JPH0792926B2 - Optical pickup device - Google Patents

Description

The present invention relates to an optical pickup device, and more particularly to an optical pickup device adapted to an optical information recording device for recording, reproducing and erasing 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 which 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. Due to this phase change, the reflectance of the surface of the material also changes,
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, as a means for realizing a phase change from crystal to amorphous and from amorphous to crystal within one track width in the shape of an optical disk, as shown in the plan view of FIG. Some form a circular spot 102 and an oblong spot 103 to the top. 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 of high power causes the recording medium 6 to be rapidly heated and rapidly cooled, resulting in a relatively low power. The circular spot 103 gradually heats and slowly cools the recording medium 6 to realize the above means. If information bits are formed by the circular spots 102 and information bits are erased by the oval spots 103, recording and erasing can be realized for each track width.

[Problems to be solved by the invention]

As shown in FIG. 4, the above-mentioned conventional optical pickup device uses a method of combining emitted lights from two semiconductor lasers having different wavelengths in order to form a circular spot and an oval spot. ing. In FIG. 4, the light emitted from the semiconductor laser 12 is collimated by the collimator lens 14, reflected by the polarization beam splitter 18, and passed through the quarter-wave plate 17 and the condenser lens 16 onto the recording medium 6. It is collected as a circular spot. The reflected light from the recording medium 6 is guided to the detection optical system 22 via the condenser lens 16, the 1/4 wavelength plate 17, the polarization beam splitter 18, the 1/4 wavelength plate 19 and the wavelength filter 20. On the other hand, the emitted light from the semiconductor laser 13 forming the elliptical spot passes through the collimating lens 15 and the cylindrical lens 21, is reflected by the polarization beam splitter 18, and
It reaches the wavelength filter 20 via the wave plate 19. Light of this wavelength is reflected and condensed on the recording medium 6. However, this conventional optical pickup device has the drawbacks that the configuration is complicated and the shape is large, and it is difficult to focus the circular spot and the elliptical spot.

[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 emitted light of a semiconductor laser as a minute spot and guides light from the recording medium to a photodetector, wherein the semiconductor laser is: An array type semiconductor laser having a plurality of light emitting points that can be independently driven, and an oscillation axis mode of at least one of the light emitting points is a multimode, the semiconductor laser, and the recording medium. And an optical path conversion element that utilizes the diffracted light of a transmissive or reflective grating element having a different diffraction angle depending on the wavelength.

[Work]

In FIG. 2, considering the case where light of wavelength λ is incident on the transmissive grating element 3 having a pitch of d at an incident angle θ, the following equation holds.

d sin 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 = 30
If ゜, λ = 800nm (nanometer), Δλ = 0.3nm and f = 4mm (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 may be not only a simple grating but also an off-axis type zone plate lens used in place of a condenser lens or the like, and a blazed type grating can sufficiently obtain diffraction efficiency.

As the light source, an array-type semiconductor laser capable of independently driving a plurality of light emitting points is used, and if at least one light emitting point has a multi-mode axial mode and the other light emitting points are a single mode. Both the circular spot and the oval spot can be easily formed by the grating element. If the light source has three or more emission points,
In addition to recording and erasing, it is possible to check the disc state before and after recording or erasing.

〔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, an array type semiconductor laser 1, a collimating lens 2, a grating element 3, a beam splitter 4, a condenser lens 5, a condenser lens 7, and a beam splitter 8 are used. , Track error detector 9, knife edge 10, focus error detector 11
And are provided corresponding to the recording medium 6.

In FIG. 1, the beam emitted from the array type semiconductor laser 1 is collimated by the collimator lens 2, the optical path is bent by the grating element 3, and is sent to the beam splitter 4. Further, it is converged as a spot on the recording medium 6 via the beam splitter 4 and the condenser lens 5. In this case, a circular spot is formed when the light emitting point is in the single mode, and an elliptical spot is formed when the light emitting point is in the multi mode. The reflected light from the recording medium 6 enters the beam splitter 8 via the beam splitter 4 and the converging lens 7 and is separated by the beam splitter 8, part of which is the track error detector 9 and part of which is the knife edge. The light is incident on the focus error detector 11 via 10. 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 circularizing the elliptical beam. The arrangement position of the grating element 3 may be set between the beam splitter 4 and the condenser lens 5.

In addition, when a plurality of light emitting points of the array type semiconductor laser are simultaneously emitted and the reflected light from each spot corresponding to each light emitting point is individually received, the reflected beam is focused and separated to obtain the array type light. Each light may be received by a detector or the like.

〔The invention's effect〕

As described above, the present invention has an effect that it is possible to provide an optical pickup device that can easily form a predetermined circular spot and elliptical spot with a relatively simple configuration.

[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, 14, 15 ...
… Collimating lens, 3 …… Grating element, 4,8
...... Beam splitter, 5,16 ...... Condenser lens, 6 …… Recording medium, 7 …… Focusing lens, 9 …… Track error detector, 10 …… Knife edge, 11 …… Focus error detector, 12, 13 …… Semiconductor laser, 17,19 …… 1/4 wave plate, 18
...... Polarizing beam splitter, 20 …… Wavelength filter, 21…
… Cylindrical lens, 22… 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 each of the semiconductor lasers is independently provided. An array type semiconductor laser having a plurality of drivable light emitting points, and the oscillation axis mode of at least one of the light emitting points being a multimode, and between the semiconductor laser and the recording medium. 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, and a circular spot and an oval spot are simultaneously formed on the recording medium. apparatus.