JPS61184737A - Multibeam optical pickup device - Google Patents

Abstract

PURPOSE:To form two kinds of different spots by forming a semiconductor laser which has plural luminous points and in which the width of the active laser contributing to the light emission of at least one luminous point is larger than the width of the active layer contributing to the light emission of the other luminous point and the luminous points are so formed as to permit independent driving. CONSTITUTION:An n-Al0.4Ga0.6As layer 2 up to a p-GaAs layer 7 are successively formed on an n-GaAs substrate 1 and thereafter the layers are subjected to mesa-etching down to the substrate 1 to form plural pieces of belt-like mesa- regions having the active layer. The width of the active layer is changed by the mesa width in this stage. The layer 5 and the active layers 4a, 4b are etched to provide contraction 8. A p-Alo.4Ga0.6As layer 9, a p-Al0.3Ga0.7As layer 10 and an n-Al0.4Ga0.6As layer 11 are successively formed so as to embed the side faces of the mesa regions. A diffused region 12, a p-ohmic electrode 13 and an n-ohmic electrode 14 are then formed by Zn diffusion and the p-ohmic electrode 13 is separated between the respective lasers by chemical etching, by which the independent driving of the respective lasers is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-beam optical pickup device suitable for an optical information recording device that records, reproduces and erases information by irradiating light.

[Prior art and its problems]

BACKGROUND ART There are media that use phase change between polycrystalline and amorphous states to record information through light irradiation. Examples of the material include Te-0-Ge-3n metal type and To-3e-3n alloy type. The characteristics of these materials are:
When a material is subjected to temperature changes, it becomes amorphous if it is rapidly heated or rapidly cooled, and crystallized if it is heated or cooled relatively slowly. When the phase changes, the reflectance of the surface also changes, so the state of the phase can be determined by irradiating it with weak light. Using this phase change, information can be recorded, reproduced, and erased.

As a method of realizing both phase changes from crystal to amorphous and from amorphous to crystal within one track width in the shape of an optical disk, as shown in FIG. 6, the spot shape irradiated onto the recording medium 6o by the optical pickup device is circular. There is a method of forming two types of spots 61 on the trunk 63, and spots 62 that are oval in the track direction. If the relative speed between the recording medium and the optical pickup device is constant, high power irradiation at the circular spot 61 will rapidly heat and cool the recording medium, and relatively low power irradiation at the oval spot 62 will remove heat. , slow cooling can be performed. Formation of information pits by circular spots 61 and oval spots 62
By erasing, information can be recorded for each track width,
erasure can be achieved.

Forming such two types of spots with different optical pickup devices would complicate the entire device, so it is desirable to be able to form two types of spots with the same optical pickup device.

As a method of configuring an optical pink-up device that forms two different types of spots, for example, there is a method of using two semiconductor lasers with different wavelengths and inserting a cylindrical lens or the like into one optical system to form an elliptical spot. 7th
The figure shows a pickup device using this method. In the figure, 71° and 72 are semiconductor lasers with different wavelengths, 73.
74 is a collimating lens, 75 is a cylindrical lens, 76 is a polarizing beam splinter, 77.78 is an A wavelength plate, 79 is a condensing lens, 80 is a wavelength filter, 81 is a detection optical system, and 60 is a recording medium. This pink-up device has disadvantages in that the positional relationship between the two spots on the recording medium 60 depends on the mechanical stability of the optical system, so it is unstable with respect to temperature changes, etc., and the optical system is also complicated. There is.

As another method for configuring an optical pickup device that forms two different types of spots, a method has also been proposed in which an AO modulator is inserted into the collimated light and a plurality of frequency components are applied to the AO modulator to form an elliptical spot. ing. However, even in a multi-beam optical pickup device using this method, the optical system inevitably becomes complicated.

[Purpose of the invention]

An object of the present invention is to provide a multi-beam optical pickup device that can form two different types of spots without complicating the optical system as described above.

