JPH06317413A - Interferometer device for inspecting optical member - Google Patents

Abstract

PURPOSE:To inspect lenses and other optical members for their surface shapes and optical performances even if they have antireflection coatings. CONSTITUTION:At the time of inspecting a lens 7 having such an antireflection coating that the reflectivity of the lens can become nearly zero in the wavelength range of 600-700nm, the wavelength of the light made incident to a reference lens 6 is selected by using an He-Ne laser which emits a laser beam in a transmissive wavelength region as a first laser oscillator 1a and an Ar laser which emits a laser beam in a wavelength region in which part of the laser light is reflected as a second laser oscillator 1b and respectively installing shutters 12a and 12b to the optical paths from the oscillators 1a and 1b. When the shutter 12a is opened, part of the laser beam from the oscillator 1a is reflected by the reference surface 6a of the lens 6 and the other part of the laser beam is reflected by a reflecting plate 10 after the part is transmitted through a lens 7 to be inspected from the surface 6a. As a result, interference fringes in which the wave front of the other part reflected by the plate 10 overlaps that of the light reflected by the surface 6a are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member inspection interference for inspecting various characteristics of an optical member, such as a lens and a plate-shaped optical member, in a finished product state using a laser interferometer. It relates to a measuring device.

[0002]

2. Description of the Related Art A laser interferometer for inspecting lenses and other optical members reflects a part of laser light emitted from a laser light source on a reference surface, and a wavefront of this reflected light,
The wavefront of the light from the optical member to be inspected is superposed and the interference fringes generated between both wavefronts are observed. Here, by using a laser interferometer,
Along with the measurement of the surface shape of the optical member, the inspection of the optical performance such as aberration can be performed. The surface shape of the optical member is measured by reflecting the laser light on the member to be inspected, superposing the wavefront of this reflected light and the wavefront of the reflected light from the reference surface, and observing the interference fringes generated between both wavefronts. It can be done by On the other hand, the laser beam is transmitted through the member to be inspected, the wave front of the transmitted light and the wave front of the reflected light from the reference surface are superposed, and the interference fringes generated between the both wave fronts are observed. Inspection of optical performances can be performed.

[0003]

By the way, in an optical disk device or the like, an optical pickup is used to read information written on the optical disk. This optical pickup has a laser light source, and the laser light emitted from this laser light source is made to enter a track in which information is written by narrowing down the spot diameter by an objective lens, but the light passing through this objective lens is Due to the high coherence, an antireflection coating is applied to the laser light entrance / exit surface in order to prevent noise such as ghost occurrence from occurring.

Here, the quality inspection performed after manufacturing the objective lens can be performed using the interferometer device as described above. However, since the surface of this objective lens is coated with an antireflection coating, the inspection based on the transmitted wavefront of the lens can be performed, but the light emitted to the lens cannot be reflected. Therefore, the surface shape of the lens cannot be inspected based on the reflected wavefront. Therefore, conventionally, the surface shape of such a lens is generally inspected before the antireflection coating is applied, and then the inspection by the transmitted wavefront is applied after the antireflection coating is applied. Is. As a result,
Depending on the interferometer device, there is a problem that a comprehensive inspection including shape measurement cannot be performed at the stage of a finished product after the antireflection coating is applied as a lens.

The present invention has been made in view of the above points, and it is an object of the present invention to obtain the surface shape and optical performance of a lens or other optical member to be tested even after an antireflection coating is applied. It is to be able to carry out an inspection.

[0006]

In order to achieve the above-mentioned object, the present invention provides a transmission of an antireflection coating for inspecting an optical member having a coating for preventing reflection of light in a specific wavelength region. A first laser light source that oscillates in the wavelength range, a second laser light source that oscillates in the reflection wavelength range, and laser light from these two light sources are selectively incident to reflect a part of the incident light. , A reference surface for transmitting the other part and a reference reflecting member for reflecting the transmitted light from the optical member to be inspected, and the light from the first laser light source passes through the optical member to be inspected and is subjected to the reference reflection. Interference fringe image generated between the wavefront of the transmitted light reflected by the member and the wavefront of the reflected light from the reference surface, and the reflected light wavefront and the reference surface of the light from the second laser light source reflected on the surface of the optical member to be tested. Between the wave front of the reflected light from It is an its features that it has an observation configurable and fringe image.

[0007]

For example, the antireflection coating applied to the objective lens used in the optical pickup has wavelength selectivity. That is, it is generally the case that the transmittance is highest in the oscillation wavelength region of the light source incident on the objective lens, and that light having a wavelength outside this wavelength region is reflected to some extent. Therefore, two types of laser light sources having different wavelengths are used as the light sources mounted on the interferometer device.
As the first laser light source, one that oscillates in the transmission wavelength region of the antireflection coating of the lens to be inspected is used, and as the second laser light source, one that oscillates in the wavelength region in which the reflectance of the antireflection coating is high.

