JP2576641B2 - Optical head device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for recording and reproducing a so-called rewritable (E-DRAW) magneto-optical disk.

[Conventional technology]

There are various types of conventional optical head devices, one of which uses a hologram element. The optical head device having this configuration can detect a focus error signal, a tracking error signal, and a recording signal with a simple configuration without using a beam splitter or a lens required for a conventional head. For example, as shown in FIG. 2, a semiconductor laser 1 serving as a light source and a radiation 2
Lens 3 for collimating the light, a converging lens 4 for converging the light of the semiconductor laser on an optical disk 8 as a recording medium, and a six-segment photodetector 7 for returning light from the optical disk.
And a hologram element 5 that leads to the hologram element.

In this optical head device, the undiffracted light, that is, the transmitted light of the hologram element 5 is used for the light going from the semiconductor laser 1 to the optical disk 8, and the diffracted light is used for the return light from the optical disk. The signal and the recording signal are detected.

[Problems to be solved by the invention]

Magneto-optical disks differ from recording systems for recording signals with read-only compact disks and video disks, and utilize the fact that the plane of polarization of reflected light is rotated by the Kerr effect when linearly polarized light enters the disk. Therefore, the magneto-optical disk cannot be reproduced by the optical head device using the hologram element described in the related art.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small and lightweight magneto-optical disk head device that solves the above-mentioned drawbacks.

[Means for solving the problem]

The present invention provides a light source, an imaging lens system for focusing an image of the light source on a recording medium, a hologram element for diffracting and separating return light from the recording medium out of the optical axis of the imaging lens system, and An optical head device comprising: a quarter-wave plate disposed between a medium and the hologram element; and a photodetector that receives diffracted light separated off the optical axis, The element is composed of at least two hologram regions symmetrically arranged with respect to a division line perpendicular to the track direction on the recording medium, and detects a recording signal from a difference between diffracted light from the two hologram regions. It is characterized by the following.

[Action]

 The operation and principle of the present invention are as follows.

The optical head device of the present invention employs a method using circularly polarized light or a phase difference as a method for reading a recording signal of a magneto-optical disk. Whereas the conventional signal reading method for a magneto-optical disk utilizes the fact that the plane of polarization of reflected light is rotated by the Kerr effect when linearly polarized light enters the disk, this method uses circularly polarized light. This method utilizes the fact that the phase of the reflected light changes due to the Kerr effect according to whether the direction of magnetization of the disk recording medium is upward, downward, or downward when incident. Such a phase difference is
This means that the difference in the magnetization direction of the recording medium is equivalent to the difference in the optical path length, and even if it is considered that the pit portion where the magnetization direction is reversed is a depression of a certain depth Good. At the boundary of the pits in the track direction, the light intensity distribution becomes unbalanced in the track direction due to the interference between the reflected light from the upper portion of the pit and the reflected light from the lower portion of the pit. Therefore, in this method, the reflected light that is unbalanced in the track direction is received by a two-segment detector in which each photodetector is arranged in the track direction, and the recording signal is obtained by taking the difference between the outputs of the two photodetectors. Can be detected. A signal reading method using the phase difference of the circularly polarized light is described in the Journal of the Japan Society of Applied Magnetics (p.215-218) published in 1988, VOL.12, No.2.
JCLehureau et al. Describe in detail the title of "Application of Circularly Polarized Light to Magneto-optical Reading System".

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a view showing a first embodiment of the present invention, and the same elements as those of the conventional optical head device of FIG. 2 are denoted by the same reference numerals. This optical head device includes a semiconductor laser 1 as a light source and an optical disk 8 as a recording medium for storing an image of the semiconductor laser.
An imaging lens system including a collimating lens 3 and a converging lens 4 that are narrowed upward, a hologram element 5 for diffracting and separating return light from a recording medium out of the optical axis of the imaging lens system, a collimating lens 3 and a converging lens 4, And a six-segment photodetector 7 that receives the diffracted light separated off the optical axis by the hologram element 5.

As shown in FIG. 3, the hologram element 5 includes four hologram regions having different diffraction directions. That is, the two first and second hologram areas 36, 3 symmetric with respect to the division line 44 perpendicular to the track direction on the recording medium.
7 and two third and fourth hologram regions 38 and 39 symmetrically arranged on the dividing line 44 with respect to the optical axis. The recording signal is transmitted to the first and second hologram areas 36 and 37.
The focus error signal is detected from the diffracted light from the first and second hologram areas 36 and 37. The tracking error signal is detected based on the difference between the diffracted light from the third and fourth hologram areas 38 and 39.

FIG. 4 simultaneously shows the λ / 4 plate 6, the converging lens 4, and the optical disk 8 via an omission line 25 in order to show the directional relationship between the divided areas in the hologram element and the tracks.

In the optical head device having the above configuration, the semiconductor laser 1
The radiated light 2 which is linearly polarized light is transmitted through the hologram element 5 without being diffracted, converted into collimated light 10 by the collimating lens 3, and converted into circularly polarized light by the λ / 4 plate 6. Then, the light is converged on the optical disk 8 by the converging lens 4. The reflected light from the optical disk 8 passes through the converging lens 4, the λ / 4 plate 6, and the collimating lens 3 in the reverse path. In the λ / 4 plate 6, the circularly polarized light is returned to the linearly polarized light again, but the light intensity distribution does not change. Then, this return light is diffracted by the hologram element 5 and enters the six-divided photodetector 7.

