JPS637528A - Optical pickup device - Google Patents

Abstract

PURPOSE:To attain the formation of a circular spot, and an elliptic spot, by providing a semiconductor laser in which the oscillation axis mode of one luminous point out of plural luminous points capable of being driven independently, is a multi-mode, and an optical path conversion element in which use is made of the diffracted light of a transmission or reflection type grating element. CONSTITUTION:A beam emitted from an array type semiconductor laser 1 is collimated by a collimator lens 2, and its optical path is bent by a grating element 3, and it is sent to a beam splitter 4, and is converged on a recording medium 6 as a spot through the beam splitter 4, and a condenser lens 5. In this case, the circular spot is formed if the luminous point is a single mode, and the elliptic spot is formed if it is the multi-mode. The reflected light from the recording medium 6 is made incident on a beam splitter 8 through the beam splitter 4, and a convergent lens 7, and it is separated at the beam splitter 8, and a part of it is made incident on a track detector 9, and the other part of it is made incident on a focus error detector 11 through a knife edge 10, respectively, and a spot position error can be detected by those reflected light. In this way, the formation of the circular, and the elliptic spots can be easily performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device, and particularly to an optical pickup device suitable for an optical information recording device that records, reproduces, and erases information by irradiating light.

[Conventional technology]

Conventionally, in this type of optical pickup device, the recording medium for recording information by light irradiation has been one that utilizes a phase change between polycrystalline and amorphous, and the material for this medium is Te- A 0-G e -S n alloy system or a Te-8e-8n alloy system is used. A characteristic of these materials is that when a temperature change is applied to the material, they become amorphous when rapidly heated or rapidly cooled, and crystallized when heated or cooled relatively slowly.

Due to this phase change, the reflectance of the surface of the material also changes, so the phase state can be determined by weak +1 irradiation. By using this phase change, information recording,
It is possible to play and erase.

In the optical disk shape, as a means to realize phase change from crystal to amorphous and from amorphous to crystal within the EL track width, as shown in the plan view of FIG. There is a circular spot 102 and an oblong spot 103' formed on the top. In FIG. 3, the recording medium 6 is indicated by the arrow 1
Assuming that the medium 6 is moving at a constant speed in the direction 01, the medium 6 is rapidly heated and cooled by the circular spot 102 with high power, and the oval spot 1 with relatively low power
03, the recording medium 6 is kept warm and slowly cooled, thereby realizing the above-mentioned means. By forming information bits using the circular spot 102 and erasing the information bits using the oval spot 103, recording and erasing can be realized for each track width.

[Problem that the invention seeks to solve]

As shown in FIG. 4, the conventional optical pickup device described above uses a method of combining the light emitted from two semiconductor lasers with different wavelengths in order to form a circular spot and an oval spot. ing. In FIG. 4, the emitted light from the semiconductor laser 12 is transmitted through the collimating lens 14.
is di-collimated, reflected by the polarizing beam splitter 18, and transmitted to the % wave plate 17 and the condenser lens 16.
The light is focused as a circular spot on the recording medium 6 through the . The reflected light from the recording medium 6 is guided to a detection optical system 22 via a condenser lens 16, a wavelength plate 17, a polarization beam splitter 18, a wavelength plate 19, and a wavelength filter 20. - On the other hand, a semiconductor laser 13 forming an oval spot
The emitted light from the duck passes through the collimating lens 15 and the cylindrical lens 21, and is polarized by the polarized beam splitter 18.
, and reaches the wavelength filter 20 via the wavelength plate 19 . Light of this wavelength is reflected and focused onto the recording medium 6. However, this conventional optical start-up device has disadvantages in that its configuration is complicated, its shape is large, and it is difficult to align the focus of the circular spot and the oval spot.

[Means for solving problems]

The original pickup device of the present invention is the emitted light of a semiconductor laser? An optical pickup device comprising an optical system that irradiates a recording medium in the form of a minute spot and guides light from the recording medium to a photodetector, the semiconductor laser having a plurality of light emitting points each of which can be driven independently; and a semiconductor laser in which at least one of the light emitting points has a multi-mode oscillation axis mode, and a diffracted light from a transmission type or reflection type grating element is provided between the semiconductor laser and the recording medium. and an optical path conversion element to be used.

