JP3255589B2 - Lens 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 a lens evaluation apparatus, and more particularly to a lens evaluation apparatus suitable for evaluating a transmitted wavefront of a lens having a plurality of focal points.

[0002]

2. Description of the Related Art As a lens evaluation apparatus for evaluating a transmitted wavefront of a lens, an apparatus utilizing light interference is generally known. In such a lens evaluation device, for example, in a Fizeau interferometer, a test lens is set in a test optical path on which a reference surface is arranged, and the reference surface and the test lens are irradiated with laser light, so that the light from the test lens is The test light and the reference light from the reference surface are received, and an interference fringe generated by the received test light and the reference light is read by the imaging means. The read interference fringes are displayed on, for example, a television monitor after image processing. Then, based on the interference fringes displayed on the television monitor, it is possible to perform an evaluation such as a shape inspection of the lens to be inspected and a homogeneity inspection inside the lens.

[0003]

However, in the prior art, when evaluating a lens having a plurality of focal points, interference fringes as noise overlap with interference fringes displayed on a television monitor. , Evaluation becomes impossible. For example, when a hologram is formed on the lens surface and a laser beam is applied to a bifocal lens capable of focusing on two places to generate interference fringes, the television monitor displays the focus of the measurement target as shown in FIG. The interference fringes due to other focal points are superimposed and displayed on the interference fringes due to. When the two types of interference fringes are displayed as described above, the light intensity difference between the two interference fringes becomes small, and it becomes impossible to distinguish the interference fringes by the focus of the measurement target. As a result, there is a problem that it is not possible to accurately perform an evaluation such as a shape inspection of the lens to be inspected or a homogeneity inspection inside the lens.

The above-described lens evaluation device is also used for evaluating the inclination of an objective lens mounted on an optical information recording / reproducing device. In this case, however, there is a problem as described above. In addition, it is difficult to adjust the objective lens with high accuracy, and there is a problem that the adjustment operation also takes time.

It is an object of the present invention to provide a multifocal system having a plurality of focal points.
When evaluating a lens, even if an interference fringe based on a focus other than the measurement target as noise occurs on the interference fringe based on the focus of the measurement target, the influence of the noise can be easily removed to thereby reduce the interference. An object of the present invention is to provide a lens evaluation device capable of accurately performing an evaluation such as a shape inspection of an inspection lens and a homogeneity inspection inside a lens. It is another object of the present invention to provide a lens evaluation device capable of adjusting an objective lens and the like of an optical information recording / reproducing device with high accuracy.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 is based on a method in which a test light from a test lens set in a test optical path and a reference light from a reference optical path. the resulting interference pattern, read by the image pickup means provided on the light-receiving optical path, the interference fringe image processing, the lens evaluation apparatus for evaluating a lens from the processing result, the object
The inspection lens is a multifocal lens having a plurality of focal points, and is characterized in that a light amount attenuating optical member is provided in the middle of the light receiving optical path.

[0007] According to the above configuration, the test object having a plurality of focal points
When the lens is set in the optical path to be measured,
Interference fringes due to other focal points
The interference fringes due to the focus of the
Such noise can be easily attenuated or reduced by the
Can be removed, which allows the
Since a relatively large light intensity difference can be generated between the light amount of the displayed noise portion and the light amount of the interference fringe to be measured, it becomes easy to distinguish the interference fringe from the noise,
Noise can be easily removed from the interference fringes. As a result, it is possible to accurately evaluate the shape of the lens to be inspected and the homogeneity inspection inside the lens.

According to the second aspect of the present invention, the light amount attenuation
Optical member attenuates the amount of interference fringes as noise
It is characterized by having a light quantity attenuating section. This
Noise can be selectively removed.

According to a third aspect of the present invention, the light amount attenuating optical member is a light amount attenuating filter.

According to a fourth aspect of the present invention, an interference fringe generated by the test light from the test lens set in the test light path and the reference light from the reference light path is provided in an imaging device provided in the light receiving light path. Reading by said means, image processing said interference fringes,
In a lens evaluation apparatus for evaluating a lens from the processing result, the test lens is a multifocal lens having a plurality of focal points.
A's, the time of image processing said interference fringes, a portion to be a noise of the interference fringe mask is characterized in that a evaluating means for evaluating the portion other than the mask.