Of the return light from the optical disk 8, the light incident on the first hologram region 36 and the second hologram region 37 symmetrically arranged with respect to the division line 44 perpendicular to the track direction 45 The light converges to points 40 and 41 on the dividing lines of the photodetectors 31, 32, 33, and 34. At the same time, the light incident on the third hologram region 38 and the fourth hologram region 39 symmetrically arranged on the division line 44 with respect to the optical axis is also reflected on the light detection elements 29 and 30 of the six-division photodetector. It converges to 43 and 42. The first hologram area 36 has a hologram pattern corresponding to an interference fringe of a spherical wave emitted and diverged from the semiconductor laser 1 and a spherical wave diverged from a convergence point 40 of the diffracted light. Other first
Similarly, the second and third and fourth hologram regions 37, 38 and 39 also have convergence points of the diverging spherical waves from the semiconductor laser 1 and the respective diffracted lights.
It has hologram patterns corresponding to interference fringes with spherical waves diverging from 41, 42, 43.

FIG. 5 is a diagram for explaining the state of the diffracted light on the six-segment photodetector 7. FIG. 5 (a) is a view showing a focused state in which a light beam is converged on the optical disk 8, and FIGS. 5 (b) and (c) show that the disk surface is displaced and the convergent lens 4 is displaced.
There are cases where the user moves away from the vehicle and cases where the user approaches the vehicle. If the outputs of the four photodetectors 31, 32, 33, 34 in the six-segment photodetector 7 are V (31), V (32), V (33), V (34), the focus error signal is (V (31) + V (34))-(V (32) + V (3
3)).

On the other hand, the tracking error signal is detected by utilizing the fact that the light intensity distribution of the return light becomes unbalanced when the focused spot on the optical disc 8 deviates from the center of the track. That is, when a tracking error occurs, a difference occurs between the amounts of light incident on the third hologram region 38 and the fourth hologram region 39. The outputs of the two photodetectors 30 and 29 where the diffracted lights from the respective regions 38 and 39 converge and enter are V (30) and V
Assuming (29), the tracking error signal is V (29) −V
Obtained from (30).

As mentioned in the section on the detection of recorded signals,
A reading method using circularly polarized light is used. Optical disk 8
The light intensity distribution of the circularly polarized reflected light from the hologram is unbalanced in the track direction at the boundary due to the effect of the pit depression, so that the first hologram region 36 and the second hologram arranged along the track direction The recording signal can be detected from the difference in the amount of light incident on the area 37. That is, the outputs of the four photodetectors 31, 32, 33, and 34 shown in FIG. 5 where the diffracted lights from the respective regions 36 and 37 converge and enter are represented by V (3
1), V (32), V (33), V (34), the playback signal is V
(31) + V (33)-(V (32) + V (34)).

In the first embodiment described above, the collimating lens and the converging lens 4 are used as the imaging lens system for focusing the image of the semiconductor laser on the recording medium. However, the present invention is not limited to this.

FIG. 5 shows a second embodiment of the present invention, in which the collimating lens 3 and the converging lens 4 of the first embodiment are replaced by a single imaging lens 9.

〔The invention's effect〕

In the optical head device using the hologram element of the present invention,
By simply inserting a λ / 4 plate into an optical head device using a conventional hologram element, it is possible to generate a signal of a magneto-optical disk from which a signal cannot be read.

Also, while a conventional optical head device for a magneto-optical disk requires a large number of optical components, the optical head device of the present invention uses a hologram element, so that a small and lightweight optical head device can be provided. It is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a basic configuration diagram of an optical head device using a conventional hologram element, and FIG. FIG. 4 is a partial perspective view of the optical head device of FIG. 1, FIG. 5 is a diagram for explaining a state of diffracted light on a six-segmented photodetector, and FIG. It is a figure showing a 2nd example. DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Radiation beam 3 ... Collimating lens 4 ... Convergent lens 5 ... Hologram element 6 ... λ / 4 plate 7 ... 6 division | segmentation photodetector 8 ... Optical disk 9 ... Imaging lens 10 Collimated light 29, 30, 31, 32, 33, 34 Photodetector 36, 37, 38, 39 Grid area 40, 41, 42, 43 Convergent point 44 Dividing line 45 … Track direction

Claims (1)

(57) [Claims] A light source, an imaging lens system for focusing an image of the light source on a recording medium, a hologram element for diffracting and separating return light from the recording medium out of the optical axis of the imaging lens system, An optical head device including a quarter-wave plate disposed between a recording medium and the hologram element, and a photodetector that receives diffracted light separated off the optical axis, The hologram element is symmetrically arranged at least with respect to a division line perpendicular to the track direction on the recording medium.
And a hologram area.
An optical head device, wherein the detection is performed based on a difference between diffracted lights from two hologram regions.