JPS6087441A - Optical device for optical disk - Google Patents

Abstract

PURPOSE:To form easily both recording and erasing light spots by putting a cylindrical lens, a linear grating or a prism into a laser luminous flux and then taking them out of the luminous flux to change the size of the light spot. CONSTITUTION:The light irradiated from a semiconductor laser 1 is converted into parallel beams through a coupling lens 2, and an oval pattern 7 is obtained for the light intensity distribution on sections of said parallel beams. A cylindrical lens 3 is set into a non-focus system fo convert the pattern 7 into a circular pattern 8. The laser light converted into a circular pattern is stopped down to a minute circular light spot on an optical disk 6. Then the laser recording is carried out. In an earsion mode a stage 10 is moved by a motor 9 and the lens 3 is taken out of an optical path. Then a light spot for erasion is obtained on the disk 6 in response to the pattern 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical device for an optical disc when a laser-recordable and laser-erasable material is used as the optical disc medium.

[Background of the invention]

Chalcogenide compounds are examples of materials that can be recorded and erased by laser. In this material, it is possible to reversibly transition from a crystalline state to an amorphous state or vice versa using laser light.

In other words, by irradiating a material with high power laser light for a short time, it is possible to transform the material from a crystalline state to an amorphous state, whereas by irradiating a material with a low laser power for a long time to an amorphous state, It is possible to return from an amorphous state to a crystalline state.

FIG. 1 shows an enlarged view of the recording formed on the material. Recorded information is recorded at small points with different reflectances along the track. Usually the track pitch is 1.6
It is about μm. The recorded information is in an amorphous state.

In order to form such recorded information, a minute laser beam spot with a diameter of about 1.0 μmφ as shown in FIG. 1(b) is used.

On the other hand, when erasing recorded information, it is necessary to irradiate laser light for a long time with a lower laser power than when recording. To achieve this, the erasing laser beam spot is shown in Figure 1 (C
), it is formed long in the track direction. In other words, since the erasing laser beam spot has a larger shape than the recording spot, the laser power per unit area is weaker, and since the spot is long in the track direction, it takes a long time to reach the information you want to erase. This means that the laser beam is irradiated for a certain period of time.

[Purpose of the invention]

An object of the present invention is to provide a single optical device that can easily realize the above-described recording light spot and erasing light spot.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention includes a cylindrical lens, a one-dimensional grating, or a flashlight in a laser beam.Embodiments of the Invention A detailed explanation will be given below with reference to embodiments.

FIG. 2 shows an optical device of the invention. The light from the semiconductor laser 1 has an elliptical anisotropic emission radiation pattern as shown in FIG. Therefore, in FIG. 2, the light emitted from the semiconductor laser is transferred to the coupling lens 2.
Converts to parallel light. The cross-sectional light intensity distribution of the converted parallel light has an elliptical pattern as shown in 7. In order to convert such an elliptical pattern into a circular pattern 8, a cylindrical lens 3 arranged in an afocal system is arranged. The laser beam in a circular pattern is guided to an objective lens 5 via a reflection mirror 4, and is directed to an optical disk 6.
Laser recording is performed by focusing the light into a minute circular light spot as shown in FIG. 1(b). When erasing, the stage 10f on which the cylindrical lens is mounted is moved by the motor 9 so that the cylindrical lens comes out of the optical path. An erasing light spot is obtained on the disk 6. Second
In the figure, a motor is used to move the cylindrical lens, but an element that applies electromagnetic force or piezoelectric force, such as a solenoid coil, may also be used. Furthermore, although a cylindrical lens is used in FIG. 2, other anamorphic optical systems such as a prism may also be used.

FIG. 4 shows an example in which a one-dimensional grating is used instead of the cylindrical lens shown in FIG. Since the laser light emitted from the coupling lens has an elliptical light pattern similar to that shown in FIG. 2, it is converted into a circular pattern by the prism 11.

The laser beam converted into a circular shape passes through the one-dimensional grating 12. The laser light that passed through the -dimensional grating is the 0th-order diffracted light and the +1st-order diffracted light.

-The first-order diffracted light is guided by the object tape lens,
It is focused on an optical disk. Figure 5 shows a one-dimensional grid 12
1(C) is used to explain the principle of forming a light spot as shown in FIG. 1(C). Assume that the -dimensional grating has a refractive index n and a thickness d that changes sinusoidally. That is, in Fig. 2π5(a), d = d6 +d1stn (
-x). In this case, the phase t of the amplitude transmittance is given by the following equation.

dO + dl *p see Figure 5, λ is the wavelength of light.

Equation (1) can be expressed as the following equation.

, 2π 2π t = exp s −nd(1Σ t J n (
2ndl) λ n yaw.

Φexp(in2π-)00°-(2) In equation (2), the n term is a term related to the n-th order diffraction wave, and causes the n-th order precipitated liquid of the incident laser beam. The light intensity of the n-th precipitation solution is Jn”
(Tndl).

It is best to set it close. n = 1.5, λ = 0.63
If it is 3X10-3, then d1=9.36X10-' fog.

With this setting, as shown in FIG.
Only the next and +1st order laser beams are focused by the objective lens.

The focal length of the objective lens is f, which is the aperture.

FIG. 5(b) shows the shape of the spot focused on the optical disk. An elongated spot can be obtained using the θ-order light and the ±1st-order light.

Although FIG. 5 shows an example using a sine wave grating, a triangular wave grating or a rectangular grating may also be used.

Although FIG. 5 shows an example in which a single sinusoidal grating is used, it is clear that a longer light spot in one direction can be obtained by arranging a plurality of gratings along the optical axis.

[Brief explanation of the drawing]

FIG. 1(a) is a diagram illustrating recording information formed on an optical disc, FIG. 1(b) is a diagram showing the shape of a recording spot focused on the disc, and FIG. FIG. 2 is a diagram showing the shape of the erasing light spot, FIG. 2 is a diagram of an optical disk optical device showing an embodiment of the present invention, FIG. 3 is a diagram explaining the laser beam radiation distribution of a semiconductor laser, and FIG. 4 is a diagram showing the embodiment of the present invention. A diagram of an optical device for an optical disk showing another embodiment, FIG. 5(a),
(b) is a diagram illustrating the operating principle of the optical device for optical discs of the present invention.

Claims (1)

[Claims] 1. In an optical disk optical device that records and erases information on a disk using laser light, the disk is placed by inserting and removing a cylindrical lens, one-dimensional grating, or prism into the laser beam.