JPS6074131A - Optical head - Google Patents

Abstract

PURPOSE:To make an optical head small-sized and inexpensive by providing a spot shape converting means for verying the shape of a spot formed on an information storage medium, on an optical path of an optical beam reaching the information storage medium from a light source. CONSTITUTION:When recording and reproducing are executed, a slit 27 for converting a spot shape is not interposed in an optical path 28. When executing erasion, a pair of slit plates 27b, 27b having a deep groove 27a move along the X direction from both sides of the optical path 28, and the slit 27 is interposed in the optical parh 28. As a result, immediately before an objective lens 29, a spot shape 40 on a far field surface to a recording layer 31 becomes long in the X direction and short in the Y direction, and the spot shape on the recording layer 31 becomes an elliptical shape having a long axis in the Y direction and a short axis in the X direction. In accordance with this variation, a spot shape 38 is also varied, but as for said spot shape 40, the size is varied only in the Y direc tion, therefore, the size veriation of the spot does not occur in the X' direction of a photodetector 33, and accordingly, when executing erasion, too, a track shift can be detected stably.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to recording information on an information storage medium using focused light.
The present invention relates to an optical head capable of reproducing or erasing recorded contents as the case may be.

[Technical background of the invention and its problems]

In addition to using thermoplastics and magneto-optical effects as erasable information storage media, there are other methods for recording and reproducing information that utilize the differences in optical properties that exist between crystalline and amorphous states. . In this case, an amorphous state is created by rapid heating and rapid cooling, and a crystalline state is created by slow heating and slow cooling.

By the way, there is a conventional optical head that uses this method as shown in FIG. This optical head performs recording, reproduction and erasing on an information storage medium 1 using two beams 2 and 3 having different condensed spot shapes.

However, in this case, since two light sources 4 and 5 are required, the optical system becomes complicated, the overall size increases, and the cost also increases.

In FIG. 1, 6 is a recording and reproducing beam spot, 7 is an erasing beam spot, 8 is a polarizing beam splitter, and 9 is a beam spot for erasing.
10 is a filter, 1o is a light receiving element, and 11... are lenses.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its purpose is to be extremely compact and low in cost.
Moreover, the structure is to provide rad to a simple optical system fj+j.

[Summary of the invention]

In order to achieve the above object, the present invention irradiates a light beam onto an information storage medium and connects the light beam emitted from the light source to an optical device for recording, reproducing or erasing information. An objective lens that focuses light toward the information storage medium, and a stripe shape that is interposed on the optical path of the light beam from the light source to the information storage medium and that changes the shape of a spot formed on the information storage medium. The feature is that it is equipped with a conversion means.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. 21 in FIGS. 2 and 3 is a semiconductor laser as a light source, and a laser beam 22 emitted from this semiconductor laser 2I is transmitted through a collimator lens 2.
3, the parallel light passes through the triangular prism 24, where it is corrected into an ellipse, and the intensity distribution near the center is changed to 11. is close to a concentric distribution. Further, the laser beam 22 travels straight through the polarized beam mirror 25 and passes through the λ/4 plate 26, after which the laser beam 22 becomes circularly polarized light. When recording and reproducing information, the slit 27 for converting the spot shape is not interposed in the optical path 28 of the laser beam 22 as shown in FIG.
It has no effect on 8. Therefore, the laser beam 22 is irradiated with the entire aperture of the objective lens 29 or a part of the aperture extending beyond the information storage medium 30.
On the recording layer or light reflection layer 31, the light is focused as a small, almost circular spot on the non-door. During recording, rapid heating and cooling by this spot creates an amorphous state on the information storage medium 30. Information storage medium 30
It is reflected by the recording layer or light reflecting layer 31 of the objective lens 29.
The laser beam 22 that has passed through the λ/4 plate 2 and the metal plate 6 becomes a linearly polarized light whose vibration plane is rotated by 90 degrees, so it is reflected by the polarized beam sinter 25 and proceeds to the detection system. In the detection system, the laser beam 22 is divided into two directions by a half prism 32, one of which is irradiated onto a first photodetector 33, where track deviation detection and information reading are performed. The other light passes through a light extraction member 34 such as a knife edge and a projection lens 35 in order and is irradiated onto a second photodetector 36, where out-of-focus detection is performed.

