JPS6310339A - Optical pickup device - Google Patents

Abstract

PURPOSE:To easily form circular and elliptic light spots by providing a grating element in the optical path and switching the oscillation axis mode of a semiconductor laser to the single mode or the multimode. CONSTITUTION:The beam emitted from a semiconductor laser 1 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 and passes the beam splitter 4 and a condenser lens 5 and is converged on a recording medium 6 as a spot. In this case, the circular spot is formed if the light emission point is in the single mode, but the elliptic spot is formed if it is in the multimode. The reflected light from the recording medium 6 passes the beam splitter and a converging lens 7 and is made incident on a beam splitter 8 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 more particularly to an optical pickup device applied to an optical information recording device that records, reproduces, and erases information by irradiating light.

[Conventional technology]

Conventionally, in this glaze optical system, F'i.

A recording medium that records information by light irradiation is one that utilizes phase change between polycrystalline and amorphous. Materials for this medium include ri%Te-〇-Ge-8H alloy system or rjTe-8e. -8n alloy type etc. are used. What are the characteristics of these materials?

When subjecting a material to temperature changes, it becomes amorphous if it is rapidly heated or rapidly cooled, and crystallized if it is 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 a circular spot 102 and an oblong spora) 103 on the medium 6. In FIG. 3, assuming that the recording medium 6 is moving at a constant speed in the direction of the arrow 101,
The storage medium 6 is rapidly heated and cooled by the high power circular spora) 102, and the oval spora with relatively low power is generated.
103 performs heat removal and slow cooling of the storage medium 6, thereby realizing the above means. By forming information bits using the circular spot 102 and erasing the information bits using the oval spot 103, recording and erasing can be realized for each width.

FIG. 4 is a block diagram showing an example of a conventional optical pickup device, in which the emission +rt of the semiconductor laser 15,
Collimating lens 16. The light is focused onto the recording medium 6 via the beam splitter 18 and the condensing lens 19. The reflected light from the recording medium 6 is separated by a beam splitter 18 and sent to a detection optical system 20 for signal and error detection.
guided by.

In this case, a cylindrical lens 17 shown by a broken line in FIG. 4 is inserted into the collimated light to form an oval cedar 9 on the recording medium 6.

[Problem that the invention seeks to solve]

In the conventional optical start-up device described above, a cylindrical lens 17 is inserted into the collimated light in order to form an elliptical curve 102 on the 1-1° recording medium 6. Therefore, the spots formed on the recording medium 6 by this optical pickup device are limited to only oval spots, and it is impossible to form circular spots. For this reason, a multi-beam type optical pickup device that forms two circular and oval spots can be used in combination with another optical pickup device that forms a circular spot, or a multi-beam type that combines light of different wavelengths using a wavelength filter to form two circular and oval spots. It is necessary to consider the possibility of incorporating an optical pickup device, which has the disadvantage of complicating the configuration of the optical pickup device.

[Means for solving problems]

The optical pickup device of the present invention makes the emitted light of a semiconductor laser into a minute beam and irradiates it onto a recording medium.

An optical pickup device comprising an optical system that guides light from the recording medium to a photodetector, wherein the semiconductor laser is a semiconductor laser whose oscillation axis mode is switched between a single mode and a multimode depending on the driving state; A laser drive circuit that switches the oscillation axis mode of the laser, and an optical path conversion element that utilizes diffracted light from a transmissive or reflective grating element between the semiconductor laser and the recording medium. Ru.

[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 within the incident range 0, a linear equation holds true.

dsinθ=λ When the wavelength of the incident light changes by △λ, the beam angle of the output light 1
It changes by △θ of the following equation.

If the focal length of the condensing lens is f, then the spot center will be shifted by f·(Δθ) on the recording medium. θ=3
0°, λ=800nm (nanometer), △λ=Q,
Assuming 3nm and f=4wn (millimeter),
!・(Δθ) ~ 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 center is 0.7 μm between adjacent axial modes in response to the wavelength change of Δλ.
It will shift. Since the diameter of a circular spot due to one axial mode is approximately 1 μmφ, when the semiconductor laser is in multi-mode oscillation, an elliptical spot with a length corresponding to the number of modes is formed on the recording medium. be able to. In other words, when using a transmissive grating element in the optical system of an optical pickup device, an elliptical spot can be easily formed on the recording medium by making the oscillation axis mode of the semiconductor laser multiple. Ru.

