JPS63268131A - Detection of light axis tilt of objective lens of light pick-up - Google Patents

Abstract

PURPOSE:To effectively detect the light axis tilt of a light pick-up objective lens by the deviation of the image forming point of a measuring light source due to one curved surface of the objective lens and the measuring light source position. CONSTITUTION:When a first lens surface R1, namely, a light axis tilt angle, which is an inclination angle to a reference light axis NX of a light axis AX of an objective lens 14, is theta, the distance of a measuring light source Q and an image forming point Q1 due to the lens surface R1 is given by 2rtheta with the curvature radius of the lens surface R1 as (r). Consequently, by the deviation of the image forming point Q1 of the measuring light source Q and the measur ing light source position, the tilt to the reference light axis of the light axis of the objective lens 14 can be detected. Even when the tilt angle theta itself is a minute quantity of 10' or less, the radius of curvature (r) is a quantity on the order of several mm, the deviation of the measuring light source position is made much larger and the light axis tilt of a minute angle can be effectively detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for detecting optical axis inclination of an objective lens of an optical pickup.

(Prior Art) An optical pickup is well known as a device for writing information onto an optical disk or reading information recorded on an optical disk in an optical disk system.

In an optical pickup, it is important that the optical axis of the objective lens is not tilted. In FIG. 6 (II),
Reference numeral 100 indicates an optical disk, and reference numeral 200 indicates an objective lens of the optical pickup. This figure shows the objective lens 20
0 indicates that the light beam is correctly incident on the optical disc 100. At this time, the light intensity distribution on the recording surface of the optical disc has a symmetrical mountain shape as shown in Fig. 6 (III), and is focused in a spot shape on the No. 5 track T as shown in Fig. 6 (I). Reads and writes information. 6th
In the figure, the optical axis of the objective lens 200 is exactly perpendicular to the recording surface.

As shown in FIG. 7 (II), the optical axis A of the objective lens 200
When X is tilted with respect to the recording surface, the image plane IN of the objective lens becomes
Since it is tilted with respect to the recording surface, coma aberration occurs and the light intensity distribution on the recording surface becomes asymmetrical as shown in Figure 7 (III), and the spot shape on the recording surface is as shown in Figure 7 (■). Become a kimono.

The arrangement pitch of the tracks T is generally about 1.6 μm, and the spot diameter of the focused light is about 1 μm under normal conditions. Therefore, the gap between adjacent tracks is small, and when coma aberration as shown in FIG. 7 occurs, crosstalk occurs when information from adjacent tracks is read.

Alternatively, if asymmetry in the light intensity distribution occurs in the track direction, a reading failure called jitter occurs. The tolerance range for the tilt of the objective lens optical axis with respect to the recording surface is ±10'
Within

Therefore, it is necessary to strictly check the optical axis tilt of the objective lens.

Conventionally, this check was performed by observing the spot condition through a transparent substrate that was placed with high precision as a reference, and when the spot shape or intensity distribution was asymmetric.

The inclination of the objective lens or the actuator holding the objective lens was adjusted in response to the optical axis tilt.

However, when the angle of inclination of the optical axis is approximately ±10', it is difficult to identify asymmetry in the spot state.

It was difficult to adjust the optical axis tilt more accurately.

(Objective) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a novel optical axis tilting system that can detect optical axis tilting of an objective lens of an optical pickup with extremely high precision. The objective is to provide a detection method.

(composition) The present invention will be explained below.

The present invention is a method for detecting optical axis tilt of an objective lens of an optical pickup. This method has the following features.

That is, the light beam from the light source of the optical pickup is condensed by the objective lens of the optical pickup, and a straight line passing through the condensing point and parallel to the reference optical axis and the R surface of one of the curved surfaces of the objective lens intersect separately. The light beam from the light source is focused and used as a measurement light source.

Inclination of the objective lens optical axis with respect to the reference optical axis is detected based on the deviation between the imaging point of the measurement light source due to the curved surface and the measurement light source position.

Here, the reference optical axis refers to the proper, ie, designed, optical axis of the objective lens. Further, the R surface is a plane perpendicular to the reference optical axis, on which the center of curvature of the curved surface is located.

Since the measurement light source is on the R plane, the image of the measurement light source by the curved surface is also formed on the R plane. If the optical axis of the objective lens is not tilted, the position of the measurement light source and the position of its image point coincide with each other.