[Structure of the Invention] The multi-beam optical pickup device of the present invention includes a light source having a plurality of light emitting points, a photodetector, and irradiates light emitted from the light source onto a recording medium as a minute spot to collect information from the recording medium. an optical system that guides light contained in the light to the photodetector, the light source having a plurality of light-emitting points on the same substrate, and an active device that contributes to light emission of at least one light-emitting point. The semiconductor laser is characterized in that the width of the layer is larger than the width of the active layer that contributes to light emission from other light emitting points, and that each light emitting point can be driven independently.

〔Example〕

FIG. 1 shows an example of a semiconductor laser used as a light source in an embodiment of the optical pickup device of the present invention. This semiconductor laser has a structure that has two active layers with the same thickness but different widths, and a semiconductor laser with this structure can be easily manufactured using conventional buried laser manufacturing technology. can. By the first liquid phase crystal growth method, n
- Sequentially n A l O, 4G a on GaAs substrate 1
(1,6A s layer 2, n -A 1! (3,3G
a O,? A s layer 3, A J o, which becomes an active layer.

GaO,9A s layer 4a, 4b, p-
A I20.6 Ga (14A 5 layers 5, p A
l (14G a □, 6A 3 layer 6, p-GaAs
Form layer 7. Thereafter, mesa etching is performed by chemical etching until it reaches the substrate 1, thereby forming a plurality of band-shaped mesa regions having active layers. The width of the active layer can be changed depending on the mesa width at this time. Next, layer 5 and active layer 4a are formed by etching.

4b to form a constriction 8. Next, in a second crystal growth process, as shown in FIG. 1, I) AgCL4Ga0. SAa layer 9
, 1) -A I (1,3G ao, 7A s layer 10. n-Aj!α4G a O, 6A s layer 11 is formed in sequence. The layer 10 is placed under the active layer by the previously formed constriction 8. Thereafter, the diffusion region 12, p-ohmic electrode 13, and n-ohmic electrode 14 are formed by Zn diffusion, and the p-ohmic electrode 13 is separated between each laser by chemical etching. can be driven independently.

The semiconductor laser used in the present invention can be formed in the manner described above. The active layers 4a and 4b can be easily formed if the width is 1 μm or more. For example, if the ratio of the lengths of the spots on the recording medium is 1=3, the shape of the laser light emitting point is approximately proportional to the width of the active layer, so the width of one active layer 4a is 1 μm, The other active layer 4b
The width may be set to about 3 to 4 μm.

Although the above embodiments have been described with respect to a buried type semiconductor laser, the present invention can also be practiced with other laser structures such as an internal stripe type or a narrow stripe type. However, in lasers other than buried-type lasers, the active layer exists over the entire substrate, and it is necessary to determine the light emitting region by limiting the current injection region. Therefore, in this case, the width of the current injection region can be considered as the width of the active layer.

FIG. 2 shows an optical system having a semiconductor laser as shown in FIG. 1 as a light source. In the figure, 21 is a laser light source, 22 is a collimating lens, 23 is a polarizing beam splitter, 24 is an A wavelength plate, 25 is a condenser lens, 26 is a detection optical system, and 27 is a recording medium.

The emitted light from the laser light source 21 is passed through a collimating lens 22.
Polarizing beam splitter 23. The light is focused onto the recording medium 27 by the condensing lens 25 via the gas-liquid long plate 24 . Since the laser shown in FIG. 1 is used as a light source, an image of the light emitting point of the light source is formed on the recording medium 27, and as a result, a circular spot 61 and an oval spot 62 are tracked as shown in FIG. 63.

Since the reflected light from the recording medium 27 undergoes polarization rotation at the A wavelength plate 24, it is reflected by the polarization beam splinter 23 and guided to the detection optical system 26. In the detection optical system 26, focus error, tracking error detection, and reproduction signal detection are performed. For error detection, the Knifezi method or far field method used in conventional optical pickup devices can be used. However, since the reflected light is formed from multiple beams, it is necessary to take measures such as forming an image with a lens and then separating only the necessary beams with a pinhole or slit.