Therefore, the same effect can be obtained even if diffracted light from a reflective grating element is used instead of a transmissive grating element. Further, 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. A light diffraction efficiency of 70 degrees or more can be achieved 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 a single mode and a multimode.

Two types of spots, circular and oval, are easily formed on the recording medium. In addition, methods for switching the oscillation axis mode of a semiconductor laser include a method in which a high-frequency current is superimposed on a laser that oscillates in a single mode by DC drive to make it multimode, and a method in which the electrodes of the semiconductor laser are divided in the resonator length direction. However, a method is available in which the number of oscillation modes is controlled by changing the ratio of currents applied to each electrode.

〔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, one embodiment includes a semiconductor laser l, a collimating lens 2, a grating element 3, a beam splitter 4, a condensing lens 5, a converging lens 7, a beam splitter 8, a track error detector 9;
a knife 10, a focus error detector 11,
DC circuit 12, high frequency circuit 13, and switching circuit 14.

It is configured to correspond to the recording medium 6.

Note that the DC circuit 12. High frequency circuit 13 and switching circuit 1
4ri forms a laser drive circuit that switches the oscillation axis mode of the semiconductor laser l.

In FIG. 1, the beam emitted from the semiconductor laser l is
The optical path is collimated by the collimating lens 2 and bent by the grating element 3.

It is sent to beam splitter 4. Furthermore, the light is focused as a spot on the recording medium 6 via the beam splitter 4 and the condensing lens 5. In this case, if the light emitting point is in the sheep-mode, a circular spot is formed, and if the light-emitting point is in the multi-mode, an oval spot is formed. The reflected light from the recording medium 6 passes through the beam splitter 4 and the converging lens 7 and enters the beam splitter 8, where it is separated and a portion is sent to the track error detector 9.
A portion of the light is incident on the focus error detector 11 via the knife lens 10. A spot position error from these reflected lights is detected.

In the configuration of this embodiment, d, grating element 3ri
It also has a beam shaping function that turns an elliptical beam into a circular shape. Note that the arrangement position hit of the grating element 3 may be set between the beam splitter 4 and the condenser lens 5. When recording and reproducing operations are performed, a predetermined circular spot +7) is formed on the recording medium 6 by driving the semiconductor laser l by the DC circuit 12 via direct current or low frequency, and when performing the erasing operation. To do this, a predetermined oval spot is formed on the recording medium 6 by driving the semiconductor laser l by superimposing the high-frequency current from the high-frequency circuit 13 on the self-current or low-frequency current through the connection control operation by the switching circuit 14. form.

〔Effect of the invention〕

As explained above, the present invention is capable of forming not only oval grooves and nine spots necessary for erasing, but also circular spots necessary for recording and reproduction on a recording medium with a relatively simple configuration. The present invention has the advantage that it is possible to provide an optical vibrator and a pickup device that can be used.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of an embodiment of the present invention.
FIG. 3 is a conceptual diagram of a transmission grating element used to demonstrate the effect of the present invention. 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 microscope device. . In the figure, 1.15... Semiconductor laser, 2゜16... Collimating lens, 3... Grating element, 4, 8.18... Beam splitter , 519...Condensing lens%6...
... Recording medium, 7... Converging lens, 9...
...Track error detector, 10...Knifetsuji, 11...Focus error detection -1'0
``i- device%12...DC circuit, 13...old high frequency circuit, 14...switching circuit, 17...cylindrical lens, 20...detection optics System. Figure 1

Claims (1)

[Claims] In an optical pickup device that includes 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 has a single oscillation axis mode depending on the driving state. A semiconductor laser that can be switched between mode and multimode, a laser drive circuit that switches the oscillation axis mode of the semiconductor laser, and a transmissive or reflective grating element between the semiconductor laser and the recording medium. An optical pickup device comprising: an optical path conversion element that utilizes diffracted light.