According to the above configuration, as described above, a plurality of
When a test lens with a focal point of
Interference fringes due to other focal points cause noise.
Such noise is easily removed by the optical element for light attenuation.
can do. Accordingly, when image processing is performed on the read interference fringes, the noise portion has been removed from the image processing target, so that the lens can be evaluated without being affected by the noise.

[0012]

When the evaluation is performed by the evaluation means,
If the masked portion is removed, the data amount of interference fringes may be reduced. Therefore, in the invention according to claim 5 , the evaluation means pseudo-creates an interference fringe of a masked portion based on interference fringes of a portion other than the masked portion, and adds the interference fringe to a result of the creation. It is characterized in that the test lens is evaluated. According to this configuration, the masked portion can be artificially supplemented with, for example, interference fringes approximated by a straight line or a broken line, and the accuracy of lens evaluation can be improved.

According to a sixth aspect of the present invention, the test lens is an objective lens mounted on an optical information recording / reproducing apparatus. When an objective lens is mounted on an optical information recording / reproducing apparatus, it is troublesome to adjust the inclination of the objective lens to an appropriate state.However, according to the lens evaluation apparatus of the present invention, the influence of noise is eliminated. , Because the interference fringes are clearly displayed on the TV monitor, etc.
The inclination of the objective lens can be easily adjusted. Also, in claim 7
In the invention described in the above, the lens evaluation device includes an image of interference fringes.
Corresponds to the focal length of the object to be measured by the multifocal lens.
The interference fringe image and noise corresponding to the focal length outside the measurement target
Corresponding to the multifocal lens containing the interference fringe image
Characterized by having an interference device that forms a cross-fringe image
I have. In the invention according to claim 8, the interference device
Is moved along the optical axis of the multifocal lens.
Focus to a position corresponding to each focus of the multifocal lens.
A concave mirror arranged so that the points coincide with each other, and the reference optical path
And the multifocal lens on the optical path to be detected.
Imaging interference fringes with the test light that passed through and was reflected by the concave mirror
The concave mirror as a measurement object.
Arrange the measurement so that the focal point matches the position corresponding to the focal point
It is characterized by being specified.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. Embodiment 1 FIG. 1 shows a schematic configuration of a lens evaluation apparatus according to the present invention. As shown in FIG. 1, the laser light from the laser light source 1 is expanded in beam width by a beam expander 2, further transmitted through a polarizing film 3 a of a polarizing beam splitter 3, and then converted from linearly polarized light by a quarter-wave plate 4 into a circle. The polarized light is guided to the collimator lens 5. The circularly polarized laser light is converted into a parallel light beam by the collimator lens 5 and travels along the optical path a to be detected.

A reference surface member 6 through which light can pass, a lens 7 to be tested, and a concave mirror 8 are arranged in the light path a to be tested. A part of the circularly polarized laser light traveling along the optical path a to be detected is reflected by the reference surface member 6. The reference surface member 6 has an entrance surface 6a and an exit surface 6b. The entrance surface 6a is provided perpendicular to the optical axis, and the exit surface 6b is provided at an angle. For this reason, of the circularly polarized laser light that has traveled along the test light path a, the laser light reflected on the incident surface 6a becomes reflected light and travels back through the test light path a, but is reflected on the output surface 6b. The emitted laser light is emitted in a direction deviating from the optical path a to be detected (in FIG. 1, a downward oblique direction). The laser light not reflected by the incident surface 6a and the outgoing surface 6b of the reference surface member 6 travels to the lens 7 to be measured.

A hologram 7a is formed on the surface of the lens 7 to be detected on the incident light side. When the test lens 7 is viewed from the reference surface member 6 side, the hologram 7a has a concentric circular shape and is formed at the center of the test lens 7,
Are not formed on the peripheral portion 7b of the. As a result, the test lens 7 can focus on two points, FA and FB. The light beam transmitted through the hologram 7a converges on the focal point FA, and its focal length is f1. The light beam transmitted through the peripheral portion 7b converges at the focal point FB, and the focal length is f2. Note that f1> f2.

