JP3053133B2 - Optical member evaluation device - Google Patents

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 or striae present in an optical member such as a crystal or glass and evaluating the optical member.

[0002]

2. Description of the Related Art When various optical members used in the field of optoelectronics or the like contain defects such as impurities, growth stripes or striae, predetermined performance cannot be exerted. In this case, it is necessary to detect the presence or absence of these defects and evaluate the optical member.

[0003] As an optical member evaluation method for evaluating these optical members, a shadow graph (shad) has conventionally been used.
ow graph method, schlieren (shlier)
en) etc. are known.

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

[0005] As shown in FIG. 5, a laser beam emitted from a laser device 11 is converted into a parallel beam R whose beam diameter is expanded by a beam expander 12,
, And is projected on the screen 13. The image formed on the screen 13 is evaluated by photographing with a CCD camera 14 and observing the image.

That is, if the optical member 10 has no defect,
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. Then, since the density distribution of the portion is different from that of other portions, 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 the interference fringes, the presence or absence of a defect can be detected, and the evaluation of the optical member can be performed.

FIG. 6 is a diagram showing the configuration of a conventional optical member evaluation apparatus based on the Schlieren method. As shown in FIG. 6, this device is configured as described above until the laser beam emitted from the laser device 11 is converted into a parallel beam R whose beam diameter is expanded by the beam expander 12 and passes through the optical member 10. Same as the shadow graph method, except that the light passing through the optical member 10 is focused by a condenser lens 15, and a knife edge 16 is arranged at the focal point P of the condenser lens 15 and passes through the lower half of the focal point P. This is different from the shadow graph method in that the light is projected onto the screen 13 after being blocked.

That is, when the optical member 10 has no defect, the parallel light R is completely focused on the focal point P by the condenser lens 15 without disturbing the parallelism. Not formed. On the other hand, if the optical member 10 has a defect, the parallelism is disturbed by the defect when the parallel light R passes through the optical member 10, and therefore,
After passing through the defect, the light beam passes through the condenser lens 15, passes through a portion other than the focal point P, and a part of the light beam 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 evaluated by photographing with a CCD camera 14 and observing the image.

[0009]

However, in each of the above-mentioned conventional methods, many diffraction patterns of the laser beam from the outer peripheral portion of the optical member are generated, and this diffraction pattern becomes noise and the optical member becomes undesired. There is a disadvantage that it is difficult to determine a pattern due to an internal defect, and it is difficult to perform accurate evaluation. The Schlieren method uses 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 either method, since the information in the form of integrating all the information due to the defect of each part along the optical path length of the optical member is simply expressed as a bright and dark image on the screen, the defect of the cross section of each part is independently determined. There is a disadvantage that cannot be evaluated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and it is possible to clearly detect a defect in an optical member, to detect a defect in each section of the optical member independently, and to have a relatively simple structure. It is an object of the present invention to provide an optical member evaluation device that is simple and easy to adjust.

[0011]

In order to solve the above-mentioned problems, the present invention provides: (1) a light source for generating light to pass through an optical member, and light emitted from the light source and passing through the optical member. a image relay optical system that forms a cross-sectional image of a particular location within the optical member to the optical member outside being, at a distance d ₁ a rearward position of the specific position with respect to the particular position the first convex lens arranged focal length f _1, and the position of the rear image of the specific position of the second a convex lens wherein the optical member of the focal distance f ₂ in combination with the convex lens of the first a second convex lens for focusing at a distance _{d 2} relative to the second lens comprising _{a, d 2 = (f 2 /} f 1) (f 1 + f 2) - (f 2 / f
₁ ) an image relay optical system having a relation of ² · d ₁ ,
And an imaging unit arranged at an image forming point of a cross-sectional image at a specific position of the optical member formed by the image relay optical system.

Further, as an aspect of Configuration 1, (2) In the optical member evaluation apparatus of Configuration I, a moving means for changing a relative position of the optical member and the image pickup means with respect to the image relay optical system is provided. The configuration was characterized.

Further, according to a second aspect of the present invention, there is provided (3) in the optical member evaluation apparatus of the second aspect, wherein the image pickup means converts the picked-up image into a predetermined image signal and sends it out. An information processing means for inputting an image signal of the optical member sent from the means and converting the image signal into evaluable information is provided.

Further, as one aspect of any one of the constitutions 1 to 3, (4) in the optical member evaluation device of any one of the constitutions 1 to 3, a vibration device for minutely vibrating the optical member is provided. The configuration was adopted.