As described above, by using a semiconductor laser having two light emitting points, it is possible to realize an optical pick amplifier device that can easily form circular and oval spots on a recording medium using almost the same optical system as for conventional DRAW. be able to.

Such optical pink amplifier device can drive circular and oval spots independently. circular spot 61
is used for recording and reproducing information, and the oval spot 62 is used for erasing information. Possible uses of these spots include recording immediately after erasing and erasing immediately after reproduction.

FIG. 3 is a diagram showing another example of the optical system. If the dimensions of the light emitting point of the light source are significantly different in the thickness direction and the width direction, correction may be made using a shaping prism 30 or the like so that the focused spot becomes circular, but in this case as well, two light emitting points are used. Since the relationship between the size of the dots is preserved, circular and oval spots can be formed on the recording medium. In the figure, the same elements as in FIG. 2 are denoted by the same numbers.

Although the optical system shown in FIGS. 2 and 3 uses reflected light from a recording medium as information-containing light, it is clear that a structure that uses transmitted light from a recording medium may also be used.

FIG. 4 shows another example of a semiconductor laser used as a light source. This semiconductor laser has three light emitting points, including an active layer 41 with a width of about 1 μm and an active layer 41 with a width of 3 to 4 μm.
An active layer 42 with a width of about 1 μm and an active layer 43 with a width of about 1 μm.
It is equipped with Note that this semiconductor laser can be manufactured in the same manner as the semiconductor laser shown in FIG. 1, and the same elements are given the same numbers as in FIG. 1.

If such a semiconductor laser is used, each active layer 41.4
The emitted light from 2.43 is a circular beam spot 51.2 as shown in FIG. 5(a). An oval beam spot 521 and a circular beam spot 53 can be focused on the recording medium. When the slot is moving in the direction of the arrow with respect to the recording medium, the state of the recording medium can be checked at spot 51, erased at spot 52, and new information can be recorded at spot 53. can. If the structure of the semiconductor laser is changed, it is possible to form a spot as shown in FIG. It is also possible to implement a function of checking.

Although the present invention has been described in detail above, the present invention is not limited to these embodiments, and it goes without saying that various modifications and changes can be made within the scope of the present invention.

〔Effect of the invention〕

As described above, according to the multi-beam optical pickup device of the present invention, beam spots of different shapes can be formed on a recording medium without using a complicated and unstable optical system.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of a semiconductor laser used in an embodiment of the present invention, Fig. 2 is a diagram showing an example of an optical system in an embodiment of the invention, and Fig. 3 is a diagram showing another example of the optical system. 4 is a diagram showing another example of a semiconductor laser, FIGS. 5 and 6 are diagrams showing beam spot shapes, and FIG. 7 is a diagram showing an optical pickup device according to the prior art. 1...n-GaAs substrate 2, 11...n Aj! (1,4GaO,6A
s-layer 3 Hata 1 Takinaka 1・n-Alo, 3 Gao, 7 AswI
4 a, 4 b...Aj! (1, IGa□, 43
AS active layer 5 ” ” pAAO, 6GaO, 4A
3 layers 6, 9... p-Al (14GaO, 6As
Layer 7... p-GaAs layer 8... constriction 10 '''' p Alo, 3Ga (4,7AS
Layer 12... Zn diffusion region 13... P-ohmic electrode 14... N-ohmic electrode 21... Light source 22... Collimating lens 23...・Polarizing beam splitter 24...A wavelength plate 25...Condensing lens 26...Detection optical system 27...Recording medium 51.53, 55.56...Circular Spot 52, 54... Oval spot 30... Shaping prism

Claims (1)

[Claims] (1) A light source having a plurality of light emitting points, a photodetector, and an optical system that irradiates a recording medium with light emitted from the light source as a minute spot and guides light containing information from the recording medium to the photodetector. A multi-beam optical pickup device comprising: the light source having a plurality of light emitting points on the same substrate;
The width of the active layer that contributes to light emission from at least one light-emitting point is larger than the width of the active layer that contributes to light emission from other light-emitting points,
A multi-beam optical pickup device, further comprising a semiconductor laser formed so that each light emitting point can be driven independently.