JPS63269133A - Light source for optical pickup - Google Patents

Abstract

PURPOSE:To allow one spot to read out a bit recorded or erased by the other spot by forming a light source consisting of one or more semiconductor lasers and one or more nonlinear optical device on the same substrate. CONSTITUTION:The light source consisting of semiconductor lasers and nonlinear optical device for converting light radiated from the lasers into higher harmonic is formed on the same substrate. For instance, two lasers 101, 102 and one nonlinear optical device 104 are formed on the same substrate 103 to form spots with different wavelengths on a disk by means of one optical system. Since the wavelengths of these spots are sharply different, mutual interference is not easily generated, these spots can be simultaneously used and a recorded bit can be read out immediately after the recording. In addition, a bit with accurate size can be formed by properly using one spot for writing and the other for focusing and tracking at the time of recording.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a light source for an optical pickup used for recording and reproducing optical discs.

2. Description of the Related Art In recent years, optical discs such as compact discs have become rapidly popular due to their high recording density and lower system costs. To record information on an optical disk, a high-power laser for writing or erasing and a low-noise laser for reading are required. A semiconductor laser integrated on a chip semiconductor substrate is used. An example of a semiconductor laser for an optical pickup used in a conventional optical disc will be described below with reference to the drawings.

Figure 6 shows Ga used in a conventional optical pickup.
As/Al, -! 1 is a configuration diagram of a double heterojunction semiconductor laser using Ga and As, which is integrated on a GaAs substrate. FIG.

The semiconductor laser 601 is a high-output type, can obtain an optical output of about 30 mW, and is mainly used when recording information on an optical disk. The semiconductor laser 602 has an output of about 3 mW, but is a low noise type with a relative noise intensity of 1140 dB or less, and is mainly used when reading information from a disk. By forming these two lasers on the same GaAs substrate 603 and using the lasers separately during recording and reproduction, a stable bit size can be achieved during recording compared to when recording and reproducing with a single laser. This means that a signal can be obtained with low noise during readout (for example, M, Kume; IEEE Journal OpQuantum Electronics-21 (M, Kume; IEEE T, QE).
-21), 707 (1985)).

Problems to be Solved by the Invention However, with the above configuration, reading cannot be performed when writing, and writing cannot be performed when reading. However, in order to record information at a higher density and write and read more quickly and efficiently, it is necessary to have each laser work independently at the same time, but in the case of conventional methods, the following problems arise: It had

(1) In the conventional example, the reading and writing lasers are GaAs/A 1,-xGa! Since they have similar structures of As, their respective oscillation wavelengths are very close to each other around 860 nm. For this reason, it is difficult to use them simultaneously due to problems such as mutual interference of each other's lights. In particular, low noise characteristics are required during reading, but the writing light of Takayama Katsui Power generates a large amount of noise.

(@ Since each laser cannot be driven at the same time, writing is performed while focusing with the writing laser, so the 7-o-cutting during writing is unstable, so the bit size is not constant. Therefore, when writing There was a limit to the accuracy of information, and the density of information could not be improved.

In view of the above problems, the present invention provides a light source for an optical pickup that can perform writing and reading at the same time, or write while focusing with the other laser.

Means for Solving the Problems - In order to solve the above problems, the present invention provides one or more semiconductor lasers and one or more nonlinear optical elements that convert light emitted from the semiconductor lasers into harmonics. The present invention is to use a light source for an optical pickup in which a light source consisting of ZnSe crystal, ZnSe crystal,
The method is to employ a light source for an optical pickup made of a ZnS crystal, a mixed crystal of ZnSe and ZnS, or a laminated structure of these.

Function: With this configuration of the present invention, bits recorded or erased at one spot can be read at the other spot while using the same optical system.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a configuration diagram of a light source for an optical pickup according to this embodiment, in which 101 and 102 are semiconductor lasers, 103 is a substrate, and 10
4 is a nonlinear optical element. The semiconductor laser 101 is a high-output type, has an oscillation wavelength of 840 nm, and is mainly used when recording information on an optical disk. 102 is the same as 1o1,
Although it is a high output type and has an oscillation wavelength of 850 nm, the light emitted from 102 is incident on a nonlinear optical element. The nonlinear optical element 104 converts the light emitted from the semiconductor laser 102 into a second harmonic wave 106 having a wavelength of about 4215 nm. By forming the two lasers and nonlinear optical elements as described above on the same substrate 103, spots with different wavelengths can be formed on the disk using one optical system. Therefore, since the wavelengths of these spots are greatly different, mutual interference is less likely to occur, and they can be used simultaneously. Therefore, it is possible to read the recorded bits immediately after recording, and by using one side exclusively for writing and the other for focusing and tracking during recording, it is possible to form bits of accurate size.