When the optical member to be inspected is a lens, this lens to be inspected is set at a predetermined position of the interferometer and the illumination light from the first laser light source or the second laser light source is selected. Incident on the reference lens. For example, first, the light from the first laser light source is incident on the reference lens, and a part of the light is reflected by the reference surface of the reference lens and a part of the light is transmitted. The light that has passed through the reference lens is incident on the lens to be inspected, but since the lens to be inspected has an antireflection coating, almost all the light flux incident on the lens to be inspected passes through the lens to be inspected. And is reflected by the reference reflecting member. The light reflected by the reference reflection member in this way passes through the lens to be inspected again, and the wavefront overlaps the reflected light on the reference surface of the reference lens. Then, interference fringes can be observed by the interference action of both wavefronts. With this, it is possible to inspect the wavefront aberration such as astigmatism, coma and spherical aberration, and the optical performance of the lens such as spot diagram, point image intensity distribution and MTF. Here, in order to inspect the optical performance of such a lens, it is necessary to inspect at the wavelength used,
For this reason, it is preferable to use, as the first laser light source, one having a wavelength light which is actually incident on the lens.

Next, the light source is switched to make the laser light from the second laser light source incident on the reference lens. Since the oscillation wavelength of the second laser light source is in the wavelength range in which the reflectance of the antireflection coating applied to the lens under test is high, this incident light is reflected by the surface under test of the lens under test. The two wavefronts of the reflected light from the surface to be inspected and the reflected light on the reference surface of the reference lens can be superposed and the interference fringes resulting from the overlapping of the wavefronts can be observed. This makes it possible to determine whether or not the surface shape of the lens under test is in a predetermined state. Here, when measuring the surface shape of the lens to be inspected, no special support is given regardless of the wavelength region.

As described above, only by switching the light source, after forming the antireflection coating, there are two kinds of inspections, that is, the inspection based on the transmitted wavefront of the lens to be inspected and the inspection based on the reflected wavefront on the surface of the lens to be inspected. Since a single interferometer device can be used for the inspection of 1., a comprehensive inspection can be easily performed on the surface shape and optical characteristics of the lens to be inspected when it is a finished product.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. First, FIGS. 1 and 2 show the configuration of an optical system in an interferometer device. In the figure, 1a, 1b
Indicates a laser oscillator, and the laser light emitted from the laser oscillators 1a and 1b is selectively made incident on the diverging lens 2 by a light source selecting means described later.
The divergence lens 2 is for expanding the beam diameter of the laser light to an extent necessary for inspection.
The laser light that has passed through is once condensed and then diverged. A pinhole 3 is provided at this light collecting position so that obstructive light is removed from the optical path. The light passing through the pinhole 3 is incident on the beam splitter 4 while diverging, and its reflecting surface 4a
The light path is bent by 90 °. The light reflected by the beam splitter 4 is collimated by the collimator lens 5 at a position where the beam has a predetermined beam diameter.

The light collimated by the collimator lens 5 is incident on the reference lens 6. The reference lens 6 is arranged at the front position of the collimator lens 5, and the surfaces of the respective lenses constituting the reference lens 6 are provided with antireflection coating, but the final emission surface is the uncoated reference surface 6a. There is. A lens 7 to be inspected as an object to be inspected is arranged in front of the reference lens 6, and light transmitted through the reference lens 6 is incident on a surface 7a to be inspected of the lens 7 to be inspected. . Further, at a position below the lens 7 to be inspected,
A reflection plate 10 that reflects the light transmitted through the lens 7 to be inspected is provided. Denoted at 8 is an imaging lens, and 9 is an image pickup means. Depending on whether the laser oscillator 1a or the laser oscillator 1b is used as a light source, the wavefront of the transmitted light of the lens 7 to be inspected or the lens 7 to be inspected is inspected. Interference fringes produced by the wavefront of the reflected light on the surface 7a and the wavefront of the reflected light from the reference surface 6a on the reference lens 6 are imaged on the image pickup means 9 via the imaging lens 8, and the interference fringes are formed. The image is displayed on a monitor device (not shown).

