration of a conventional optical member evaluation apparatus using the Schlieren method. As shown in FIG. 6, this device has the same configuration as described above until the laser beam emitted from the laser device 11 is converted into parallel light R whose beam diameter is expanded by the beam expander 12 and passed through the optical member 10. This is the same as the shadow graph method, but the light that has passed through the optical member 10 is focused by a condensing lens 15, and a knife edge 16 is placed at the focal point P of this condensing lens 15, so that the light passing through the lower half of the focal point P is focused. This method differs from the shadow graph method described above in that the light is projected onto the screen 13 after being blocked.

That is, if there is no defect in the optical member 10, the parallel light R will be completely focused on the focal point P by the condenser lens 15 without disturbing the parallelism, so that no image will appear on the screen 13. Not formed. On the other hand, if there is a defect in the optical member 10, when the parallel light R passes through the optical member 10, the parallelism is disturbed due to the defect, and therefore,
The light beam that has passed through the defect passes through the condensing lens 15 and then passes through a place other than the focal point P, and a part of it is blocked by the knife edge 16. As a result, a bright and dark image corresponding to the defect is formed on the screen 13. The image formed on the screen 13 is photographed and observed using a CCD camera 14 or the like for evaluation.

[0009]

[Problems to be Solved by the Invention] However, in all of the above-mentioned conventional methods, many diffraction patterns of the laser beam from the outer periphery of the optical member occur, and this diffraction pattern becomes noise and causes damage to the optical member. The disadvantage is that internal defects make it difficult to distinguish patterns, making accurate evaluation difficult. In addition, the Schlieren method has a knife edge 1 at the focal point P.
There is also a drawback that adjustment for accurately arranging 6 is complicated. In addition, in both methods, the information obtained by integrating all the information due to defects in each part along the optical path length of the optical member is only displayed as a bright and dark image on the screen, so defects in the cross section of each part can be detected independently. There is a drawback that it cannot be evaluated.

The present invention has been made against the above-mentioned background, and is capable of clearly detecting defects in an optical member, independently detecting defects in each cross section of the optical member, and having a relatively simple structure. The object of the present invention is to provide an optical member evaluation device that is simple and easy to adjust.

[0011]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides (1) a light source that generates light that passes through an optical member; and a light source that generates light that is emitted from the light source and passes through the optical member. an image relay optical system that forms a cross-sectional image of a specific position inside the optical member on the outside of the optical member; and an image relay optical system arranged at an imaging point of the cross-sectional image of the specific position of the optical member formed by the image relay optical system. The configuration includes an image pickup means.

Further, as an aspect of configuration 1, (2) in the optical member evaluation apparatus of configuration I, a moving means for changing the relative positions of the optical member and the imaging means with respect to the image relay optical system is provided. It has a characteristic configuration.

Furthermore, as an aspect of configuration 2, (3)
In the optical member evaluation device according to configuration 2, the imaging means converts a captured image into a predetermined image signal and sends it out, and also inputs the image signal of the optical member sent out from the imaging means. The present invention is characterized in that it includes an information processing means for converting into evaluable information.

[0014] Further, as an aspect of any one of configurations 1 to 3, (4) the optical member evaluation apparatus according to any of configurations 1 to 3 is characterized in that a vibration device for causing micro vibrations to the optical member is provided. The structure is as follows.

Furthermore, as aspects of configurations 1 to 4, (
5) In the optical member evaluation apparatus according to any one of configurations 1 to 4, when the light emitted from the light source is coherent light, a coherence reduction means for weakening the coherence is provided. It has a characteristic configuration.

[0016] As aspects of configurations 1 to 5, (
6) In the optical member evaluation apparatus according to any one of configurations 1 to 5, the optical member is housed in a container having a light passage window, and matching oil having a refractive index substantially the same as that of the optical member is contained in the container. The structure is characterized in that it satisfies the following.

[0017]

[Operation] According to the above configuration 1, since the cross-sectional image of the optical member formed on the imaging means is formed by the image relay optical system, there is no noise in the diffraction image.
Defects in optical members can be accurately evaluated.

Further, according to configuration 2, since it is possible to form a cross-sectional image of a desired position of the optical member on the imaging means, it is possible to evaluate each cross-section of the optical member.

According to configuration 3, the information processing means
For example, it becomes possible to obtain a three-dimensional image by combining the image signals of each cross-sectional image of the optical member, making it possible to perform more appropriate evaluation.

Furthermore, according to configuration 4, by micro-vibrating the optical member, defects inside the optical member, such as impurities or crystal growth stripes, have an extremely small difference in refractive index with other parts. In this case, it is possible to form a clear image of the boundary with other parts due to the principle of so-called Schurring interference.