Therefore, the tilt of the optical axis of the objective lens can be detected with high accuracy due to the deviation of the imaging point of the measurement light source from the measurement light source position due to the curved surface.

(Example) Hereinafter, a specific example will be described with reference to the drawings.

In FIG. 1, reference numeral 10 indicates an optical pickup. A light beam from a semiconductor laser 11 serving as a light source is collimated by a coupling lens 12.

The light enters the objective lens 14 via the polarized beam splitter 13, 174 and the wavelength plate 15.

The optical pickup 10 is arranged with the reference optical axis of the objective lens parallel to the Z direction. Therefore, the parallel light flux that enters the objective lens 14 is parallel to the Z direction.

Now, a microscope is installed above the optical pickup 10 in the figure.

The main parts of the microscope include a He-Ne laser 20 as a light source, a beam expander 21. It has a deflection prism 22, a reticle 23, a beam splitter 24, an objective lens 25, a relay lens 26, a camera 27, and a display 28. The optical axis of the objective lens 25 of the microscope is parallel to the Z direction.

Although the microscope and the optical pickup 10 are relatively movable in the Z direction, the Y direction, and the X direction perpendicular to the drawing, in this embodiment, the optical pickup 10 is fixedly supported, and the optical pickup 10 In contrast, the microscope is assumed to be movable in the three directions mentioned above.

Further, the curved surface indicated by the symbol R1 in FIG. 1 is the lens surface of the objective lens 14, and is a concave surface facing toward the objective lens 25 of the microscope. An example will be described in which the optical axis tilt of the objective lens 14 is detected using this lens surface R1 as a curved surface.

First, while the semiconductor laser 11 of the optical pickup 10 is turned off, the He-Ne laser 20, which is another light source, is turned on. The emitted laser beam irradiates a reticle 23 via a beam expander 21 and a deflection prism 22. The light beam from the reticle 23 enters the objective lens 25 via the beam splitter 24.
At this time, the position of the microscope in the Z direction is adjusted so that the focal point of the focused light by the objective lens 25 is located on the lens surface R1 of the objective lens 14. FIG. 1 shows exactly this situation.

The reflected light from the lens surface R1 passes through the objective lens 25, beam splitter 24, and relay lens 26 to the camera 2.
78 and forms a crosshair image of the reticle 23 on the light receiving surface of the camera 27. The camera 27 is an area sensor, and in this embodiment a COD camera is used. The crosshair image is displayed on the lobby play 28. In this state, the position of the crosshair image is aligned with the center of the reference (broken cross) fixedly set on the display 28, as shown in FIG.

In this way, the standard is determined.

Next, the He-Ne laser 20 is turned off, and the semiconductor laser 11 of the optical pickup 10 is turned on instead.

Then, while moving the microscope upward in the Z direction, the display 28 is observed. Due to this movement, objective lens 1
4.25, the spot image of the focused light appears on the display 28 when the focusing position of the focused light by the objective lens 14 coincides with the imaging plane of the objective lens 25 of the microscope.

Next, the microscope is moved in the X and Y directions so that the image of the spot is located at the center of the reference fixedly set on the display. FIG. 3 ([I) shows this state. Symbol SP indicates the image of the spot. When this state is realized, the focal point P of the focused light by the objective lens 14 of the optical pickup 10 is as shown in FIG.
It is located on the imaging plane S of the objective lens 25 of the microscope and on the optical axis of the objective lens 25.

From this state, the microscope is further moved upward in the Z direction in FIG. FIG. 4(I) shows this state. Reference numeral S1 indicates the R surface of the lens surface R1 of the objective lens 14. These two surfaces S1 coincide with the imaging surface S.

In FIG. 4(1), the symbol Q is the spot position of the light beam from the He-Ne laser 20, which is a separate light source, and which is focused by the objective lens 25, and is the measurement light source.

The position of this measurement light source Q is on the R plane S1, and this position can also be expressed as follows.

The state shown in FIG. 4(I) was achieved by moving the microscope upward in the Z direction from the state shown in FIG. state.

However, the Z direction is parallel to the reference optical axis placed on the optical pickup 10, and the state shown in FIG.
Since the position of the light condensing point according to 4 coincides with the image forming position of the objective lens 25, the position of the measurement light source Q in FIG. A straight line parallel to the optical axis and the lens surface RIR of the objective lens 14
This is the intersection with the surface S1.

