JPS62147339A - Apparatus for inspecting optical axis of lens - Google Patents

Abstract

PURPOSE:To make it possible to directly measure the inclination of the optical axis of a lens to be inspected, by observing the strain of the wave front transmitted through the lens to be inspected as an interference fringe. CONSTITUTION:Parallel beam transmits through a first beam splitter 2 and separated into reflected beam and transmitted beam by a reference plate 3. Transmitted beam is reflected by a second beam splitter 4 to be vertically incident to a reference stand 5 and the beam vertically emitted from the reference stand 5 is incident to a lens 6 to be inspected to be formed into an image on a reflective surface 7. The beam reflected from the reflective surface 7 is further separated into reflected beam and transmitted beam by the splitter 2 and the reflected beam transmits through the plate 3 to be reflected by the splitter 2 and incident to an image pickup apparatus 9 through a luminous flux converting lens 8. The reflected beam from the plate 3 is similarly reflected by the splitter 2 to be incident to the apparatus 9 through the lens 8. These incident beams generate an interference fringe which can be, in turn, observed on a display device. The beam transmitted through the splitter 4 is converged by a cylindrical lens 11 to be incident to a four-split beam detector 12. The focal shift to the reflective surface of the lens 6 can be detected by the differential output of the detector 12.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical head for recording information on a recording medium or for reproducing information signals on a recording medium using a light beam emitted from a light source. The present invention relates to a device for inspecting the optical axis of a lens used in such applications.

Conventional technology In optical information recording and reproducing devices using optical discs, etc.,
It is necessary to focus the laser beam on the track to a diameter of 1 μm or less, and one of the factors that worsens this focused spot is the inclination of the optical axis of the objective lens. In other words, when the mounting reference surface of the actuator that holds the objective lens is parallel to the disk surface, and the laser beam is incident perpendicularly to the reference surface, the relative incidence on the lens is This causes a tilt of the light and a tilt of the disk, and the focal spot deteriorates due to the occurrence of aberration.

Therefore, in order to improve the recording and reproducing characteristics, it is important to reduce the inclination of the actuator mounting of the optical axis of the objective lens with respect to the reference plane.

FIG. 2 shows a plan view of the objective lens actuator, and FIG. 3 shows a sectional view of the objective lens actuator. 51 in Figures 2 and 3
is an objective lens, which is fitted and fixed to a lens holder 63 supported by elastic support members 52a and 52b. A tracking drive coil 64 is attached to the lens holder 53. A focus drive coil 55 is attached, and each tracking drive magnet unit 5
In combination with the 6° focus drive magnet unit 57, it can move in the tracking direction and focus direction. Further, by detecting the tracking error signal and the focus error signal and performing feedback control, it is possible to form a focused spot on the track that is stable against runout of the eccentric nine planes of the disk.

The elastic support member fixing member 58 is integrally molded with the elastic support member 52a, and is fixed to the housing 59 with screws 60a to 6od. The through hole provided in the elastic support member fixing member 58 has a larger screw diameter, and by moving the through hole, the optical axis of the objective lens 51 can be adjusted.

A conventional lens optical axis inspection method will be explained with reference to FIG. 61
62 is a tapered dummy lens that fits into the lens holder 53 and has a reflective surface on the bottom surface, and 62 is a reference base for fixing the actuator housing 59. The He-Ne laser light source 63 is adjusted so that its emitted light is perpendicularly incident on the reference stand 62.

Here, the elastic support member fixing member 58 is moved to change the inclination of the lens holder 53, and the tapered dummy lens 61 is moved.
Adjustments are made so that the reflected light from the reflecting surface returns to the emission hole of the He-Ne laser 63. Through the above procedure, the lens holder 53 is adjusted perpendicularly to the reference stand 62.

Problems to be Solved by the Invention However, in the above configuration, the perpendicularity of the tapered dummy lens 61 with respect to the reference table 62 is inspected and adjustments are made based on the inspection, and the optical axis of the objective lens 51 itself is cannot be inspected. Therefore, if there is any play in the fitting between the lens barrel of the objective lens 51 and the lens holder 53, and if there is a tilt between the optical axis of the objective lens 51 and the center axis of the lens barrel, there is a problem in that an error occurs in the optical axis inspection.

Means for Solving the Problems In order to solve the above problems, the lens optical axis inspection device of the present invention includes a light source that emits parallel light, a reference plane plate, and a reflection plate installed at the focal point of the lens to be inspected. It has a surface.