Further, according to configuration 5, when a laser beam having extremely excellent wavelength unity and straightness is used as the light to pass through the optical member, the coherent property of the laser beam allows the optical member to pass through the optical member. Although interference noise may occur due to surface reflection, this noise can be removed by reducing the coherence using the coherence reducing means.

Furthermore, according to configuration 6, by storing the optical member to be measured in a container and filling the container with matching oil, the optical member to be measured can be of any shape that has not been subjected to pretreatment such as optical polishing. The device can be used as is, which greatly simplifies measurement work.

[0023]

【Example】

First Embodiment FIG. 1 is a diagram showing the configuration of an optical member evaluation apparatus according to a first embodiment of the present invention. Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIG.

In FIG. 1, numeral 10 is an optical member, numeral 11 is a laser device, numeral 12 is a beam expander, numeral 21 is an image relay optical system, numeral 22 is a CCD camera, numeral 24 is a movable stage, and numeral 25 is a fixed stage, reference numeral 26 is a controller, reference numeral 28 is a computer,
The laser device 11, whose reference numeral 29 is a display and 30 is a base, is a He-Ne laser device that emits laser light with an output of about 1 mW, a wavelength of 632.8 nm, and a beam diameter of 1 mmφ.

The beam expander 12 includes a concave lens 12
a and a convex lens 12b, the beam diameter of the laser beam emitted from the laser device 11 with a beam diameter of 1 mm is expanded to about 5 times that of 5 mm, and converted into a laser beam R that is parallel light.

The optical member 10 is an object to be evaluated, and in this example, the cross section is 3×3 mm and the length in the optical axis direction is 5 mm.
It is a NYAB crystal with a diameter of mm. The optical member 10 is fixedly held at the upper end of a pedestal 24a fixed to a movable stage 24 via a support member 24b.
The beam expander 12 and the beam expander 12 are arranged with the same optical axis.

The image relay optical system 21 is composed of two convex lenses 21a and 21b arranged to share an optical axis with the laser device 11 and beam expander 12. This image relay optical system 21 forms a cross-sectional image of the optical member 10 at a distance d1 from the front (left side in the figure) surface of the convex lens 20 at a position at a distance d2 from the rear (right side in the figure) surface of the convex lens 21. It is something that makes you In this case, the imaging condition is expressed by the following equation.

[0028]d2 =M×L−M2×d1...(
1) However, M=f2 /f1 L=f2 +f1 f1 ; Focal length of convex lens 20 f2 ; Focal length of convex lens 21.

The CCD camera 22 includes the above-mentioned convex lens 21.
The image formed by the image relay optical system 21 consisting of a and 21b is converted into an image signal and sent to the computer 28.
It is sent to This CCD camera 28 is of a type using silicon crystal, and is fixed to the fixed stage 25. In addition, in this example, the light receiving surface is 12×
A size of about 12 mm is used.

The computer 28 constitutes the information processing means of the present invention, and the computer 28 composes the information processing means of the present invention.
The image signal sent from the CD camera 22 is subjected to predetermined image processing, such as processing to synthesize a stereoscopic image from a plurality of cross-sectional images, and other image analysis processing, and then displayed on the display 28.
At the same time, the movable stage 24 is moved by controlling the controller 26 so that the optical member 10 and the CCD camera 22 are set to positions that satisfy the above equation (1). The image of the desired cross section is C
This is to control so that the image is formed on the imaging surface of the CD camera 22. In this case, the optical member 10 may be made to stand still at each position that satisfies the above formula (1) and a cross-sectional image at each position may be displayed on the display 29, or the optical member 10 may be moved at a predetermined speed. A stereoscopic image may be synthesized by sequentially inputting image signals sent from the CCD camera 22 while moving the camera 22 continuously, and performing image processing.

The movable stage 24 can be moved on a rail (not shown) installed on the base 30 parallel to the common optical axis of the laser device 11, beam expander 12, convex lens 20, and convex lens 21. A motor and other movement mechanisms are provided inside, and the movement of each can be controlled by the controller 26.

According to the apparatus configured as described above, the optical member 10
Since the cross-sectional image of the image is focused on the imaging means by the image relay optical system 21 consisting of two convex lenses 21a and 21b for observation and analysis, there is extremely little noise due to diffraction, etc., so it is possible to clearly identify patterns caused by defects. can be identified. In addition, since defects in each cross section of the optical member 10 can be detected independently, by applying appropriate image processing to the image of each cross section, it is also possible to synthesize and evaluate a three-dimensional image of the defect, which allows for more appropriate evaluation. Evaluation becomes possible. Furthermore, since the structure is relatively simple and adjustment is relatively easy, there is also the advantage that manufacturing adjustment is easy.