Since the surface of the lens 7 to be inspected is not flat, the direction of reflection of the light reflected by the surfaces 7a and 7b of the lens 7 to be inspected does not become one direction, but the reflection traveling backward through the optical path a to be inspected. The amount of light has dropped considerably. Therefore, in the present embodiment, the test lens 7 is not reflected on the surface of the test lens 7
Is reflected by the concave mirror 8 and the laser light is added to the reflected light reflected on the surface of the lens 7 to be inspected, thereby preventing a decrease in the amount of reflected light traveling backward through the optical path a to be inspected. The concave mirror 8 is movable in the direction of arrow A in FIG. 1 so that the concave mirror 8 is arranged so that the focal point of the concave mirror 8 coincides with the focal point FA or FB of the lens 7 to be inspected.

The reflected light reflected by the incident surface 6a of the reference surface member 6 and the reflected light (including the reflected light reflected by the concave mirror 8) reflected by the surface of the lens 7 to be inspected go back through the optical path a to be inspected and collide. After passing through the meter lens 5, the light is converted from circularly polarized light into linearly polarized light by the 波長 wavelength plate 4 and guided to the polarization beam splitter 3. At this time, the direction of polarization of the reflected light guided to the polarization beam splitter 3 is changed by 90 degrees by the quarter wavelength plate 4 as compared with the case where the reflected light is emitted from the laser light source 1.

The reflected light guided to the polarizing beam splitter 3 has its path bent by 90 degrees by the polarizing film 3a, travels along the light receiving optical path b, and passes through the lens 9 disposed in the light receiving optical path b.
Is set to a predetermined magnification. At this time, the two reflected lights produce interference fringes, and the interference fringes are imaged by a television camera (or CCD) 10 as an imaging means. Then, the data of the interference fringes captured by the television camera 10 is taken into the image processing device 11, subjected to image processing, and displayed on the television monitor 12.

FIG. 2 shows the internal configuration of the image processing apparatus 11. In FIG. 2, a controller 11a is provided in the image processing apparatus 11, and the controller 11a controls the operation of the entire image processing apparatus 11. Controller 11
A keyboard 11b and a mouse 11c are connected to a, and data and commands can be input from the keyboard 11b and the mouse 11c. Further, the controller 11a includes a RAM 11d for storing data of interference fringes captured by the television camera 10, and a ROM 1 for storing a basic operation control program of the controller 11a.
1e is connected. The television camera 10 and the television monitor 12 are connected to the controller 11a.

In this embodiment, the light receiving optical path b
Is characterized in that the ND filter 13 is provided as an optical member for attenuating the amount of light in the middle of the process. FIG. 3 is a plan view of the ND filter 13. As shown in FIG. 3, in the ND filter 13, a filter pattern 13b is formed at a substantially central portion of a transparent plate member (for example, glass) 13a. The filter pattern 13b can be formed by vapor deposition or adhesion.

The ND filter 13 is connected to the light receiving optical path b
If the interference fringe due to the other focus of the test lens 7 overlaps with the interference fringe due to one focus of the test lens 7 to be measured as noise, the influence of the noise can be easily reduced. Can be removed.

If the ND filter 13 is provided in the middle of the light receiving optical path b, for example, as shown in FIG. 4, an interference fringe portion due to another focus is covered with the Nd filter 13, and the light amount of this interference fringe portion is reduced. Attenuated. For this, the TV camera 1
When image data of interference fringes read at 0 is processed by the image processing device 11, it is easy to distinguish between interference fringes and noise, and the influence of noise can be eliminated.