Further, as an aspect of the constitutions 1 to 4,
(5) In the optical member evaluation device according to any one of the constitutions 1 to 4, when the light emitted from the light source is coherent light, a coherence reducing means for weakening the coherence is provided. .

Then, as an embodiment of the constitutions 1 to 5,
(6) In the optical member evaluation device according to any one of the constitutions 1 to 5, the optical member is housed in a container having a light passage window, and a matching having a refractive index substantially equal to the refractive index of the optical member in the container. It is configured to be filled with oil.

[0017]

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.
The defect of the optical member can be accurately evaluated.

Further, according to the configuration 2, it is possible to form a cross-sectional image of a desired position of the optical member on the image pickup means, so that each cross section of the optical member can be evaluated.

According to the configuration 3, the information processing means
For example, it is also possible to obtain a three-dimensional image by synthesizing the image signals of the respective cross-sectional images of the optical member, thereby enabling more appropriate evaluation.

Further, according to the fourth aspect, by causing the optical member to vibrate minutely, the defect inside the optical member has a very small difference in refractive index from other parts, such as impurities or crystal growth stripes. Also in this case, it is possible to form a clear image of the boundary with other parts by the principle of so-called interference of interference.

According to the fifth aspect, when a laser beam having extremely excellent wavelength uniformity and linearity is used as the light passing through the optical member, the coherent property of the laser beam causes the optical component to have an optical component. In some cases, interference noise due to the surface reflection of the light may occur, but this noise can be removed by reducing the coherence by the coherence reducing means.

Further, according to the sixth aspect, the optical member to be measured is housed in a container and filled with a matching oil, so that the optical member to be measured has an arbitrary shape that has not been subjected to a pretreatment such as optical polishing. It can be used as it is, and the measuring operation can be remarkably facilitated.

[0023]

EXAMPLES First Embodiment FIG. 1 is a diagram showing a 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, reference numeral 10 denotes an optical member, reference numeral 11 denotes a laser device, reference numeral 12 denotes a beam expander, reference numeral 21 denotes an image relay optical system, reference numeral 22 denotes a CCD camera, reference numeral 24 denotes a movable stage, and reference numeral 25 denotes a fixed stage. Stage, reference numeral 26 denotes a controller, reference numeral 28 denotes a computer, reference numeral 29 denotes a display, reference numeral 30 denotes a base, the laser device 11 has an output of about 1 mW, a wavelength of 632.8 nm,
This is a He—Ne laser device that emits a laser beam having 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 and having a diameter of 1 mmφ is enlarged to about 5 times 5 mmφ, and converted into a laser beam R as parallel light.

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

The image relay optical system 21 is composed of two convex lenses 21a and 21b which have the same optical axis as the laser device 11 and the beam expander 12. This image relay optical system 21 is a convex lens
21a front of those for imaging in a position where they cross-sectional images of the optical member 10 from (in the drawing the left) surface at a distance d ₁ from the rear (the right in the drawing) surface of the convex Reference Bu 21b at a distance d _2. In this case, the imaging condition is represented by the following equation. d ₂ = M × LM−M ² × d ₁ (1) where M = f ₂ / f ₁ L = f ₂ + f ₁ f ₁ ; focal length of convex lens ゛21 a f ₂ ; focal length of convex lens ゛21 b

D ₂ = M × LM−M ² × d ₁ (1) where M = f ₂ / f ₁ L = f ₂ + f ₁ f ₁ ; focal length of convex lens 20 f ₂ ; focal length of convex lens 21 It is.

The CCD camera 22 includes the above-described convex lens 21.
a) converts the image formed by the image relay optical system 21 into image signals,
To be sent. The CCD camera 28 is of a type using a silicon crystal, and is fixed to the fixed stage 25. In this embodiment, the light receiving surface is 12 ×
The one having a size of about 12 mm is used.

The computer 28 constitutes the information processing means of the present invention.
A predetermined image processing is performed on the image signal sent from the CD camera 22, for example, a processing of synthesizing a stereoscopic image from a plurality of cross-sectional images, and other image analysis processing are performed, and the display 28 is processed.
And the controller 26 is controlled to move the movable stage 24 so that the optical member 10 and the CCD camera 22 are set at the positions satisfying the above-described equation (1). The image of the desired section is C
The control is performed so that an image is formed on the imaging surface of the CD camera 22. In this case, the optical member 10 may be stopped at each position that satisfies the above expression (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. Alternatively, a stereoscopic image may be synthesized by successively inputting image signals sent from the CCD camera 22 and performing image processing while moving continuously.

