JPH01179235A - Information erasing device for optical information recorder - Google Patents

Abstract

PURPOSE:To facilitate design and adjustment by forming an elliptical laser spot by utilizing the large astigmatic difference of a gain waveguide type semiconductor laser, and adjusting the parameters of a collimator lens and an objective lens. CONSTITUTION:The adjustment of the collimator lens 2 is performed so as to set in parallel laser beams emitted from a light emitting point Px on a plane xz. At this time, the length of the laser spot in a direction of (x) converged on a recording medium 4 by the objective lens 3 goes to length l1 decided by the focal distance of the objective lens 3 and the diameter of an incident beam to the objective lens 3. Meanwhile, since a light emitting point Py on a plane yz is deviated by the astigmatic difference DELTAz from the light emitting point Px on the plane xz, the laser beam emitted from the collimator lens 2 is converged at the front of the recording medium 4, and the length of the laser spot in a direction of (y) goes to l. Thus, it is possible to perform the design and the adjustment easily by forming the elliptical laser spot with simple constitution by utilizing the large astigmatic difference DELTAz of the gain waveguide type semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an information erasing device for a rewritable optical information recording device, and more particularly to a device for forming an oval laser spot used when erasing information.

[Conventional technology]

In recent years, in optical information recording devices capable of high-density recording, a method of recording and erasing information using a phase change between a crystalline state and an amorphous state of a recording layer has been attracting attention. In this method, when erasing information recorded in the recording layer, the recording layer is changed from an amorphous state to a crystalline state, but this phase change requires a long time, so the surface of the recording layer In this case, an optical device is required that can obtain an oblong Radhe spot extending in the track direction of the recording layer. As an optical device for obtaining this elliptical laser spot, a device described in Japanese Patent Application Laid-open No. 160846/1984 is known.

FIG. 6 is a schematic configuration diagram showing the optical device described in the publication.

In the same figure (a), the laser beam emitted from the semiconductor laser 2I is made into a parallel beam by the collimating lens 22, then made into an elliptical beam with a large aspect ratio by the prism 25 for shape correction, and then converged by the objective lens 23. By doing so, an oval laser spot is formed on the recording medium 24.

In FIG. 4B, a slit 26 is used in place of the prism 25 in FIG.

In the same figure (C), the laser beam emitted from the semiconductor laser 21 is passed through a cylindrical lens 27.2 whose axial directions are orthogonal to each other.
8 to form a beam with an elongated cross-section.

In FIG. 6, an acousto-optic light modulator 29 is used in place of the prism 25 in FIG.

In the same figure (e), a cylindrical lens 30 is used in place of the prism 25 of the same figure (a), and the focal position after passing through the objective lens 23 in a direction not affected by the cylindrical lens 30 and a direction in which it is affected. By shifting the laser beam, an oval laser spot is formed on the recording medium 24.

[Problem that the invention seeks to solve]

However, these conventional optical devices each have the following problems.

In the apparatus shown in FIG. 6(a), since the optical axis of the optical system is bent by the prism 25, the design of the rA configuration is complicated and adjustment is difficult. In the device shown in FIG. 2(b), vignetting of the laser beam occurs due to the slit 26, so
Large light loss. In the apparatus shown in FIG. 2C, since two cylindrical lenses 27 and 28 with short focal lengths are used, adjustment is extremely difficult. In the device shown in FIG. 2D, the acousto-optic light modulator 29 has a large external shape and is expensive. Same figure (
In the device e), a cylindrical lens 30 with a very long focal length is used.
is required, making the device large and expensive.

It is an object of the present invention to solve these problems and form an oblong laser spot using an inexpensive device that is easy to design and adjust when erasing information from a rewritable optical information recording device.

[Means for solving problems]

In order to achieve the purpose, the information erasing device for an optical information recording device of the present invention includes a gain waveguide semiconductor laser and an optical system that focuses a laser beam emitted from the gain waveguide semiconductor laser onto a recording medium. It is characterized by becoming.

[Effect]

In the present invention, a gain waveguide semiconductor laser is used as a semiconductor laser for erasing information in an optical information recording device. In this gain waveguide semiconductor laser, the positions of the light emitting points in the direction perpendicular to the junction surface and the light emitting points in the parallel direction are significantly different. Therefore, when a laser beam emitted from this gain waveguide semiconductor laser is focused onto a recording medium by an optical system consisting of a lens, etc., it is focused in one direction on the surface of the recording medium, but it is focused in one direction on the surface of the recording medium, but the laser beam is focused in one direction on the surface of the recording medium, but the laser beam is Don't focus on direction. That is, an oblong Radespot is formed on the recording medium, making it suitable for erasing information in an optical information recording device.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a schematic diagram showing the basic configuration of an apparatus according to an embodiment of the present invention. The semiconductor I2 is a gain waveguide type semiconductor laser. Gain waveguide semiconductor lasers typically have a gain of 20 to 50
Although it has an astigmatism difference of about am, in this example, the astigmatism difference is about 40.1) A waveguide semiconductor laser was used.

The collimating lens 2 and the objective lens 3 are arranged so that the length of the long sleeve of the oval laser spot on the recording medium 4 is approximately 10 am (t).
A lens with a focal length of 7 mm and 4.3fffffl that satisfies the relational expression described later was used so that the following relationship was obtained: /e2 full width). The divergence angle of the laser used was 14 degrees (full width at half maximum).
Therefore, the laser beam diameter in equation (1), which will be described later, is 2.9 mm<1/e' (full width).