In FIG. 4, the filter pattern 13b has a small size that covers only the interference fringes due to the other focal point. However, as shown in FIG. 5, the filter pattern 13b has a large size that covers the entire light beam in the light receiving optical path b. Is also good. In this case, as shown in FIG. 6, the entire display area of the interference fringes due to the focus of the measurement target is covered with the filter pattern 13b '. When the reflected light passes through the ND filter 13, the entire light amount of the interference fringes is attenuated, but the contrast of the interference fringes due to other focal points is greatly reduced as compared with the original interference fringes due to the focus of the measurement target. For this reason, a light intensity difference occurs between the noise portion and the original interference fringes, so that the interference fringes can be easily distinguished from the noise, and the influence of the noise can be easily removed.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described. In the present embodiment, the light receiving optical path b
Instead of providing an optical member for attenuating the amount of light in the middle, software is used to remove the effect of noise. That is, the lens evaluation device of the present embodiment does not include the ND filter 13 in FIG. 1 and is configured to remove noise by software in the controller 11a in the processing device 11.

In order to remove noise by software, for example, as shown in FIG. 7, a portion where interference fringes due to other focal points are generated is masked by software, and only a portion other than the masked portion is removed by, for example, a television. It is displayed on the monitor 12. In this way, since the noise portion is completely eliminated, it is possible to evaluate the lens with almost no influence of the noise.

(Embodiment 3) Next, Embodiment 3 of the present invention will be described. This embodiment is also applicable to the second embodiment.
The effect of noise is removed using software in the same manner as in the above, but the feature is that a pseudo interference fringe is supplemented in the removed portion.

If the masked portion is excluded from the processing target, the amount of data as interference fringes at that portion will be reduced, which may cause a problem in evaluating the lens with high accuracy. Therefore, the lens evaluation device of the present embodiment pseudo-creates interference fringes in the masked portion (pseudo signal region) based on the interference fringes other than the masked portion as shown in FIG. The test lens is evaluated in consideration of the creation result.

As a method of simulating interference fringes in the pseudo signal area, there are a linear approximation, a broken line approximation, and the like. The straight-line approximation method is the simplest method, and it suffices to simply connect the original interference fringes separated by masking with a straight line in the pseudo signal region. The method of the polygonal line approximation is more complicated than the linear approximation, and the interference fringes in the pseudo signal region are obtained as a function by the least squares method from the data of the interference fringes in the unmasked portion. Display in the pseudo signal area. The process of artificially creating interference fringes in the pseudo signal region is performed by the controller 11a in the processing device 11.

According to the present embodiment, the portion excluded by masking can be artificially supplemented by interference fringes of linear approximation or broken line approximation, so that the accuracy of lens evaluation can be improved. .

In the first to third embodiments, the case where the lens evaluation apparatus of the present invention is applied to a Fizeau interferometer has been described as an example. However, the lens evaluation apparatus of the present invention is applicable to, for example, a sharing interferometer. Of course, it can be applied.

In the above-described first to third embodiments, only the case where the lens is evaluated has been described. However, the lens evaluation device of the present invention uses an objective having a plurality of focal points mounted on an optical information recording / reproducing device. It can also be applied to the case where the tilt of the lens is adjusted. For example, in FIG. 1, a light transmissive disk is provided as the reference surface member 6 and an objective lens is provided as the test lens 7, and the disk and the objective lens are irradiated with laser light to generate reflected light at that time. The interference fringes are read and subjected to image processing, and the interference fringes resulting from the image processing are displayed on a television monitor. And
The operator adjusts the tilt of the objective lens so that the interference fringes displayed on the television monitor are normal, that is, the interference fringes are substantially linear.

Further, in the first embodiment, the image picked up by the television camera 10 is binarized by a threshold value set based on the difference in the amount of light between the interference fringe to be measured and the interference fringe due to another focus. Stored in the RAM 11d (see FIG. 2),
Original interference fringes can be obtained from the stored contents. If the image is binarized and stored in the RAM 11d, it is easy to extract only the desired original interference fringes from the RAM 11d. Then, only the extracted original interference fringes are displayed on the television monitor 12.

[0035]

As described above, according to the present invention,
Even if noise occurs on the interference fringes, the interference fringes can be easily distinguished from the noise, and the noise can be easily removed from the interference fringes. As a result, it is possible to accurately evaluate the shape of the lens to be inspected and the homogeneity inspection inside the lens.

