JPH08334606A - Lens - Google Patents

Abstract

PURPOSE: To easily and rapidly adjust a lens tilt correction in the measurement of the lens with an interferometer. CONSTITUTION: The lens is formed to such a shape that an area outside the effective diameter 12 of a 1st plane 1 may return reflected light F1 which is parallel to an optical axis A with reference to incident light L which is parallel to the optical axis A, and also, the lens is formed to such a shape that the light F2 reflected by a 2nd plane 2 may not cause the interference with the light F1 reflected by the 1st plane, because the flat part 23 in the area outside the effective diameter 22 of the 2nd plane 2 is constituted of such a plane that is not perpendicular to the optical axis A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring a wavefront aberration by a lens interferometer, and more particularly to the shape of an objective lens or a collimator lens for an optical pickup used in an optical disk device.

[0002]

2. Description of the Related Art In recent years, in order to improve the performance of an optical disk device, the performance of a lens used in an optical pickup, which is a basic component of the optical disk device, has been very important. As a method of measuring the performance of a lens used in a laser optical system, a method of measuring a transmitted wavefront aberration based on the principle of a Fizeau interferometer as shown in FIG. 3 is often used. Generally, when measuring the lens with an interferometer, if the position of the lens is mechanically adjusted, the tilt of the entire lens becomes large, and there is a limit to the accuracy particularly in the coma aberration measurement. Therefore, in an interferometer based on the principle of being able to acquire the reflected light of the lens to be inspected, such as a Fizeau interferometer, it is possible to arrange the flat portion perpendicular to the optical axis by aligning the interference fringes of the reflected light from the flat portion. It is possible.

This adjusting method and a conventional lens will be described below with reference to the drawings. 3 is a schematic diagram showing the principle of a Fizeau interferometer, FIG. 4 is an optical path diagram when a conventional lens is applied to a Fizeau interferometer, FIG. 5 is an explanatory diagram of interference fringes due to direct reflected light, and FIG. 6 is a conventional lens FIG. 7 is an explanatory diagram of interference fringes due to reflected light by the light source. In FIG. 3, the light emitted from the laser 31 passes through the polarization beam splitter 32 and becomes a parallel beam at the collimator lens 33. This parallel beam is 1 /
The four-wave plate 35 and the transmission plane 35 are transmitted through the lens 36 to be measured.
The transmitted light is reflected by the reference spherical surface 37 which is adjusted and installed at an appropriate position. The reflected light takes an optical path opposite to the above-mentioned optical path together with the reflected light on the flat surface of the lens to be inspected, is reflected by the polarization beam splitter 32, and is applied to the photodetector 38. The interference fringes can be seen by outputting the output of the photodetector 38 to an adjustment monitor (not shown) or the like.

Here, if the reference spherical surface 37 is removed so that the transmitted light of the lens 36 to be inspected does not return while being transmitted as it is, only the light reflected by the flat surface of the lens 36 to be inspected irradiates the photodetector 38 as described above. To be done. FIG.
, 11 is an effective diameter region of the first surface 1 of the lens, and 12
Denotes an outer-effective-diameter region, 13 denotes a flat portion, which is a surface perpendicular to the optical axis A of the lens and is provided in the outer-effective-diameter region 12. Similarly, 21 is an effective diameter area of the second surface 2 of the lens, 22 is an effective diameter outside area, 25 is a flat portion, which is a surface perpendicular to the optical axis A of the lens, and is an effective diameter outside area 22. It is provided in.

The tilt adjustment by the Fizeau interferometer shown in FIG. 3 of the conventional lens thus constructed will be described below with reference to FIGS. 3 to 6. First as shown in FIG.
If the flat portion 13 is provided in the area 12 outside the effective diameter of the surface 1 and is machined with high accuracy so as to be perpendicular to the optical axis A, the flatness is adjusted by the Fizeau interferometer adjustment method (excluding the reference spherical surface) in FIG. Interference fringe 5 due to the reflected light F1 at the portion 13
By adjusting the position so that (FIG. 5) disappears, the tilt of the lens can be suppressed to the wavelength unit.

[0006]

In the above adjusting method, the degree of disappearance of the interference fringes 5 determines the accuracy of the position adjustment, and therefore it is desirable that the state is clear as shown in FIG. However, in the conventional lens, the flat portion 25 of the outer effective diameter region 22 of the second surface is perpendicular to the optical axis A, so that the optical axis A
The incident light L parallel to the optical axis A is reflected parallel to the optical axis A, and the interference fringes 5 due to the reflected light F1 on the flat portion 13 of the first surface 1 and the flat portion 25 of the second surface 2 are reflected as shown in FIG. Light reflected at F
False interference fringes 6 due to 2 are generated and appear to be overlapped on the adjustment monitor. The false interference fringes 6 can be distinguished at a glance because they do not change with a minute lens adjustment, but it is very difficult to judge whether or not the true interference fringes 5 have completely disappeared.

The present invention solves the above problems,
It is intended to prevent the occurrence of false interference fringes 6 that hinder the adjustment of the interference fringes 5.

[0008]

In order to achieve this object, in the present invention, for incident light parallel to the optical axis of the lens,
The first outside of the effective diameter region of the lens returns the first reflected light parallel to the optical axis, and the second outside of the effective diameter region of the second surface of the lens
It is configured so that the reflected light does not interfere with the first reflected light, and in particular, the flat surface in the area outside the effective diameter of the second surface is formed so as to have an inclination with respect to the optical axis. .

