JPH0766559B2 - Optical pickup device - Google Patents

Description

The present invention relates to an optical pickup device, and more particularly to an optical pickup device applied to an optical information recording device that records, reproduces, and erases information by light irradiation.

[Conventional technology]

Conventionally, in this type of optical pickup device, as a recording medium for recording information by light irradiation, there is a recording medium that utilizes a phase change between polycrystalline and amorphous. -Ge-Sn alloy system or Te-Se
-Sn alloy system is used. A characteristic of these materials is that when a temperature change is applied to the materials, they are made amorphous by rapid heating and rapid cooling, and crystallized by relatively slow heating and cooling. This phase change also changes the reflectance of the surface of the material, so the phase state can be known by irradiating weak light.
By using this phase change, it is possible to record, reproduce and erase information.

As shown in the plan view of FIG. 3, on the recording medium 6, as shown in the plan view of FIG. 3, in order to realize both the phase change from the crystal to the amorphous and the phase change from the amorphous to the crystal within the optical disc shape. To form a circular spot 102 and an oval spot 103 relative to. In FIG. 3, assuming that the recording medium 6 is moving in the direction of arrow 101 at a constant speed, the circular spot 102 having a high power causes the recording medium 6 to be rapidly heated and cooled, so that the ellipse has a relatively low power. The spot 103 gradually heats and cools the recording medium 6 to realize the above means. When the information bit is formed by the circular spot 102 and the information bit is erased by the oval spot 103, 1
Recording and erasing can be realized for each track width.

FIG. 4 is a block diagram showing an example of a conventional optical pickup device. The emitted light of the semiconductor laser 12 is a collimator lens 13, a bead splitter 15, and a condenser lens 16.
It is converged on the recording medium 6 via. The reflected light from the recording medium 6 is separated by the beam splitter 15 and guided to a detection optical system 17 for detecting a signal and an error. In this case, in order to form an oval spot on the recording medium 4, the cylindrical lens 14 shown by the broken line in FIG. 4 is inserted into the collimated light.

[Problems to be solved by the invention]

In the conventional optical pickup device described above, the cylindrical lens 14 is inserted into the collimated light in order to form the elliptical spot on the recording medium 6. However, in order to form an elliptical spot having a long axis of several μm (microns) to several tens of μm (microns), a lens having a long focal length is required as the cylindrical lens 14, which is difficult to manufacture. There are drawbacks.

[Means for solving problems]

An optical pickup device of the present invention is an optical pickup device including an optical system that irradiates a recording medium with emitted light of a semiconductor laser as a minute spot and guides the light from the recording medium to a photodetector. A semiconductor laser having an axial mode of multi-mode, and an optical path conversion element that uses the diffracted light of a transmission type or reflection type grating element having different diffraction angles depending on the wavelength between the semiconductor laser and the recording medium. To be done.

[Action]

In FIG. 2, considering the case where light of wavelength λ is incident as incident light θ on the transmission type grating element 3 having a pitch of d, the following formula is established.

dsin θ = λ When the wavelength of the incident light changes by Δλ, the beam angle of the outgoing light changes by Δθ in the following equation.

Δθ = sin θ · (Δλ / λ) When the focal length of the condenser lens is f, the spot center shifts by f · (Δθ) on the recording medium. θ = 3
0, λ = 800 nm (nanometer), Δλ = 0.3 nm and f
= 4 mm (millimeter meter), then f · (Δθ)
It becomes 0.7 μm (micron). On the other hand, the axial mode interval of a semiconductor laser with a cavity length of 300 μm is about 0.3 nm, so Δ
The spot position shifts by 0.7 μm between the adjacent axis modes according to the change in the wavelength of λ. Since the size of the circular spot diameter due to one axis mode is about 1 μmφ, an elliptical spot having a length corresponding to the number of modes is formed on the recording medium when the semiconductor laser is oscillating in multimode. be able to. This also applies to the case where a reflective grating element is used instead of the grating element. The grating element is not limited to a simple grating, and may be an off-axis type zone plate lens used in place of a condenser lens or the like. As for the diffraction efficiency, it is possible to achieve an efficiency of 70% or more by blazing the grating.

〔Example〕

 Hereinafter, the present invention will be described 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, in this embodiment, the semiconductor laser 1, the collimator lens 2, the grating element 3, the beam splitter 4, the condenser lens 5, and the converging lens are provided corresponding to the recording medium 6. 7, a beam splitter 8, a track error detector 9, a knife edge 10, and a focus error detector 11. The oscillation axis mode of the semiconductor laser 1 is formed by a multi mode.

In FIG. 1, a beam emitted from a semiconductor laser 1 that oscillates in multimode is collimated by a collimator lens 2, an optical path is bent by a grating element 3, and is guided to a beam splitter 4. Further, it is converged as an oval spot on the recording medium 6 via the beak splitter 4 and the condenser lens 5. The reason why the elliptical spot is formed on the recording medium 6 is that the light emitting point of the semiconductor laser 1 is in the multimode. The reflected light from the recording medium 6 is separated by the beam splitter 4,
The light is guided to the beam splitter 8 via the converging lens 7, separated by the beam splitter 8, and a part thereof is incident on the track error detector 9 and a part is incident on the focus error detector 11 via the knife edge 10 respectively. It A spot position error is detected by these reflected lights. In this embodiment, the grating element 3 also has a beam shaping function for circularizing the elliptical beam. The grating element 3 may be arranged between the beam splitter 4 and the condenser lens 5.

The optical pickup device of this embodiment is applied as an erasing head for forming an elliptical spot on the recording medium 6 as described above, but another light source for forming a circular spot using a predetermined wavelength filter or the like. It is also possible to configure a multi-beam type optical pickup device capable of recording and erasing by combining with the emitted beam by the.

[Effects of the Invention] As described above, according to the present invention, a semiconductor laser of multi-mode oscillation is used as a light source without using a cylindrical lens, which is problematic in manufacturing. There is an effect that an optical pickup device capable of forming a circular spot can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention, FIG. 2 is a conceptual diagram of a transmission type grating element for explaining the operation of the present invention, and FIG. 3 is a diagram showing a beam spot on a recording medium. , FIG. 4 is a diagram showing a configuration of a conventional optical pickup device. In the figure, 1 ... Array type semiconductor laser, 2, 13 ... Collimating lens, 3 ... Grating element, 4, 8, 15 ...
… Beam splitter, 5,16 …… Condenser lens, 6 …… Recording medium, 7 …… Convergent lens, 9 …… Track error detector, 10 …… Knife edge, 11 …… Focus error detector, 12 …… Semiconductor laser, 14 ... Cylindrical lens, 17 ... Detection optical system.

Claims (1)

[Claims] 1. An optical pickup device comprising an optical system for irradiating a recording medium with emitted light of a semiconductor laser as a minute spot and guiding the light from the recording medium to a photodetector, wherein the semiconductor laser has an oscillation axis mode. On the recording medium, a multimode semiconductor laser and an optical path conversion element that uses diffracted light of a transmission type or reflection type grating element having different diffraction angles depending on wavelengths are provided between the semiconductor laser and the recording medium. An optical pickup device, characterized in that an elliptical spot is formed on the surface.