JPH0610884B2 - 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 which utilizes a phase change between polycrystalline and amorphous. As the medium material, Te-O is used. -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, from an optical pickup device to a storage medium, a means for realizing both phase changes from crystal to amorphous and amorphous color crystal within one track width in the shape of an optical disc is shown. 6 to form a circular spot 102 and an oval spot 103 on the upper surface. In FIG. 3, the recording medium 6 is indicated by an arrow 1.
Assuming that the storage medium 6 is moving at a constant speed in the direction 01, the storage medium 6 is rapidly heated and cooled by the high power circular spot 102, and the storage medium 6 is gradually heated by the relatively low power oval spot 103. The slow cooling is performed to realize the above means. If the information bit is formed by the circular spot 102 and the information bit is erased by the oval spot 103, 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, in which the emitted light of the semiconductor laser 15 passes through the collimator lens 16, the beam splitter 18 and the condenser lens 19 and is recorded on the recording medium 6. Converged. The reflected light from the recording medium 6 is separated by the beam splitter 18 and guided to a detection optical system 20 for detecting a signal and an error. In this case, in order to form an oval spot on the recording medium 6, the cylindrical lens 17 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 17 is inserted in the collimated light in order to form the elliptical spot 102 on the recording medium 6. Therefore, the spot formed on the recording medium 6 by the optical pickup device is limited to the elliptical spot, and the circular spot cannot be formed. Therefore, it is used in combination with an optical pickup device that forms another circular spot, or is a multi-beam type that forms two spots of a circular shape and an oval shape by combining lights of different wavelengths with a wavelength filter. It is necessary to consider making the optical pickup device, and there is a drawback that the configuration of the optical pickup device becomes complicated.

[Means for solving problems]

The optical pickup device of the present invention is an optical pickup device provided with 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, which is driven as the semiconductor laser. A semiconductor laser whose oscillation axis mode is switched between a single mode and a multimode depending on a state, a laser drive circuit which switches the oscillation axis mode of the semiconductor laser, and between the semiconductor laser and the recording medium, And an optical path conversion element that uses the diffracted light of a transmission type or reflection type grating element.

[Action]

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 angle changes by Δλ, the beam angle of the emitted 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 (nanometers), Δλ = 0.
If 3 nm and f = 4 mm (millimeters), then f
・ (Δθ) becomes 0.7 μm (micron). On the other hand, since the axial mode interval of a semiconductor laser having a cavity length of 300 μm is about 0.3 nm, the spot position is deviated by 0.7 μm between the adjacent axial modes according to the wavelength change of Δλ. Since the size of the circular spot diameter due to one axis mode is about 1 μmφ, when the semiconductor laser is oscillating in multimode, an elliptical spot having a length corresponding to the number of modes is formed on the recording medium. can do. That is, when a transmission type grating element is used in the optical system of the optical pickup device, the elliptical spot is easily formed on the recording medium by making the oscillation axis modes of the semiconductor laser multi. The same effect can be obtained by using diffracted light from a reflective grating element instead of a transmissive grating element. Further, the grating element is not limited to a simple grating, but may be an off-axis type zone plate lens used in place of a condenser lens or the like. The light diffraction efficiency can be 70% or more by blazing the grating.

When the grating element is provided in the optical path, the oscillation axis mode of the semiconductor laser is switched between the single mode and the multimode, so that two kinds of spots, a circular shape and an oval shape, are easily formed on the recording medium. To be done. As a method of switching the oscillation axis mode of the semiconductor laser, a method of superposing a high-frequency current on a laser that oscillates a single mode by direct current drive to make it a multimode, and dividing the electrodes of the semiconductor laser in the cavity length direction However, there is a method of controlling the number of oscillation modes by changing the ratio of the currents applied to the respective electrodes.

〔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, this embodiment is based on the semiconductor laser 1
, Collimating lens 2, grating element 3,
Beam splitter 4, condenser lens 5, and condenser lens 7
, Beam splitter 8 and track error detector 9
, Knife edge 10 and focus error detector 11
, DC circuit 12, high frequency circuit 13, and switching circuit 14
And are provided corresponding to the recording medium 6.
The DC circuit 12, the high frequency circuit 13, and the switching circuit 1
Reference numeral 4 forms a laser drive circuit for switching the oscillation axis mode of the semiconductor laser 1.

In FIG. 1, the emitted beam from the semiconductor laser 1 is
The beam splitter 4 is collimated by the collimator lens 2 and the optical path is bent by the grating element 3.
Sent to. 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. When performing recording and reproducing operations, the semiconductor laser 1 is driven by the direct current circuit 12 through direct current or low frequency to form a predetermined circular spot on the recording medium 6, and when performing erasing operation. Through the connection control operation by the switching circuit 14,
By driving the semiconductor laser 1 by superimposing the high-frequency current by the DC or low frequency, a predetermined elliptical spot is formed on the recording medium 6.

〔The invention's effect〕

As described above, according to the present invention, it is possible to form not only an elliptical spot necessary for erasing but also a circular spot necessary for recording and reproduction on a recording medium with a relatively simple structure. There is an effect that an optical pickup device 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 shows a beam spot on a recording medium. FIG. 4 and FIG. 4 are diagrams showing a configuration of a conventional optical pickup device. In the figure, 1,15 ... Semiconductor laser, 2,16 ...
Collimating lens, 3 ... Grating element, 4,
8, 18 ... Beam splitter, 5, 19 ... Condensing lens, 6 ... Recording medium, 7 ... Converging lens, 9 ... Track error detector, 10 ... Knife edge, 11 ... Focus error detector , 12 ... DC circuit, 13 ... high frequency circuit, 14 ... switching circuit, 17 ... cylindrical lens, 20 ... detection optical system.

Claims (1)

[Claims] 1. An optical pickup device including 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. A semiconductor laser whose axis mode is switched between a single mode and a multimode, a laser drive circuit which switches the oscillation axis mode of the semiconductor laser, and a transmission type or a laser diode between the semiconductor laser and the recording medium. An optical pickup device comprising: an optical path conversion element that uses diffracted light from a reflective grating element.