By the way, when erasing information, as shown in FIG. 3, a pair of slots and plates 27b and 27b having deep grooves 27a cut from opposite sides move along the X direction from both sides of the optical path 28. Optical path 2 of laser beam 22 in this 1
This means that a slit 27 is interposed in the slit 8 to extract a part of the light and let it pass through. As a result, the spot shape 40 on the far field surface of the recording layer 31 of the information storage medium 30 immediately before the objective lens 29 changes into a rectangle that is long in the X direction and short in the Y direction.

Therefore, the spot shape on the recording layer 31 of the information storage medium 30 is an ellipse with a long axis in the Y direction along the direction of the tracking guide 37 and a short axis in the X direction. A crystalline state is created on the multi-information storage medium 30 by slow heating and slow cooling using this spot.

Accordingly, the spot shape 38 on the first photodetector 33 also changes in accordance with the above change. However, the spot shape 40 on the far field surface is parallel to the direction of the tracking guide 37 of the information storage medium 30 (Y direction).
Therefore, the dimension of the spot does not change in the X' direction where the photodetector 33 detects the track deviation, but the dimension changes only in the Y' direction, which is perpendicular to the X' direction. Therefore, track deviation detection can be performed stably during erasing as well as during recording and reproducing.

Furthermore, in the out-of-focus detection system, the following phenomenon occurs when the spot shape on the far field surface changes during erasing.

In addition, in FIGS. 2 and 3, a focal point t"=retrieval detection method is adopted in which a light extraction member 34 such as a knife nip is provided in the middle of the optical path 28 of the laser beam 22, but this method is not limited to this method. The content will be explained as being applicable to a conventional detection method.
A second photodetector 36 having a photosensitive area consisting of two blocks is placed at or near the imaging position for the image, and defocus detection is performed using the difference in the amount of laser light irradiated to each block. We will deal with common problems that arise with detection methods. Here, "the photosensitive area consists of two blocks" includes, for example, a case where the second photodetector 36 has four photodetection cells and two photodetection cells are grouped together and used as two blocks. 0 ■ The spot shape 39 on the second photodetector 36 changes. In this state of change, the direction in which the spot size changes on the far feel surface 2 (Y direction) is projected onto the photodetector 36, and a size change occurs in the saw direction (Y" direction). Third
In the case of the optical system shown in the figure, the spot becomes long.

■ The ratio of the spot size on the second photodetector 36 to the focusing lid changes in the Y" direction. When comparing the case shown in FIG. 2 with the case shown in FIG. Although the negative change in the "Y" direction remains the same, the amount of change in the Y direction is much smaller in FIG.

Therefore, if two blocks for light detection are arranged along the Y direction, the optical focus detection sensitivity will change between recording, playback and erasing, or the focus correction position will shift. To prevent this from occurring, an unstable state of Two blocks for performing brush detection are arranged. This makes it possible to perform out-of-focus detection stably even when erasing, just as when recording or writing.

In addition, regarding the 5 m 7' slits in which the slits 27 are arranged, the spot size of the laser beam 22 after passing through the slits 27 becomes slightly larger as the distance increases due to the influence of light diffraction, so It is better to place it near the lens 29. In FIGS. 2 and 3, it is inserted between the polarizing beam sgritter 25 and the λ/4 plate 26, but the λ/4 plate 26 is placed in front of the objective lens 29.
Immediately after step 6, the slit 27 may be made scratch resistant.

Also, as shown in FIGS. 2 and 3, the slit 27 is connected to the optical path 2.
If the beam 22 is present in the middle of the recording layer 31 of the information storage medium 30, the efficiency of the beam 22 reaching the recording layer 3 of the information storage medium 30 during erasing will be significantly reduced.
Heat slowly, return to polycrystalline state by slow cooling, 1;
When erasing information, it is sufficient to irradiate a certain location on L (recording layer 3) of the information storage medium 30 with an appropriate amount of light for a long time. Therefore, in the conventional optical system shown in FIG. 1, erasing is performed by enlarging the erasing beam spot size 7 by ten times in the track direction without changing the rotational speed of the information storage medium 1. On the other hand, in the optical system of the present invention, the tracking guide 3 is placed on the recording layer 3 of the information storage medium 30 during erasing.
The information storage medium 3 is stretched only 2 to 4 times in 7 directions.
0 rotation speed is slowed down to lengthen the exposure time. By doing this, in the conventional optical system shown in the Igi diagram, many bits of information are erased at once, but with the present invention, it is possible to erase only 1 to 3 bits of information.

