JPH0610883B2 - 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.

[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 15 is the collimating lens 17
Is collimated by the laser beam, is reflected by the polarization beam splitter 21, and is condensed as a circular spot on the recording medium 6 via the quarter-wave plate 20 and the condenser lens 19. The reflected light from the recording medium 6 is collected by the condenser lenses 19 and 1.
It is guided to the detection optical system 25 via the / 4 wavelength plate 20, the polarization beam splitter 21, the ¼ wavelength plate 22 and the wavelength filter 23. On the other hand, the emitted light from the semiconductor laser 16 forming the elliptical spot passes through the collimator lens 18 and the cylindrical lens 24, is reflected by the polarization beam splitter 21, and is passed through the quarter wavelength plate 22 to the wavelength filter 23. To reach. 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: A 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 among the light emitting points can be switched between a single mode and a multi mode depending on a driving state; A laser drive circuit that switches the oscillation axis mode of the semiconductor laser, and an optical path conversion element that uses the diffracted light of a transmissive or reflective grating element between the semiconductor laser and the recording medium. It

[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. As for the diffraction efficiency of light, sufficient diffraction efficiency is realized by blazing the grating.

As the laser light source, an array type semiconductor laser capable of independently driving a plurality of light emitting points is used, and the oscillation axis mode of at least one light emitting point is switched between multimode and single mode. To be set. As a method of switching the oscillation axis mode of the array-type semiconductor laser, a method of superposing a high-frequency current on the array-type semiconductor laser that oscillates a single mode by direct current driving to make it into a multimode, and an electrode of the array-type semiconductor laser There is a method of switching between the single mode and the multi mode by dividing the element in the resonator length direction and changing the value of the drive current flowing through each electrode.

In the array type semiconductor laser, assuming that all light emitting points oscillate in a single mode by direct current drive and are made into a multimode by superposition of high frequency currents, the arrangement of circular spots and elliptical spots on the recording medium is arbitrary. In addition, when there are three or more light emitting points, it is possible to realize complicated functions including checking the state of a recording medium such as a disc before and after recording or before and after 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. A track error detector 9, a knife edge 10, a focus error detector 11, a direct current circuit 12, a high frequency circuit 13, and a switching circuit 14, and are configured corresponding to the recording medium 6. . The DC circuit 12, the high frequency circuit 13 and the switching circuit 14 form a laser drive circuit for switching the oscillation axis mode of the array type semiconductor laser 1.

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. To the focus error detector 11 via 10,
Each is incident. 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 grating element 3
The arrangement position of may be set between the beam splitter 4 and the condenser lens 5.

When recording and reproducing operations are performed, a light emitting point of the array-type semiconductor laser 1 that performs recording and reproducing operations is driven through direct current or low frequency by the direct current circuit 12 to form a predetermined circular spot on the recording medium. 6 is formed. In the case of performing the erasing operation, a light emitting point to be erased in the array type semiconductor laser is driven by superimposing the high frequency current by the high frequency circuit 13 on the direct current or the low frequency to record a predetermined elliptical spot. It is formed on the medium 6. Note that switching control is performed via the switching circuit 14 to separate the high frequency current superposition.

〔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, 17,
18 ... Collimating lens, 3 ... Grating element, 4, 8 ... 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, 15,16 ...... Semiconductor laser, 20,22 ...... 1/4 wavelength plate, 21 ... Polarizing beam splitter, 23 ... Wavelength filter, 24 ... Cylindrical lens, 25 ... 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. A semiconductor laser having a plurality of drivable light emitting points, wherein an oscillation axis mode of at least one of the light emitting points is switched between a single mode and a multi mode depending on a driving state; A laser drive circuit that switches the oscillation axis mode of a laser, and an optical path conversion element that uses the diffracted light of a transmissive or reflective grating element between the semiconductor laser and the recording medium. Pickup device.