The movable stage 24 can be moved on a base 30 such as a rail (not shown) laid in parallel with the common optical axis of the laser device 11, the beam expander 12, the convex lens 20, and the convex lens 21. As described above, a motor and other moving mechanisms are provided inside, and the movement of each can be controlled by the controller 26.

According to the apparatus having the above structure, the optical member 10
Is formed on the image pickup means by the image relay optical system 21 composed of the two convex lenses 21a and 21b for observation and analysis, so that the noise due to diffraction and the like is extremely small, so that the pattern due to the defect is clear. Can be identified. In addition, since the defect of each section of the optical member 10 can be detected independently, by performing appropriate image processing on the image of each section, it is possible to synthesize and evaluate a three-dimensional image of the defect, etc. Evaluation becomes possible. Moreover, since the configuration is relatively simple and the adjustment is relatively easy, there is an advantage that the manufacturing adjustment is easy.

Second Embodiment FIG. 2 is a diagram showing a main configuration of a second embodiment of the present invention. This embodiment is different from the first embodiment shown in FIG. 1 in that the vibrating device 20 is mounted on the upper end of the base 24a of the movable stage 24.
1 is provided to enable micro-vibration to be applied to the optical member 10, thereby improving the contrast of the defect image obtained by the CCD camera 22, and other configurations are the same as those of the first embodiment. is there. Therefore, in the following, the description will focus on the points that are unique to the present embodiment, and the portions common to the first embodiment will be assigned the same reference numerals and detailed description thereof will be omitted.

The vibration device 201 is composed of a piezo element or the like, and is driven and controlled by a controller 202. The controller 202 is controlled by a computer 28. The vibrating device 201 has a maximum amplitude of about several tens μm and a number of frequencies 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. A minute vibration of about several hundred Hz can be applied 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 has an amplitude of ± 20 μm (1 to 10 μm) and a frequency of 100H.
The measurement was performed while applying a small vibration of z. As a result, a very clear image of impurities and crystal growth stripes contained in the crystal could be obtained. In addition, impurities and crystal growth stripes inherent in the crystal are:
The refractive index difference is 10 ⁻⁵ to 10 ^{−6 with} respect to other normal parts
It is very difficult to obtain a clear image even with the apparatus of the first embodiment.

Third Embodiment FIG. 3 is a diagram showing a configuration of a main part of a third embodiment of the present invention. This embodiment uses a Newton-type beam expander 102 composed of two convex lens systems 102a and 102b instead of the beam expander 12 in the first embodiment shown in FIG. 1, and the vicinity of the focal point O of the convex lens system 102a. Place the rotating disk-shaped pick glass 301,
The laser beam emitted from the laser device 11 passes through the pickling glass 301 so that the beam expander 12
To reduce the coherence of the laser light emitted from the laser beam. As a result, a part of the laser beam R is
This is to prevent generation of noise due to an interference phenomenon caused by being reflected by an optical component such as an ND filter disposed on the front of the camera.

The ground glass 301 constitutes the coherence reducing means of the present invention. An optical glass such as BK-7 is formed in a disk shape having a thickness of 1 mm and a diameter of 50 mmφ. This was applied to form a pickpocket glass. The sand glass 301 can be rotated at a rotation speed of about 100 rpm by a motor 302 around the center of the disk as a center of rotation.
The point is located. That is, the position of the pickling glass at the point O is always changed, and the coherence is weakened by irregularities on the surface of the pickling glass at which the laser light passing through the pickling glass 301 changes randomly at the O point. . In addition, as the coherence reducing means, instead of the pickling glass 301, for example, a means in which an emulsion is dispersed in a transparent material or the like may be used as a means having the same effect.

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

FIG. 4 is a diagram showing a configuration of a main part of a fourth embodiment of the present invention. This embodiment enables an optical member 10 to be measured as it is without any pretreatment such as optical polishing or the like, and the optical member 10 is provided in a container 100 formed so as to allow light to pass therethrough. The container 100 is filled with the matching oil 101 and the container 100 is held on the movable stage 24 so that the optical member 10 is arranged at the same position as the optical member 10 in the first embodiment shown in FIG. It is like that.

Referring to FIG. 4, a container 100 has a substantially rectangular parallelepiped outer shape, a hollow box inside, and a pair of parallelly opposed light input portions arranged so as to be orthogonal to the traveling direction of the laser beam R.・ Emission windows 102 and 103 are made of optical glass such as BK-7 or fused silica, and other side walls are made of metal,
It is composed of plastics or the like. The light entrance / exit windows 102 and 103 have both surfaces sufficiently optically polished.