Further, the spot shape 38 on the first and second photodetectors 33 and 36 is added at the time of switching between recording, reproduction and erasing.
39 is the detection direction (X/direction).

If there is even a slight asymmetry with respect to the
Alternatively, in order to falsely detect a track deviation, the K symmetry in the direction perpendicular to the track direction (X direction in the fourth factor in Figure 83) on the far field plane with respect to the focused state on the information storage medium 30 at the time of focus. This is done so that the spot shape is changed while maintaining the . That is, Figure 2,
As shown in FIG. 3, two slit plates 27b.

In addition to changing the spot shape by closing and opening the slit 27b, the slit 27 is placed on the optical path 28, and the spot shape is changed. The spot shape can also be changed by interposing a cyslit 27 as shown in the figure. That is, in FIG. 4, a shallow recess 27c'f is formed on the opposite side, and a pair of shoulder slit plates 27d and 27d are moved along the Y direction, and in FIG. 5, a plurality of slit holes 27 with different widths are moved.
A pickpocket with e..., move the top plate 27f along the Y direction -C
When the width becomes narrower in FIG. 6, the slit disk 27h having the line groove 27g is rotated. In addition, Fig. 4 (a
), FIG. 5(a), it is possible to stably detect out-of-focus and out-of-track detection even at the switching time υ between reproduction and erasing.

According to the above configuration, since only one light source is required, recording, reproduction, and erasing can be performed using a very simple optical system.

Additionally, the overall size of the optical head can be made much smaller. Furthermore, even though erasing is possible, the cost of the optical head is almost the same as that of conventional recording and reproducing heads (cost is low).

In addition, the optical head can continue to perform stable focus correction and track deviation correction even during recording, playback, erasing, and switching.
Regarding track deviation correction, the same circuit can be used for each case (there is no need to change the circuit depending on each case)0 [Effects of the Invention] As explained above, according to the present invention, For example, an optical head that irradiates a light beam onto an information storage medium to record, reproduce, or erase information includes a light source and an objective lens that focuses the light beam emitted from the light source toward the information storage medium. and a spot shape converting means that is interposed on the optical path of the light beam from the light source to the information storage medium specified in E and changes the shape of the spot formed on the information storage medium. It always has excellent effects such as low cost and easy configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a conventional example, FIGS. 2 and 3 show an embodiment of the present invention, FIG.・Light source (semiconductor laser), 27...slit, 29...objective lens,
30... Information storage medium.

Claims (7)

[Claims] (1) In a device that records, reproduces, or erases information by irradiating a light beam onto an information storage medium, there is a light source and an objective that focuses the light beam emitted from the light source toward the information storage medium. It is characterized by comprising a lens, and a spot shape converting means that is interposed on the optical path of a light beam from the light source to the information storage medium and changes the shape of a spot formed on the information storage medium. optical head. (2) The optical head according to claim 1, wherein the shape of the spot is changed when recording/reproducing information and when erasing information. (3) The optical head according to claim 1 or 2, wherein the spot shape converting means is a slit. (4) Pickpocketing 1. 1. Set the self f value to in' *t+ of the objective lens. The optical head according to claim 3, characterized in that: (5) Claim 3 or 4, characterized in that the slit changes the spot shape on the far field surface in a direction parallel to the track direction of the information storage medium.
Optical head described in section. (6) A patent characterized in that the spot shape is changed while maintaining symmetry in the direction perpendicular to the track direction on the far-field surface with respect to the focused state on the information storage medium at the time of focusing. An optical head according to any one of claims 3 to 5. (7) The optical head according to any one of claims 1 to 6, characterized in that when erasing information, the information storage medium is scanned at a speed υ slower than when recording.