JPS6310338A - Optical pickup device - Google Patents

Abstract

PURPOSE:To easily form an elliptic light spot on a recording medium by not using a cylindrical lens and using a semiconductor laser of multimode oscillation as a light source. CONSTITUTION:The beam emitted from a semiconductor laser 1 of multimode oscillation is collimated by a collimator lens 2 and has the optical path bent by a grating element 3 and is led to a beam splitter 4. This beam passes the beam splitter 4 and a condenser lens 5 and is converged on a recording medium 6 as an elliptic spot. The reflected light from the recording medium 6 is separated by the beam splitter 4 and is led to a beam splitter 8 through a converging lens 7 and is separated by the beam splitter 8, and a part of this light is made incident on a track error detector 9, and another part is made incident on a focus error detector 11 through a knife edge 10. Spot position error is detected by this reflected light.

Description

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

[Conventional technology]

Conventionally, in this type of optical pickup device, as a recording medium for recording information by light irradiation, there is one that utilizes a phase change between polycrystalline and amorphous, and the medium material is as follows. A Te-0-Ge-Sn alloy system or a Te-Se-Sn alloy system is used. A characteristic of these materials is that when a temperature change is applied to the material, they become amorphous when heated or cooled rapidly, and crystallized when heated or cooled relatively slowly. This phase change also changes the reflectance of the surface of the material, so the phase state can be determined by irradiating it with weak light. By using this phase change, it is possible to record, reproduce, and erase information.

In the optical disk shape, as a means to realize both phase changes from crystal to amorphous and from amorphous to crystal within one track width, as shown in the plan view of FIG. Some form circular spots 102 and oval spots 103 on top.

In FIG. 3, assuming that the recording medium 6 is moving at a constant speed in the direction of the arrow 101, the recording medium 6 is rapidly heated and cooled by the high power circular spot 102, and the relatively low power The oval spot 103 removes heat from the storage medium 6 and gradually cools it, thereby realizing the above means. Information bits are formed by this circular spot 102,
By erasing multiple information bits using the oval spot 103, recording and erasing can be realized every l track width.

FIG. 4 is a configuration diagram showing an example of a conventional optical pickup device, in which light emitted from a semiconductor laser 12 is directed onto a recording medium 6 via a collimating lens 13, a beam splitter 15, and a condensing lens 16. Converged. The reflected light from the recording medium 6 is separated in a beam splitter 15 and forms an oblong spot on the recording medium 6 in the case of a signal.

[Problem that the invention seeks to solve]

In the conventional optical pickup device described above, the cylindrical lens 14 is inserted into the collimated light in order to form an oval spot on the recording medium 6. However, in order for the long sleeve to form an oval spot of several μm (microns) to several tens of μm (microns), a lens with a long focal length is required as the cylinder 1 lens 14, which is difficult to manufacture. There are drawbacks.

[Means for solving problems]

The optical pickup device of the present invention is an optical pickup device including an optical system that irradiates a recording medium with light emitted from a semiconductor laser into a minute spot and guides the light from the recording medium to a photodetector, in which the semiconductor laser oscillates. It is configured to include a semiconductor laser whose axial mode is multi-mode, and an optical path conversion element that utilizes diffracted light from a transmission type or reflection type grating element between the semiconductor laser and the recording medium.

[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 light θ, the following equation holds true.

dsinθ=λ When the wavelength of the incident light changes by Δλ, the beam angle of the emitted light changes by Δθ given by the following equation.

Δθ=sin θ, (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), Δλ=Q,
3 nm and f = 4 mm (millimeter),
Then, f·(Δθ) to 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 becomes zero in response to a wavelength change of Δλ.
．． This results in a deviation of 7 μm. Since the diameter of the circular spot due to one axial mode is about 1 μmψ, when the semiconductor laser is in multi-mode oscillation,
An oblong spot with a length corresponding to the number of modes can be formed on the recording medium. 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 or the like.

A diffraction efficiency of 70 or more can be achieved by blazing the grating or the like.

〔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 a semiconductor laser 1, a collimating lens 2, a grating element 3, a beam splitter 4, a condensing lens 5, and a converging lens, corresponding to a recording medium 6. 7, a beam splitter 8, a track error detector 9, a knife 10, and a focus error detector 11. Note that the oscillation axis mode of the semiconductor laser 1 is formed by multiple modes.

In FIG. 1, an emitted beam from a semiconductor laser 1 that emits multi-mode oscillation is collimated by a collimating lens 2, has an optical path bent by a grating element 3, and is guided to a beam splitter 4. Further, the light is focused onto the recording medium 6 via the beam splitter 4 and the condensing lens 5 as an elliptical spot. The reason why the oval spot is formed on the recording medium 6 is that the light emitting point of the semiconductor laser 1 is multi-mode. The reflected light from the recording medium 6 is separated at the beam splitter 4,
The beam is guided to a beam splitter 8 through a converging lens 7, separated at the beam splitter 8, and a part of it is sent to a track error detector 9, and a part of it is sent to a knife lens 10, where a spot position error is detected from the focus error emitted light. . In this embodiment, the grating element 3 also has a beam shaping function of circularizing an elliptical beam.

Note that the grating element 3 may be placed between the beam splitter 4 and the condenser lens 5.

As described above, the optical pickup device of this embodiment is applied as an erasing head that forms an oblong spot on the recording medium 6, but a separate light source that forms a circular spot using a predetermined wavelength filter or the like is used. It is also possible to configure a multi-beam type optical pickup device capable of recording and erasing by combining the beams emitted by the .

〔Effect of the invention〕

As explained above, the present invention can extremely easily form an elliptical spot on a recording medium by using a multi-mode oscillation semiconductor laser as a light source without using a cylindrical lens, which is problematic in manufacturing. This has the advantage that it is possible to provide an optical pickup device that can perform

-82・,

[Brief explanation of the drawing]

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 invention in detail, and Fig. 3 is a diagram showing a beam spot on a recording medium. , FIG. 4 is a diagram showing the 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% 5116...Condensing lens, 6
...Storage medium, 7...Convergent lens, 9
...Track error detector, 10...
knife, 11... focus error detector, 12... semiconductor laser, 14...
Cylindrical lens, 17...detection optical system. □Sr $ / Sen $ 2 Figure

Claims (1)

[Claims] In an optical pickup device comprising an optical system that irradiates a recording medium with light emitted from a semiconductor laser into a minute spot and guides the light from the recording medium to a photodetector, the semiconductor laser is a semiconductor whose oscillation axis mode is multimode. An optical pickup device comprising: a laser; and an optical path changing element that utilizes diffracted light from a transmission or reflection grating element between the semiconductor laser and the recording medium.