The optical member 10 is a non-pretreated N
It is a YAB crystal. Here, the pre-processing means the optical member 10
Before the measurement, the optical polishing is performed so that the light entrance and exit surfaces of the optical member 10 are parallel to each other and the shape is adjusted until a predetermined smoothness is obtained. Normally, if this pretreatment is not performed, reflection and refraction harmful to the measurement will occur due to unevenness of the light entrance / exit surface, making it difficult to obtain a defect image inside the crystal.

The matching oil 101 is used for the optical member 10
Of a substance having a refractive index substantially the same as that of When the optical member 10 is a NYAB crystal, the wavelength is 1.062 μm.
ordinary refractive index n ₀ for light of m is 1.7553, extraordinary refractive index n _e is 1.6869, the average refractive index n of about 1.70. Matching oil 10 of this refractive index
1 is obtained by mixing 1-chloronaphthalene and iodomethane at an appropriate mixing ratio.

By storing the optical member 10 in the container 100 and filling the optical member 10 with the matching oil 101, the matching oil 101 permeates and fills the uneven portions of the optical member 10. It is almost equal 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 performing a pre-process on the optical member 10.

In each of the above embodiments, a laser device is used as a light source for generating light that passes through the optical member. However, this is not necessarily a laser device. As long as it can be obtained, it is necessary to use a material having an appropriate wavelength according to the type of the optical member to be evaluated. For example, if the optical member is YIG (Y ₃ Fe
₅ O ₁₂ ) crystal, a He of wavelength 1.15 μm
A Ne laser device or a semiconductor laser device having a wavelength of 1.5 μm is used. In that case, as the imaging means,
Needless to say, a device having sensitivity to these wavelengths, for example, a CCD camera using a Ge crystal or the like is used.

In each of the above-described embodiments, a CCD camera is used as the imaging means, and the image signal sent from the CCD camera is processed by the computer and displayed on the display. Other imaging means may be used. It is not always necessary to use a computer as the information processing means, and the image transmitted from the imaging means may be directly displayed on a display.

[0046]

As described above, according to the present invention, the image relay optical system forms a cross-sectional image at a specific position inside the optical member outside the optical member, and this image is taken by the image pickup means. Accordingly, it is possible to obtain information of a cross-sectional image free of noise due to diffraction or the like, and to obtain an optical member evaluation apparatus that enables more accurate evaluation of an optical member.

[Brief description of the drawings]

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

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

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

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

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

FIG. 6 is a diagram showing a configuration of a device using a conventional Schlieren method.

[Explanation of symbols]

10 optical member, 11 laser device, 12 beam expander, 21 image relay optical system, 22 CCD
Cameras, 24, 25 movable stage, 26, 27 controller, 28 computer constituting information processing means, 29 display, 30 base, 201 vibration device, 301 pickpocket glass, 100 container, 101 ... Matching oil.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 21/84-21/958

Claims (6)

(57) [Claims] 1. A light source for generating light passing through an optical member, and a cross-sectional image at a specific position inside the optical member formed by light emitted from the light source and passing through the optical member is formed outside the optical member. a image relay optical system for the first convex lens of focal length disposed in the position of a rear position of the specific location distance d ₁ with respect to the specific position is f _1, and, first imaging the focal length to be combined with the convex lens an image of the specific position of the optical member and a second convex lens of f ₂ at a distance d ₂ a position of the backward with respect to the convex lens of the second D ₂ = (f ₂ / f ₁ ) (f ₁ + f ₂ ) − (f ₂ / f
An optical member comprising ₁₎ an image relay optical system having a 2 ^· d ₁ relationship, and an image pickup means disposed in the image forming point of the cross-sectional image of the specific position of the optical member formed by said image relay optical system Evaluation device. 2. The optical member evaluation device according to claim 1, further comprising a moving unit that changes a relative position of the optical member and the image pickup unit with respect to the image relay optical system. apparatus. 3. The optical member evaluation apparatus according to claim 2, wherein said image pickup means converts the picked-up image into a predetermined image signal and sends it out, and said image pickup means sent out from said image pickup means. An optical member evaluation apparatus, comprising: an information processing unit that inputs an image signal of an optical member and converts the image signal into information that can be evaluated. 4. The optical member evaluation device according to claim 1, further comprising a vibrating device for microvibrating the optical member. 5. The optical member evaluation apparatus according to claim 1, wherein the light emitted from the light source is coherent light, and the coherence is reduced to reduce the coherence. An optical member evaluation device 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 the container has substantially the same refractive index as the optical member. An optical member evaluation device, wherein a matching oil having a refractive index is filled.