Second Embodiment FIG. 2 is a diagram showing the main structure of a second embodiment of the present invention. In this embodiment, a vibration device 201 is installed at the upper end of the pedestal 24a of the movable stage 24 in the first embodiment shown in FIG.
is provided to apply minute vibrations to the optical member 10, thereby improving the contrast of the defect image obtained by the CCD camera 22.The other configuration is the same as the first embodiment. . Therefore, in the following, points unique to this embodiment will be mainly explained, and parts common to the first embodiment will be denoted by the same reference numerals, and detailed explanation thereof will be omitted.

The vibration device 201 is composed of a piezo element, etc., and is driven and controlled by a controller 202, which is controlled by a computer 28. This vibration device 201 has an amplitude of about several tens of μm at maximum and a frequency of 100 μm, which is higher than the field frequency of the television monitor 29, in the optical axis direction of the image relay optical system 21, in a direction orthogonal to the optical axis direction, or in any direction. It is possible to apply minute vibrations of approximately several hundred Hz to the optical member 10 via the support member 24b.

In this embodiment, a NYAB crystal is used as the optical member 10, and the vibration device 201 generates vibrations with a maximum amplitude of ±20 μm (1 to 10 μm) and a frequency of 100 Hz.
By performing measurements while applying minute vibrations, we were able to obtain extremely clear images of impurities inherent in the crystal and crystal growth fringes. Note that impurities and crystal growth stripes inherent in the crystal have a refractive index difference of 10-5 to 10-1 compared to other normal parts.
6, which is extremely small, so it was difficult to obtain a clear image even with the apparatus of the first embodiment.

Third Embodiment FIG. 3 is a diagram showing the main structure of a third embodiment of the present invention. This embodiment uses two convex lens systems 1 instead of the beam expander 12 in the first embodiment shown in FIG.
Using a Newtonian beam expander 102 consisting of 02a and 102b, the focal point O of the convex lens system 102a is
A rotating disc-shaped ground glass 301 is placed near the ground glass 301, and the laser beam emitted from the laser device 11 hits this ground glass 3.
01 to weaken the coherence of the laser beam emitted from the beam expander 12. This makes it possible to prevent the generation of noise due to an interference phenomenon caused by a portion of the laser beam R being reflected by an optical component such as an ND filter placed in front of the CCD camera.

The ground glass 301 constitutes the coherence reduction means of the present invention, and is made of optical glass such as BK-7 and formed into a disk shape with a thickness of 1 mm and a diameter of 50 mm, and the surface is polished with #500. It has been polished to look like pickled glass. Further, this pick-pocket glass 301 can be rotated by a motor 302 at a rotational speed of about 100 rpm with the center of the disk as the center of rotation, and point O is located on the outer periphery. That is, the position of the ground glass at point O is always changed, and the laser beam passing through the ground glass 301 at point O is made to have coherence weakened by the unevenness of the surface of the ground glass that changes randomly. . In addition, as a means for reducing coherence,
Instead of the pick-pocket glass 301, a material having a similar effect, such as a transparent material in which an emulsion is dispersed, may be used.

According to this example, an image completely free of interference noise could be obtained even when an ND filter was placed in front of the CCD camera.

Fourth Embodiment FIG. 4 is a diagram showing the main structure of a second embodiment of the present invention. In this embodiment, it is possible to directly measure an optical member 10 of any shape that has not been subjected to pretreatment such as optical polishing, and the optical member 10 is placed in a container 100 that is formed so that light can pass therethrough. 10 and filled with matching oil 101, the container 100 is placed on a movable stage 24 so that the optical member 10 is placed in the same position as the optical member 10 in the first embodiment shown in FIG.
It was designed to be kept at .

In FIG. 4, the container 100 has a substantially rectangular parallelepiped outer shape and a hollow box inside, and has a pair of parallel light inputs disposed perpendicularly to the traveling direction of the laser beam R. - The exit windows 102 and 103 are made of optical glass such as BK-7 or fused silica, and the other side walls are made of metal,
It is made of plastic etc. Both sides of the light input/output windows 102 and 103 are sufficiently optically polished.