Here, the lens 7 to be inspected is used, for example, as an objective lens in an optical pickup, and in the finished product, the surface 7a to be inspected has an antireflection coating. As the light source of the optical pickup,
When using a He-Ne laser, the oscillation wavelength is 6
Since it is 32.8 nm, as shown in FIG.
An antireflection coating is used which has a reflectance of almost 0 at ˜700 nm. This anti-reflective coating is 60
Although it has some reflectance at wavelengths of 0 nm or less and 700 nm or more, it does not cause any particular problem in use. Therefore, if a He-Ne laser is used as the light source of the interferometer device, almost all the light incident on the lens 7 to be inspected passes through the lens 7 to be inspected. On the other hand, the wavelength of Ar laser is 48
It is 8.0 nm, and at this wavelength, even if the antireflection coating is applied, there is a reflectance close to the surface reflection of the lens under test in the uncoated state. Therefore, if this Ar laser is used as a light source, a reflected wavefront from the surface 7a to be measured of the lens 7 to be measured can be obtained.

Therefore, the first laser oscillator 1a is He-
Ne laser is used, and A is used in the second laser oscillator 1b.
r laser is used. Then, in order to select the output light from these first and second laser oscillators 1a and 1b, a shutter 12a as a light source selecting means is provided on the output side thereof.
12b is provided, and both laser oscillators 1a and 1a are provided.
A reflection mirror 13 and a mirror 14 having a wavelength selection characteristic are used to unify the optical path from b. Therefore, the first
The laser light from the laser oscillator 1a of
The light is transmitted through the mirror 14 and is guided to the diverging lens 2. Further, the laser light from the second laser oscillator 1b can be guided to the diverging lens 2 by first reflecting on the reflecting mirror 13 via the shutter 12b and then also reflecting on the mirror 14.

The present embodiment is configured as described above, and by using this interferometer device, after the antireflection coating is applied to the surface 7a of the lens 7 to be inspected, the object 7 to be inspected is coated. The transmitted wavefront and the reflected wavefront of the inspection lens 7 and the reflected wavefront from the reference surface 6a of the reference lens 6 are overlapped with each other, and interference fringes can be formed by the interference action therebetween, and the interference fringes can be imaged by the imaging means 9.

As shown in FIG. 1, the laser oscillators 1a and 1b are both kept in an oscillating state. First, the shutter 12a is opened and the shutter 12b is kept in the closed state, and the lens 7 to be inspected. Is arranged at a position for inspecting the characteristics of the reference lens 6 by transmission, that is, at a position where the transmitted light from the lens 7 to be inspected becomes substantially parallel light. by this,
The laser light from the first laser oscillator 1a is incident on the diverging lens 2 via the mirror 14 and, after passing through the pinhole 3 to remove disturbing light, is reflected on the reflecting surface 4a of the beam splitter 4. And the optical path is 90 °
The light is bent, enters the collimator lens 5, and is converted into a parallel light flux. The parallel light flux is incident on the reference lens 6, a part of which is reflected by the reference surface 6a of the reference lens 6, and the other part of which is transmitted through the reference surface 6a. The light transmitted through the reference surface 6a is incident on the lens 7 to be inspected, and both surfaces of the lens 7 to be inspected are coated with an antireflection coating having a reflectance of approximately 0 at 600 to 700 nm. Oscillator 1
Since the oscillation wavelength of a is 632.8 nm, most of the incident light is transmitted through the lens 7 to be inspected, but at that time, it is substantially parallel light. The light transmitted through the lens 7 to be inspected is reflected by the reflection plate 10 and the optical path is reversed. The light reflected by the reflecting plate 10 and the light reflected by the reference surface 6a of the reference lens 6 pass through the reflecting surface 4a of the beam splitter 4 and are guided to the image pickup means 9 via the imaging lens 8. The interference fringes are imaged on the image pickup means 9 by superposing the wavefronts of the two reflected lights. By observing this interference fringe, it is possible to inspect the optical characteristics, aberration characteristics, etc. of the lens 7 to be inspected.

Since the laser light from the He--Ne laser is incident when the lens 7 to be inspected is incorporated in a predetermined product, the light to be inspected using the light in the wavelength region actually used. By inspecting the optical performance of the lens 7, it is possible to accurately inspect the optical performance of the lens. Moreover, since the light transmitted through the lens 7 to be inspected is substantially parallel light, the aberration characteristic can be inspected more accurately.

Next, as shown in FIG.
By closing a and opening the shutter 12b,
The laser light from the second laser oscillator 1b made of an Ar laser having a wavelength of 488.0 nm is guided to the optical path, and the lens 7 to be inspected is displaced to a position suitable for the inspection by reflection. As a result, a part of the laser light reflected from the second laser oscillator 1b to the reflection mirror 13 and the mirror 14 is reflected on the reference surface 6a of the reference lens 6 and a part thereof is transmitted. The transmitted light of the reference lens 6 is incident on the surface 7a of the lens 7 to be inspected. Although the surface 7a to be inspected has an antireflection coating, the light from the second laser oscillator 1b is 488. It has a wavelength of 0.0 nm, and a part of the wavelength is reflected by the antireflection coating at this wavelength. Therefore, by superimposing the reflected light from the surface 7a to be tested with the reflected light from the reference surface 6a of the reference lens 6, the image pickup means 9 has an interference fringe corresponding to the shape of the surface 7a to be tested of the lens 7. The surface 7a of the lens 7 to be inspected is observed.
The surface shape of the is measured. In this case, although it is different from the wavelength of the light that is actually incident on the surface 7a to be inspected of the lens 7 to be inspected, the wavelength of the light to be incident on the lens 7 to be inspected is because the surface shape is measured. Has no restrictions.

