JPS6212936A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain recording immediately after deleting an information with one semiconductor laser by separating one beam into two beams that cross orthogonally each other by using a polarizing beam splitter to use said two beams as one for deletion and the other one for recording/reproduction. CONSTITUTION:The beam reflecting from the polarizing beam splitter 4 is beam-shaped by a mirror 17, a convex column lens 18, a concave column lens 19, and a mirror 20 to become of an elliptical section whose diameter in the direction parallel with the paper surface is shorter. This beam is made incident on the splitter 8 but 100% reflects because splitter 8 is of S-polarization. The beam is condensed by an objective lens 9, and irradiated on the track 11 of a disc 10 forming a deletion spot 21 of elliptical shape and delets an already recorded bit 22. Meanwhile, the beam reflecting from the disc 10 is made incident on the splitter 8 after transmitting through the objective lens 9, but is reflected because of the splitter's S-polarization, and accordingly does not enter an optical detector 16.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a recording/reproducing/erasing device for a phase change type reversible optical disk, which is an information recording medium, and is particularly suitable for recording information immediately after erasing it. Regarding optical systems.

[Background of the invention]

First, the principles of recording, erasing and reproducing a phase change reversible optical disc will be briefly explained.

A phase-change recording material changes from a crystalline state to an amorphous state by rapidly heating it above its melting point and then rapidly cooling it. As a result, the reflectance of light decreases, and the information signal is recorded in shading. On the other hand, by irradiating the material with a weak laser beam for a long time to gradually heat it above the crystallization temperature and slowly cool it, it returns to its original crystalline state and the information signal is erased. Reproduction is performed by emitting a weaker laser beam below the crystallization temperature and detecting changes in the amount of reflected light! Now.

The temperature T is the irradiation light puff density P' of the laser beam
It is thought that it is determined only by On the other hand, the heating time t is
This is considered to be approximately equal to the laser beam irradiation time t.

The irradiation time t is the tangential linear velocity V of the disk.
and the length t of the irradiated light in the tanzene direction, '-L/v-(1). In erasing, the time required for crystallization t11. Since the irradiation time t is required for During recording and reproduction, an O information signal is recorded using a minute circular beam, and the portions where the reflectance chi has decreased are called recording pits, and the other portions are called lands. now,
For simplicity, let the recording pit length and land length be equal to d. Since the minimum value of the recording pit length d is equal to Lf for the circular beam diameter, the maximum frequency of the recorded information signal 'm1Z
X is f # 7/'-/(2D)
(3) ffltL! It is. Therefore, t≧(2fff1.xtII,)D(4). fm
cx and t. Although it depends on the value of , generally t>D. That is, a vertically elongated elliptical beam is used for erasing.

Furthermore, in order to record information immediately after erasing information, the erasing beam, recording beam, and reproduction beam are irradiated close to each other on the same track of the disk.
9-7114 [As shown in Publication No. 1, for erasing beam and recording.

Separate semiconductor lasers were provided for reproduction, and these beams were combined. However, the semiconductor lasers used for recording and erasing are both high-output and expensive types.1 This requires the use of two such expensive semiconductor lasers, which leads to the problem that the equipment becomes expensive. there were.

[Purpose of the invention]

An object of the present invention is to provide a device suitable for recording three times immediately after erasing information using one semiconductor laser.

[Summary of the invention]

In order to achieve the above object, the present invention uses a polarizing beam splitter to separate a beam from a single semiconductor laser light source into two beams whose polarization directions are perpendicular to each other, and each is used as an erasing beam for recording and reproducing. Used as a beam for
The erasing beam and the recording and reproducing beams are arranged to irradiate the same track of the information recording medium in close proximity to each other. This will be explained with reference to FIG.

1 is a semiconductor laser light source, 2 is a collimator lens, 3 is 1
/4 wavelength plate, 4 is a polarizing beam splitter, 5 is a concave cylindrical lens, 6 is a convex cylindrical lens, 7 is a half mirror (non-polarizing beam splitter), 8 is a polarizing beam splitter, 9 is an objective lens, 10 is a disk, 11 is a track, 12 is a recording spot, 13 is a recording pit, 14 is a WhoU prism, 15 is a convex lens, 16 is a photodetector, 17 is a mirror,
18 is a convex cylindrical lens, 19 is a concave cylindrical lens, 20 is a mirror, 21 is an erase spot, and 22 is a marked edge pit.

The divergence angle of the diverging beam emitted from the semiconductor laser light source 1 is different in a direction parallel to the laser active layer and in a direction perpendicular to the laser active layer. In the drawings, parallel beams are shown by solid lines, and perpendicular beams are shown by broken lines. Also, the laser active layer is perpendicular to the plane of the paper. This diverging light becomes a parallel beam by the collimator lens 2 and enters the 1/4 wavelength plate 3 ◇1/4
The beam incident on the wavelength plate 3 is linearly polarized light (P polarization) with a polarization direction parallel to the plane of the paper, but the beam exiting the quarter wavelength plate 3 is circularly polarized light. This beam enters the polarizing beam splitter 4, where the P-polarized light is transmitted and the S-polarized light is reflected.