[Effect]

In FIG. 2, if we consider the case where light with a wavelength λ is incident on the transmission grating element 3 with a pitch of d at an incident angle θ, the following equation holds true.

d sin θ=λ When the wavelength of the incident light changes by Δλ, the beam angle of the output light changes by Δθ given by the following equation.

Δθ=sinθ·(Δλ/λ) If the focal length of the condenser lens is f, then the spot center will be shifted by f·(Δθ) on the recording medium. θ=3
0°, λ=800nm (nanometer), △λ”0.
3 nm and f = 4 mm (millimeter), then f·(Δθ) ~ 0.7 μm (micron).

- On the other hand, since the axial mode spacing of a semiconductor laser with a cavity length of 300 μm is approximately Q, 3 nm, the spot position between adjacent axial modes is 0.7 μm in response to the wavelength change of Δλ.
It will shift. Since the diameter of a circular spot due to one axial mode is approximately 1 μmφ, when the semiconductor laser is in multi-mode oscillation, an elliptical spot with a length corresponding to the number of modes is formed on the recording medium. be able to. This effect is the same when a reflective grating element is used instead of the grating element. The grating element may be not only a simple grating but also an off-axis zone plate lens used in place of a condenser lens, and a blazed grating can also provide sufficient diffraction efficiency.

As a light source, use an array-type semiconductor laser that can drive multiple light-emitting points independently, and if the axial mode of at least one light-emitting point is multimode and the other light-emitting points are single mode. Both a circular spot and an oval spot can be easily formed using the grating element.

When there are three or more light emitting points of the light source, it becomes possible not only to record and erase, but also to check, review, etc. the state of the disc before and after recording or before and after erasing.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. As shown in FIG. 1, this embodiment includes an array type semiconductor laser 1, a collimating lens 2, a grating element 3, a beam splitter 4, a condensing lens 5, a converging lens 7, a beam splitter, The camera is configured to correspond to the recording medium 6.

In FIG. 1, an emitted beam from an array type semiconductor laser 1 is collimated by a collimating lens 2, has an optical path bent by a grating element 3, and is sent to a beam splitter 4. Furthermore.

The light is focused as a spot on the recording medium 6 via the beam splitter 4 and the condensing lens 5. In this case, if the light emitting point is in a single mode, a circular spot is formed, and if the light emitting point is in a multimode, an elliptical spot is formed. The reflected light from the recording medium 6 is incident on the beam splitter 8 via the beam splitter 4 and the converging lens 7, and is separated at the beam splitter 8. The light beams are respectively incident on the focus error detector 11 via the respective focus error detectors 11. A spot position error is detected from these reflected lights. In the configuration of this embodiment, the grating element 3 also has a beam shaping function for making a circular beam circular. Note that the grating element 3 may be arranged between the beam splitter 4 and the condenser lens 5.

Note that when multiple light-emitting points of an array-type semiconductor laser emit light simultaneously and the reflected light from each spot corresponding to each light-emitting point is received individually, the reflected beams are focused and separated, and the array-type semiconductor laser It is sufficient to receive light from each source using a detector or the like.

〔Effect of the invention〕

As described above, the present invention has the advantage of being able to provide a source pickup device that can easily form predetermined circular spots and oval spots with a relatively simple configuration.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a conceptual diagram of a transmission grating element for explaining the present invention in detail, and Fig. 3 is a recording medium. The diagram showing the upper beam spot, FIG. 4, is a diagram showing the configuration of a conventional optical pickup device. In the figure, 1...Array type semiconductor laser, 2
゜14.15...Collimating lens, 3...
...Grating element, 4,8...Beam splitter, 5゜16...Condensing lens, 6...
...Recording medium, 7...Focusing lens, 9...
....Track error detector, 10 ..... knife, 11 ..... focus error detector,
12.13... Semiconductor laser, 17.19...
..... Wave plate, 18 .... Polarizing beam splitter, 20 .... Wavelength filter, 21 ....
・Cylindrical lens, No. 2 / Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] In an optical pickup device comprising an optical system that irradiates a recording medium with emitted light from a semiconductor laser in the form of a minute spot and guides the light from the recording medium to a photodetector, the semiconductor lasers include a plurality of independently drivable lasers. a semiconductor laser having a light emitting point and in which the oscillation axis mode of at least one of the light emitting points is multimode, and a transmission type or reflection type grating between the semiconductor laser and the recording medium. An optical pickup device comprising: an optical path conversion element that utilizes diffracted light of the element.