As described above, by using the laser oscillators 1a and 1b which emit light of two types of wavelengths, it is possible to perform an inspection based on each wavefront of reflection and transmission of the lens 7 to be inspected. However, since two types of laser light having different wavelengths are used, the optical system that constitutes the interferometer device uses a diverging lens 2, a collimator lens 5, and a reference lens so that aberrations do not occur in the light of these two types of regions. The lens 6 and the like must have predetermined characteristics. Also, the antireflection coating formed on these optical members must be selected so that light of these two wavelengths is transmitted. With these, various aberrations with respect to the light of both wavelengths can be suppressed, and ghost, noise and the like will not occur.

Although the He-Ne laser is used as the first laser oscillator 1a and the Ar laser is used as the second laser oscillator 1b in the above-described embodiment, the transmission wavelength characteristic of the antireflection coating is used. Is 600-7
This is due to the fact that the reflectance is almost 0 at 00 nm. The point is that a laser oscillator that oscillates in the transmission wavelength range and a laser that oscillates in the reflection wavelength range according to the wavelength characteristics of the antireflection coating. An oscillator may be used. Further, the light source selecting means may be constituted by not only the above-mentioned shutter but also means for moving the laser oscillators 1a and 1b in a direction orthogonal to the optical path, or inserting / removing the mirror 14 into / from the optical path. .
In addition, although the lens has been described as an example of the optical member to be inspected, a plate-shaped optical member such as a window or a prism may be used in addition to this, and in this case, a reference surface having a reference surface is provided. A reference plane is used instead of a lens.

[0021]

As described above, according to the present invention, the first laser light source oscillating in the transmission wavelength region of the antireflection coating formed on the lens to be inspected and the second laser light source oscillating in the reflection wavelength region are provided. By using two light sources, the laser light from these light sources is selectively made incident on the reference lens so that a part thereof is reflected and the other part is transmitted, and this transmitted light is made incident on the lens to be inspected. , The laser light from the first laser light source is transmitted through the lens to be inspected and reflected by the reference reflection member to form an interference fringe image between the transmitted light wavefront and the wavefront of the reflected light from the reference surface. In addition to being observable, the light from the second laser light source is reflected on the surface of the lens to be inspected, and the interference fringe image generated between this reflected light wavefront and the wavefront of the reflected light from the reference surface can be observed. So, switching light source is a simple interference At the stage of the finished product with the anti-reflection coating formed by using the device, there are two types of inspections, that is, the inspection based on the transmitted wave front of the lens to be inspected and the inspection based on the reflected wave front on the surface of the lens to be inspected. It is possible to perform the comprehensive inspection of the lens to be inspected easily.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an optical system of an interferometer device showing an embodiment of the present invention, and is a diagram showing an inspection state of optical characteristics by transmission of a lens to be inspected.

FIG. 2 is an explanatory view similar to FIG. 1, showing an inspection state of a surface shape of a lens to be inspected.

FIG. 3 is a diagram showing a wavelength transmittance of an antireflection coating applied to a surface to be inspected of a lens to be inspected.

[Explanation of symbols]

 1a 1st laser oscillator 1b 2nd laser oscillator 6 Reference lens 6a Reference surface 7 Test lens 7a Test surface 10 Reference reflection member 12a, 12b Shutter

Claims (1)

[Claims] 1. A first laser light source that oscillates in a transmission wavelength range of the antireflection coating and an oscillation in a reflection wavelength range for inspecting an optical member coated with a coating that prevents reflection of light in a specific wavelength range. A second laser light source, a reference surface on which the laser light from these two light sources is selectively incident, a part of the incident light is reflected, and the other part is transmitted; A reference reflection member that reflects the transmitted light of the first laser light source, the light from the first laser light source is transmitted through the optical member to be tested and reflected by the reference reflection member, and the wavefront of the reflected light from the reference surface. And an interference fringe image generated between the wavefront of the reflected light from the surface of the optical member to be measured and the wavefront of the reflected light from the reference surface. Of the optical member characterized by having a possible configuration Inspection interferometer device.