The beam transmitted through the polarizing beam splitter 4 is passed through a concave cylindrical lens 5. The convex cylindrical lens 6 expands the beam diameter in the direction parallel to the plane of the paper and shapes the beam into a nearly circular beam. This beam is incident on the half mirror 7, and approximately 50X is transmitted therethrough. The beam transmitted through the half mirror 7 enters the polarizing beam splitter 8, but since it is P-polarized, the beam is 100N
To Penetrate. This beam is focused by an objective lens 9,
Circular recording spot 1 on track 11 of disk 10
2 is irradiated to form recording pits 13.

On the other hand, the beam reflected by the first disk 10 passes through the objective lens 9 and then enters the polarizing beam splitter 8, but P
Since it is polarized light, it transmits 100X.

The transmitted beam enters the ＼-7 mirror 7, and is approximately 50X
It reflects. The beam reflected by the half mirror 7 passes through the Foucault prism 14. Photodetector 16 via convex lens 15
1 reproduction signal, focus error signal, and tracking error signal are detected. On the other hand, the beam reflected by the polarizing beam splitter 4 is reflected by the mirror 17. Convex cylindrical lens 18. Concave cylindrical lens 19. The beam diameter in the direction parallel to the plane of the paper is reduced by the mirror 20,
The beam is shaped into an oval beam. This beam enters the polarization beam splitter 8, but since it is S-polarized, it is 10
0X reflection. This beam is focused by an objective lens 9 and irradiates an oval erase spot 21 onto the track 11 of the disk 10, erasing the recorded pit 22.

The set angle of the mirror 20 is adjusted so that the erase spot 21 and the recording spot 12 are placed close to each other on the same track 11.

On the other hand, the beam reflected by the disk 10 is transmitted through the objective lens 9
'f: After passing, it enters the polarizing beam splitter 8, but 1
Since it is S-polarized light, it is reflected by 100X and does not enter the photodetector 16.

As shown in FIG. 3, the light intensity of the recording spot 12 and the erasing spot 21 is appropriately set based on the relationship between the irradiation light power density, irradiation time, and reflectance ratio of the recording material constituting the disk 1o.

Further, since the polarization directions of the recording spot 12 and the erasing spot 21 are perpendicular to each other and do not interfere with each other, there is no fear that they will interfere with each other even if they are quite close to each other.

Incidentally, since the recording spot 12 and the erasing spot 21 are formed by the same semiconductor laser light source 1, the erasing spot 21 is modulated by the same signal as the recording signal. Therefore, compared to the case where the erasing beam is continuously irradiated as in the conventional apparatus, it is necessary to set the actual irradiation time t to t=2 to (5). Therefore, the length t of the erasing spot 21 is tx2Vt, (6
).

Next, since the erasing beam 21 is intermittently irradiated, it is necessary to determine the lowest frequency of the recording signal so that no recorded pits 22 remain unerased.

That is, f,,lliyu=1/1=17C2tF,) (7). If you rewrite it, 'min = ”'If/L
(8) becomes.

According to the present invention, one semiconductor laser 1 can immediately record information after erasing it.

Note that the present invention is not limited to this example.

The present invention may apply to any configuration as long as the erasing beam and the recording/reproducing beam are two beams whose polarization directions are orthogonal to each other, obtained by separating the beam from one semiconductor laser light source using at least one polarizing beam splitter. Needless to say, it is included in

For example, 'M4 diagram is the cylindrical lens 5°6.1B in Figure 1.
, 19 is replaced by prisms 30, 31, 32, 33.

Further, instead of using the 11/4 wavelength plate 3, it is possible to use a 1/2 wavelength plate, or to tilt the direction parallel to the laser active layer of the semiconductor laser 1 by 45 degrees with respect to the plane of the paper.

Further, in this embodiment, an elliptical beam was created by beam shaping, but multiple beams using astigmatism or a diffraction grating may be used.

〔Effect of the invention〕

As described above, according to the present invention, since information can be recorded immediately after erasing using one semiconductor laser, the cost of the apparatus can be reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention, and FIG.
FIG. 3 is a graph showing the light intensity of the recording spot 12 and the erasing spot 21 in FIG. 2. FIG. It is a diagram. 1... Semiconductor laser light source 4... Polarizing beam splitter 8... Polarizing beam splitter 10... Disk 11... Track 12... Recording spot 21... Erasing spot

Claims (1)

[Claims] 1. In an optical information recording and reproducing apparatus that irradiates an erasing beam and a recording/reproducing beam closely onto the same track of an information recording medium and immediately records information after erasing the information, the erasing beam and the recording/reproducing beam are An optical information recording/reproducing device characterized in that a beam from one semiconductor laser light source is separated using at least one polarizing beam splitter to produce two beams whose polarization directions are orthogonal to each other.