FIG. 2 is a schematic diagram for explaining the astigmatism difference of a semiconductor laser. The laser beam emitted from the laser chip 5 spreads and travels in the direction perpendicular to the bonding (X direction) and parallel direction (X direction) as shown in the figure, but its light emitting points PX and [)y are located as shown in the figure. are different. The distance between the light emitting points PX and I'y is called the astigmatism difference Δ2. This astigmatism difference ΔZ is small, about 5- or less, in semiconductor lasers with waveforms other than equal gain (for example, refractive index-guided semiconductor lasers), but in the case of gain-guided waveform semiconductor lasers, it is 20-50.
-It's a big deal. If the astigmatism difference ΔZ is large, when trying to make a parallel beam with a collimating lens, the
Either direction is not a parallel beam.

For this reason, in conventional optical recording devices that utilize parallel beams, refractive index waveguide semiconductor lasers with a small astigmatism difference ΔZ have been used exclusively.

In contrast, in this embodiment, by actively utilizing the large astigmatism difference ΔZ of the gain waveguide semiconductor laser,
A simple optical system is used to form an oval laser spot on a recording medium.

FIGS. 3(a), 3(b), and 3(c) are schematic diagrams for explaining a method of forming an oval laser spot. Same figure (
As shown in a), the collimating lens 2 is adjusted so that the laser beam emitted from the light emitting point PK in the xz plane becomes parallel. At this time, the length of the laser spot focused on the recording medium 4 by the objective lens 3 in the X direction is determined by the focal length of the objective lens 3 and the diameter of the beam incident on the objective lens 3! , becomes. - direction, the luminescent point py in the 72 plane is xz
Since it is shifted from the in-plane light emitting point Px by the astigmatism difference Δ2, the laser beam exiting the collimating lens 2 converges in front of the recording medium 4, as shown in υ in the same figure, and the laser beam on the recording medium 4 converges in front of the recording medium 4. The length of the laser spot in the X direction is l.

As a result, the cross-sectional shape of the laser spot 6 on the recording medium 4 becomes a vertically elongated oval, as shown in FIG. 4(C).

FIGS. 4(a), 4(b), and 4(c) are schematic diagrams for explaining a method of creating another oval laser spot 7). 7
By adjusting the collimating lens 2 so that the laser beams emitted from the light emitting points Py in two planes are parallel, the cross-sectional shape of the laser spot 6 on the recording medium 4 becomes a horizontally long cross-sectional shape as shown in FIG. It becomes an oval shape.

The length E of the long axis of the oblong Radespot obtained by the method described above can be calculated using geometrical optics. When calculated using Newton's well-known formula, the result can be approximated as follows. Here, ΔZ is the astigmatism difference, f, is the focal length of the collimating lens 2, r2 is the focal length of the objective lens 3, and D is the length of the laser beam spot in the plane forming the long sleeve at the emission position of the collimating lens 2. Diameter (
(See Figures 3 and 4).

From the above, the semiconductor laser 11 collimating lens 2
By adjusting each parameter of the objective lens 3 so as to satisfy the above formula (1), an oval laser spot of a desired size can be formed. Therefore, the design and adjustment of the optical system is easy, and the device has a simple configuration.

Furthermore, since the optical path length of the entire optical system is not included in equation (1), it is easy to design a separate optical head that can change the optical path length as an optical head for erasing information in an optical information recording device. becomes.

In the above embodiment, an optical system including a collimating lens and an objective lens was used as an optical system for focusing the laser beam emitted from a gain waveguide semiconductor laser onto a recording medium, but an optical system with only an objective lens was used. It may be a system. In this case, as shown in Figure 5, the length of the long sleeve of the oval laser spot is determined by the focal length of the objective lens.
is determined, and an oval laser spot is obtained at the position indicated by reference numeral 7 or 8.

〔Effect of the invention〕

As explained above, in the present invention, the large astigmatism difference of a gain-guided semiconductor laser is actively utilized,
By adjusting the parameters of the collimating lens and the objective lens, an information erasing device that forms an oval laser spot can be obtained with a simple configuration. The information erasing device of the present invention has a small number of parts and is easy to design and adjust.
It also has the advantage of being inexpensive and having little optical loss.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the basic configuration of an embodiment device of the present invention;
Figure 2 is a schematic diagram for explaining the astigmatism difference of a semiconductor laser, Figures 3(a) to (C), and Figures 4(a) to (C).
) and FIG. 5 are schematic diagrams for explaining the method of forming an elliptical laser spot, and FIG. 6 is a configuration diagram showing a conventional elliptical laser spot forming apparatus. l: Gain waveguide semiconductor laser 2.22: Collimating lens 3.23: Objective lens 4
．． 24: Recording medium 5: Laser chip 6: Laser spot T, 8: Formation position of oblong Radespot 21: Semiconductor laser 25 Nibrism 26: Slit
27.2g, 30: cylinder 1, lens 29: Onken optical light change 1 penalty PX, py: luminous point Δ2: astigmatic difference patent applicant Fuji Xerox Co., Ltd. agent
Masu Kobori (and 2 others) lol 1 Sa 3rd figure (b) 4th figure rod 5 [-'

Claims (1)

[Claims] 1. An information erasing device for an optical information recording device, comprising a gain waveguide semiconductor laser and an optical system that focuses a laser beam emitted from the gain waveguide semiconductor laser onto a recording medium.