Further, the use of the lens evaluation device of the present invention makes it possible to adjust the objective lens and the like mounted on the optical information recording / reproducing device with high accuracy.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a lens evaluation device according to the present invention.

FIG. 2 is an internal configuration diagram of an image processing device mounted on the lens evaluation device of FIG. 1;

FIG. 3 shows ND for dimming only a noise portion of interference fringes.
It is a top view of a filter.

FIG. 4 is a diagram showing a state when interference fringes are covered by the ND filter of FIG. 3;

FIG. 5 is a plan view of an ND filter for dimming the entire light beam in the light receiving optical path.

6 is a diagram showing a state when interference fringes are covered by the ND filter of FIG. 5;

FIG. 7 is a diagram showing a state when only a noise portion of an interference fringe is masked.

FIG. 8 is a diagram showing a state where a masked portion is corrected with a pseudo interference fringe.

FIG. 9 is a diagram showing a state in which interference fringes as noise overlap with interference fringes to be measured.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Beam expander 3 Polarization beam splitter 4 1/4 wavelength plate 5 Collimator lens 6 Reference surface member 7 Test lens 8 Concave mirror 9 Lens 10 Television camera (or CCD) 11 Image processing device 12 Television monitor 13 ND filter a Optical path to be tested b Light receiving path

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-109582 (JP, A) JP-A-61-126403 (JP, A) JP-A-61-272605 (JP, A) JP-A-6-106605 258181 (JP, A) JP-A-62-225921 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 11/00-11/08

Claims (8)

(57) [Claims] 1. An interference fringe generated by a test light from a test lens set in a test optical path and a reference light from a reference optical path is read by an image pickup means provided in a light receiving optical path, and the interference fringes are imaged. In a lens evaluation apparatus that performs processing and evaluates a lens based on the processing result, the test lens is a multifocal lens having a plurality of focal points.
A light amount attenuation optical member is provided in the light receiving optical path. 2. The lens evaluation device according to claim 1, wherein the optical member for attenuating the light amount includes light of interference fringes as noise.
Characterized by having a light quantity attenuating section for attenuating the quantity.
Evaluation device. 3. The lens evaluation device according to claim 1, wherein the light amount attenuation optical member is a light amount attenuation filter. 4. An interference fringe generated by the test light from the test lens set on the test optical path and the reference light from the reference optical path is read by an image pickup means provided on the light receiving optical path, and the interference fringe is imaged. In a lens evaluation apparatus that performs processing and evaluates a lens based on the processing result, the test lens is a multifocal lens having a plurality of focal points.
Ri, when the image processing said interference fringes, a portion to be a noise of the interference fringe mask, the lens evaluation apparatus characterized by comprising an evaluation means for evaluating the portion other than the mask. 5. The lens evaluation apparatus according to claim 4 , wherein said evaluation means pseudo-creates an interference fringe of a masked portion based on an interference fringe of a portion other than the masked portion, and generates the result. A lens evaluation device that evaluates the test lens in consideration of the following. 6. The lens evaluation device according to any one of claims 1 to 5, wherein the test lens is a lens evaluation device, characterized in that the objective lens mounted in an optical information recording and reproducing apparatus. 7. The lens according to claim 1,
In the evaluation device, the lens evaluation device may include an image of interference fringes.
The image corresponds to the focal length of the measurement object of the multifocal lens
Noise corresponding to the interference fringe image and the focal length outside the measurement target
Compatible with multifocal lenses including interference fringe images as
An interference device for forming an interference fringe image is provided.
Lens evaluation device. 8. The lens evaluation device according to claim 7, wherein
hand, By moving along the optical axis of the multifocal lens,
The focal point is located at a position corresponding to each focal point of the multifocal lens.
A concave mirror arranged to coincide with the reference light path;
Passing through the multifocal lens on the test light path with the reference light of
Imaging interference fringes with the test light reflected by the concave mirror
Imaging means, wherein the concave mirror is a focal point as a measurement object.
Is positioned so that the focal point matches the position corresponding to
A lens evaluation device.