[0041] The optical member 10 is not pretreated.
It is a YAB crystal. Here, pretreatment refers to the optical member 10
Before measuring, the optical member 10 is optically polished so that its light input and output surfaces are parallel to each other and the shape is adjusted to a predetermined level of smoothness. Normally, if this pretreatment is not performed, the unevenness of the light entrance and exit surfaces will cause reflection and refraction that are harmful to measurements, making it difficult to obtain images of defects inside the crystal.

The matching oil 101 is applied to the optical member 10.
It is made of a substance that has a refractive index that is approximately the same as that of . When the optical member 10 is NYAB crystal, the wavelength is 1.062μ
For light of m, the ordinary ray refractive index n0 is 1.7553, the extraordinary ray refractive index ne is 1.6869, and the average refractive index n is about 1.70. This refractive index matching oil 101 can be obtained by mixing 1-chloronaphthalene and joodomethane at an appropriate mixing ratio.

By accommodating the optical member 10 in the container 100 and filling it with matching oil 101, the matching oil 101 penetrates into the uneven portions of the optical member 10 and acts to fill them, so that the inside of the container 100 is almost completely empty. This is approximately equivalent to a state filled with a substance having a uniform refractive index. Therefore, it is possible to obtain a defect image inside the optical member 10 without pre-processing the optical member 10.

[0044] In each of the above embodiments, a laser device is used as a light source that generates light that passes through an optical member, but this does not necessarily have to be a laser device. Any available wavelength may be used, but it is necessary to use one with an appropriate wavelength depending on the type of optical member to be evaluated. For example, if the optical member is YIG (Y3 F
e5 O12) If it is a crystal, the wavelength is 1.15 μm.
A He-Ne laser device with a wavelength of 1.5 μm or a semiconductor laser device with a wavelength of 1.5 μm is used. In that case, the imaging means used is one sensitive to these wavelengths, such as Ge
Of course, a CCD camera or the like using a crystal can be used.

Furthermore, in each of the above embodiments, a CCD camera is used as an imaging means, and the image signal sent from the CCD camera is processed by a computer and displayed on a display. Other imaging means may also be used. Furthermore, it is not necessary to use a computer as the information processing means, and the image sent from the imaging means may be directly displayed on a display.

[0046]

As described in detail above, the present invention is capable of forming a cross-sectional image of a specific position inside an optical member on the outside of the optical member using an image relay optical system, and capturing this image using an imaging means. This makes it possible to obtain cross-sectional image information free of noise caused by diffraction and the like, thereby providing an optical member evaluation device that enables more accurate evaluation of optical members.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an optical member evaluation apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a main part configuration of an optical member evaluation apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing the main part configuration of an optical member evaluation apparatus according to a third embodiment of the present invention.

FIG. 4 is a diagram showing the main part configuration of an optical member evaluation apparatus according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of an apparatus using a conventional shadow mask method.

FIG. 6 is a diagram showing the configuration of an apparatus using the conventional Schlieren method.

[Explanation of symbols] 10... Optical member, 11... Laser device, 12... Beam expander, 21... Image relay optical system, 22... CCD
Camera, 24, 25...Movable stage, 26, 27...Controller, 28...Computer constituting information processing means, 29...Display, 30...Base, 201...Vibration device, 301...Spotted glass, 100...Container, 101... matching oil.

Claims (6)

[Claims] 1. A light source that generates light that passes through an optical member, and a cross-sectional image of a specific position inside the optical member formed by the light emitted from the light source and passed through the optical member, which is imaged on the outside of the optical member. An optical member evaluation device comprising: an image relay optical system that performs an image relay optical system; and an imaging means disposed at an imaging point of a cross-sectional image of a specific position of the optical member formed by the image relay optical system. 2. The optical member evaluation apparatus according to claim 1, further comprising a moving means for changing the relative positions of the optical member and the imaging means with respect to the image relay optical system. Device. 3. The optical member evaluation apparatus according to claim 2, wherein the imaging means converts the taken image into a predetermined image signal and sends out the image signal, and the imaging means converts the taken image into a predetermined image signal and sends out the image. An optical member evaluation device comprising an information processing means for inputting an image signal of an optical member and converting it into information that can be evaluated. 4. The optical member evaluation apparatus according to claim 1, further comprising a vibration device that causes minute vibrations of the optical member. 5. The optical member evaluation device according to claim 1, wherein when the light emitted from the light source is coherent light, coherence reduction that weakens the coherence. An optical member evaluation device characterized by comprising means. 6. The optical member evaluation apparatus according to claim 1, wherein the optical member is housed in a container having a light passage window, and a refractive index substantially the same as that of the optical member is placed in the container. An optical member evaluation device characterized in that it is filled with matching oil having a refractive index.