According to the above-mentioned configuration, the present invention generates interference fringes between the parallel light reflected from the reference flat plate and the light that is guided through the test lens, reflected by the condensing diameter reflecting surface, and parallelized again by the test lens. . When the lens under test is tilted at an angle that maximizes the performance of the lens, the distortion of the two fringes is minimized. Therefore, the optical axis of the lens can be inspected based on the distortion of the interference fringes.

Example Below, regarding a lens optical axis inspection device according to an example of the present invention,
This will be explained with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Reference numeral 1 denotes a light source section, which is composed of, for example, a semiconductor laser and a condensing lens, and emits parallel light. It is desirable that the light source has a wavelength that minimizes the aberrations of the lens to be tested, but a light source with a different wavelength may also be used. The parallel light passes through the first beam splitter 2 and is split into reflected light and transmitted light by the reference plane plate 3. The transmitted light is adjusted so that it is reflected by the second beam splitter 4 and enters the reference stand 5 perpendicularly. The light emitted perpendicularly from the reference stand 5 is the subject lens 6.
and forms an image on the reflecting surface 7. The reflective surface 7 is the reference stand 5
The test lens 6 is placed parallel to the
．． If it is designed to form an image through a 2H parallel glass plate, it is preferable to provide the equivalent with a reflective surface 7.

The light reflected from the reflecting surface 7 is further split into reflected light and transmitted light by a second beam splitter '4. The reflected light passes through the reference flat plate 3, is reflected by the first beam splitter 2, and enters the imaging device 9 via the light flux conversion lens 8. The light reflected from the reference flat plate 30 is similarly reflected by the first beam splitter 2 and enters the imaging device 9 via the light flux conversion lens 8.

This incident light interferes with the incident light to generate interference fringes, which can be observed on the display device 1o. In order to obtain interference fringes with high contrast, the amounts of the two incident lights need to be approximately the same. For example, when the transmittance of the test lens is set to 96, each reflectance is set to the reference plane plate 4 and the beam spring. 250%
1 reflective surface should be 20%.

The light transmitted through the second beam splitter 4 is focused by the cylindrical lens 11 and sent to the 4-split photodetector 7.
incident on . The differential output of the four-split photodetector 12 is a focus error signal based on the so-called astigmatism method, and can detect the focal shift of the focused spot of the test lens 6 with respect to the reflecting surface 7. Furthermore, if this signal is fed back to the actuator drive section via the focus servo circuit 13, autofocus can be achieved.

The interference fringes observed with the above configuration are equivalent to those obtained with a so-called Fizeau type interferometer.
The purpose is to observe the distortion of the wavefront after passing through the test lens with respect to the reference plane wave that is reflected. Currently tested lens 6
If the reference table 5 is tilted with respect to the reference stand 5, aberrations occur and the wavefront of the light transmitted through the test lens 6 is distorted, and the observed interference fringes are also distorted.

Therefore, the lens optical axis can be adjusted by moving the elastic support member fixing member in two directions so that the distortion of the interference fringes is minimized.

- In the above description, the astigmatism method was used as the focus error detection method for controlling the focal plane of the test lens to be on the reflective surface, but the Naifezi method, critical angle method, etc. may also be used.

Effects of the Invention As described above, in the present invention, by observing the distortion of the wavefront transmitted through the test lens using interference fringes, it is possible to directly measure the inclination of the optical axis of the test lens. Therefore, it is possible to accurately measure and adjust the inclination of the lens optical axis without being affected by the fitting play between the lens barrel and the lens holder or the inclination between the lens optical axis and the lens barrel center axis, as in the conventional example.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a lens optical axis inspection device according to an embodiment of the present invention, Figs. 2 and 3 are a plan view and a sectional view of an actuator on which a lens to be inspected is installed, and Fig. 4 is a diagram of a conventional lens. FIG. 2 is a configuration diagram of an optical axis inspection device. 1...Light source part, 3...Reference plane plate, 6
...Test lens, completed...Reflective surface, 1゛1...Cylindrical lens, 12...
・4-split photodetector. 1 Light source section 2.4 - Beam splitter 3 Reference plane plate 7 Reflection surface 9 - Imaging device 11 / Lintrical lens I2...4-split photodetector Fig. 2 Fig. 3 Fig. 2b

Claims (1)

[Claims] A light source, a reference plane plate that reflects a part of the collimated light beam emitted from the light source, a reflecting surface installed at the focal plane of the emitted light beam by the test lens, and a light reflected from this reflecting surface and the reference flat plate. It has an imaging device for observing interference fringes caused by light reflected from the face plate, and a detection means for detecting a focal plane of the lens to be tested, and detects an optical axis tilt of the lens to be tested based on the interference fringes. Lens optical axis inspection device.