Further, the area outside the effective diameter of the second surface is formed so as not to return reflected light.

[0010]

According to the present invention, due to the above-mentioned shape, the reflected light from the area outside the effective diameter of the second surface does not become parallel to the optical axis, or the reflected light does not occur, so that interference fringes that hinder the tilt adjustment of the lens. Can be prevented and a clearer view can be obtained on the adjustment monitor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 23 is the second surface 2
Side flat portion, which is the outer effective diameter region 22 of the second surface 2.
Is provided for the flat portion 13 of the first surface 1, for example, 5
It is formed to have a degree of inclination. The other components are the same as in the conventional example.

A case in which the lens of the present invention having such a structure is measured by the above-mentioned adjustment method using the Fizeau interferometer will be described. As shown in FIG. 1, since the flat portion 13 perpendicular to the optical axis A is provided in the outer effective diameter region 12 of the first surface 1 of the lens as in the conventional example, the incident light L parallel to the optical axis A is formed. On the other hand, since the reflected light F1 parallel to the optical axis A is returned, an interference fringe for tilt adjustment is generated. At the same time, since the flat portion 23 of the effective outer diameter area 22 of the second surface 2 is formed so as to have an inclination of 5 degrees with respect to the flat portion 13 of the first surface 1, the reflected light F2 thereof is directed to the optical axis A. Not parallel,
It is possible to prevent the occurrence of interference fringes that hinder the tilt adjustment of the lens.

As described above, according to the first embodiment of the present invention, since the reflected light from the flat portion of the second surface is not parallel to the optical axis, it is not detected by the principle of the Fizeau interferometer and the false interference fringes are not detected. Does not occur. Further, since the flat portion of the second surface can be easily molded at the same time in the lens production process, the cost can be reduced. The second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view of a lens according to the second embodiment of the present invention.

In FIG. 2, reference numeral 24 is a flat portion provided in the effective outer region 22 of the second surface 2, the surface roughness of which is roughly shaped like ground glass, and light is transmitted and reflected on this surface. Does not cause The other components are the same as those in the first embodiment. When the Fizeau interferometer is used to measure the lens of the second embodiment having the above-described configuration in the same manner as described above, the incident light L incident parallel to the optical axis A is the first
The flat portion of the surface reflects parallel to the optical axis A, but the flat portion of the second surface, which has a rough surface roughness, does not cause reflection.
The Fizeau interferometer does not generate false interference fringes due to the reflected light from the second surface.

As described above, according to the second embodiment of the present invention,
The first surface is reflected in parallel, but the second surface is not reflected at all, and no false interference fringes are generated. Further, in the second embodiment, the flat portion of the second surface can be a surface perpendicular to the optical axis, which simplifies the mold construction for producing the lens. The second
In the embodiment, even if an antireflection film is applied to the area outside the effective diameter of the second surface so that the reflected light does not return, reflection does not occur in the area outside the effective diameter of the second surface, and the same effect can be obtained. To be

Further, by combining the first embodiment and the second embodiment, the flat portion in the area outside the effective diameter of the second surface is angled with respect to the optical axis, and reflection is not caused. The surface roughness may be roughened or an antireflection film may be applied.

[0017]

As described above, according to the present invention, with respect to the incident light parallel to the optical axis of the lens, the first reflected light whose effective outer diameter area of the first surface of the lens is parallel to the optical axis is returned. In addition, the second reflected light in the area outside the effective diameter of the second surface of the lens is configured not to interfere with the first reflected light, and in particular, the flat surface in the area outside the effective diameter of the second surface is Since it is formed so as to have an inclination with respect to the axis or the effective outer diameter area of the second surface is formed so as not to return reflected light, the second surface is effective even in the adjustment method using the Fizeau interferometer. False interference fringes due to reflected light from the outer diameter region do not occur, only true interference fringes due to reflected light from the first flat surface are minimized, and lens tilt, which is the main factor of wavefront aberration error, is minimized. It is possible to hold down and measure quickly.

[Brief description of drawings]

FIG. 1 is a diagram showing a lens shape and a reflected light path according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a lens shape and a reflected light path according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing the principle of a Fizeau interferometer.

FIG. 4 is a diagram showing a conventional lens shape and a reflected light path.

FIG. 5 is a schematic diagram of interference fringes due to reflected light at the flat portion of the first surface.

FIG. 6 is a schematic diagram of interference fringes due to reflected light from a first-surface flat portion and a second-surface flat portion.

[Explanation of symbols]

 1 1st surface 2 2nd surface 5 Interference fringes 6 False interference fringes 12 1st surface outside effective diameter area 13 1st surface side flat part 22 2nd surface outside effective diameter area 23 2nd surface side flat part A Optical axis L incidence Light F1 Reflected light F2 Reflected light

Claims (3)

[Claims] 1. For incident light parallel to the optical axis of the lens,
The outer-effective-diameter region of the first surface of the lens returns the first reflected light parallel to the optical axis, and the second-reflected light in the outer-effective-diameter region of the second surface of the lens is the first reflected light. A lens characterized by being configured so as not to cause interference. 2. The flat surface in the effective outer diameter region of the second surface,
The lens according to claim 1, wherein the lens is formed so as to have an inclination with respect to the optical axis. 3. The lens according to claim 1, wherein the area outside the effective diameter of the second surface is formed so as not to return reflected light.