The light from the measurement light source Q enters the lens surface R1 while diverging, and when reflected, forms an image Q1 of the measurement light source on the R surface sl.

This imaging point Q1 is displayed as a spot image Sq on the display 28 of the microscope as shown in FIG. 4 (II).
It will be noticed.

Here, referring to FIG. 5, if the inclination angle of the optical axis AX of the objective lens 14 relative to the reference optical axis Nχ, that is, the inclination angle of the optical axis is θ, then the measurement light source Q and the optical axis AX of the objective lens 14 are The distance from the imaging point Q1 due to R1 is the lens surface R1
It is given by 2rθ, where r is the radius of curvature of .

Therefore, if there is no tilt in the optical axis of the objective lens 14, θ=0, so the position of the measurement light source Q and its imaging point Ql
The spot image on the display 28 matches the position of
The position of Sq is the reference position, that is, the center of the broken cross line.

Therefore, the tilt of the optical axis of the objective lens 14 with respect to the reference optical axis can be detected based on the deviation between the imaging point Q1 of the measurement light source Q and the measurement light source position.

Even if the inclination angle θ itself is a minute amount of 10' or less, the radius of curvature r is on the order of several mm, so the deviation between the imaging point Q1 of the measurement light source Q and the measurement light source position is quite large. It is possible to effectively detect optical axis tilt at minute angles. Further, in the described embodiment, the above-mentioned deviation can be further magnified and observed using a microscope, so that more accurate detection is possible. In addition,
The inclination angle θ is the spot image Sq (
If the distance between the reference position (see Figure 4 (H)) is d and the magnification of the microscope is m, then d = 2mrθ, so using this relationship, we know that θ = d / (2mr). be able to.

Also, while observing the state shown in FIG. 4 (II) on the display 28, tilt the objective lens 14 or the aperture that holds it to bring the imaging point Sq to the reference position, that is, the intersection of the broken cross lines. objective lens 14 to position
Optical axis tilt can be corrected by adjusting the attitude of the lens.

Note that although the optical axis of the objective lens 14 may be deviated from parallel to the reference optical axis, such a parallel deviation of the optical axis does not affect the detection of the present invention. This is because, in the case of parallel misalignment of the optical axes, the focal point of the objective lens 14 is a point on the optical axis, and therefore the position of the measurement light source is also a point on the optical axis, and the measurement light source and its imaging point are This is because they match each other in position.

(Effects) As described above, according to the present invention, a novel method for detecting optical axis tilt of an objective lens in an optical pickup can be provided.

Since this method is configured as described above, it is possible to accurately detect the optical axis inclination of the objective lens of the optical pickup. That is, since the curved R surface of the objective lens has an inclination of only 2 to 3' in the worst case, by using this surface as a reference, highly accurate detection is possible.

In the embodiment, the lens surface of the objective lens J4 is used, but other curved surfaces may be used, and it is also possible to use a convex surface instead of a concave surface as in the embodiment.

However, when using a lens surface other than the lens surface, it is necessary to determine the R surface based on the optical distance including the lens component, and considering the ease of setting the R surface, it is better to use the lens surface. is good.

[Brief explanation of the drawing]

FIG. 11 is a diagram for explaining one embodiment of the present invention, FIGS. 2 to 5 are diagrams for explaining detection of optical axis tilt in the above embodiment, and FIGS. 6 and 7 FIG. 2 is a diagram for explaining the present invention in detail. 1431, objective lens of optical pickup, P06. Focus point by objective lens, Qll, measurement light source, Sl, . R plane, Ql, , , imaging point U7 Illusion of σ b7 Ku

Claims (1)

[Scope of Claims] A straight line that passes through a convergence point where the light beam from the light source of the optical pickup is condensed by the objective lens of the optical pickup and is parallel to the reference optical axis, and an R surface of one curved surface of the objective lens. A light beam from another light source is focused at the intersection point to serve as a measurement light source, and due to the deviation between the imaging point of the measurement light source by the curved surface and the measurement light source position, the objective lens optical axis is tilted with respect to the reference optical axis. A method for detecting optical axis inclination of an objective lens of an optical pickup.