FIG. 2 is a configuration diagram of an optical pickup using the present optical pickup light source. In the figure, 206 is a long wavelength cut filter, 207 is a polarizing beam splitter (hereinafter P
BS), 208 is a λ/4 plate, 209 is a focusing lens, 210 is a focusing and tracking coil, 211 is a cylindrical lens, 212 is a half mirror, 1213 is a long wavelength cut filter, and 216 is a short wavelength cut filter. , 214, 216 are photodetectors (
(hereinafter abbreviated as PD), 217 is an amplifier, and 218 is an optical disk. In addition, in the same figure, 101 to 104 are the first
It is the same as the picture.

The operation of the optical pickup configured as described above will be explained below with reference to FIG. 2. In FIG. 2, when recording information on the optical disc 218, a semiconductor laser 1o1 is used. The light emitted from the semiconductor laser 101 is P
Passing through the BS 207 and the λ/4 plate 208, the condensing lens 2
The light is focused on the disk 218 at 09. This condensing lens 209 is designed to have no aberration at both the semiconductor laser wavelength of 850 nm and its second harmonic wavelength of 425 nm, and to focus at the same position.

A part of the light focused on the disk is reflected, passes through the λ/4 plate 208 again, the optical path is bent by 90 degrees at the PBS 207, and then the light passes through the cylindrical lens 211 and the half mirror 2.
12, the light passes through a short wavelength cut filter 216 (cuts the second harmonic and passes only the first order light) and enters the PD 216. In the PD 216, a 7-occasion error signal is extracted using the astigmatism method, and a tracking error signal is extracted using the push-pull method.
is fed back to move the condenser lens 209 to control focus and tracking.

On the other hand, the light emitted from the nonlinear optical element 104 is filtered through a long wavelength cut filter 2 disposed near the nonlinear optical element 104.
06, the primary light is cut, and only the secondary light is separated. This secondary light passes through the same path as the emitted light of the semiconductor laser 1, is focused on the disk, is modulated by the pits on the disk, and is sent to the λ/4 plate 208, PBS 209, cylindrical lens 211, half mirror 212, and long The light passes through the wavelength cut filter 213 (cuts the first-order light and passes only the second-order harmonic) and enters the PD 214, where the signal is read. With the above-described configuration, the present invention uses light of different wavelengths as a light source, so it is easy to separate the writing and reading lights, and even if they are written and read at the same time, they do not affect each other. Furthermore, while focusing with one laser, writing can be performed with high precision using the other laser. Further, although the above explanation is limited to writing and reading, the same effect can be obtained by any combination of reading and erasing or erasing and writing.

The light source for an optical pickup according to the second embodiment of the present invention is
This will be explained using figures. Fig. 3 is a perspective view of a light source for an optical pickup, in which 101° and 102 are GaAs.
/A l 1-xGaJs double heterojunction semiconductor laser, 103 is a GaAs substrate, and 104 is a nonlinear optical element using ZnSe.

The semiconductor laser 101 is a high-power type, and the oscillation wavelength is 84.
0 nm and is mainly used when recording information on optical discs. Like 101, 102 is also a high-output type, and its oscillation wavelength is approximately the same at 850 nm, but the light emitted from 102 is incident on a nonlinear optical element, that is, Ze8e crystal 104. An optical waveguide 301 is formed in the nonlinear optical element 104, and the refractive index is controlled by an electrode 302. This nonlinear optical element 104 can generate a second harmonic wave 303 of about 425 nm by controlling the temperature within a certain range and changing the refractive index by applying a voltage to the electrode 301. By forming the two lasers and nonlinear optical elements as described above on the same substrate 103, spots with different wavelengths can be formed on the disk using one optical system. Therefore, since the wavelengths of these spots are greatly different, mutual interference is less likely to occur, and they can be used simultaneously. Therefore, it is possible to read the recorded pits immediately after recording, and by using one side exclusively for writing and the other for focusing and tracking during recording, it is possible to form pits of accurate size.

A method of manufacturing a light source for an optical pickup according to the first embodiment of the present invention will be briefly described with reference to FIG. In addition, in this explanation, for the sake of simplicity, the semiconductor laser 10 shown in FIG. 3 will be used.
2 and the nonlinear optical element 104 are formed on the same substrate.

On an n-type GaAs (001) substrate 103, n-type Al! is grown by liquid phase epitaxial growth (LPE). Ga...
A first cladding layer 401 of As (x = 0.3),
N-type GaAs active layer 402, P-type A 1yGa, -4
A second cladding layer 403 of s (y=O-3) and a contact layer 404 of p+ type GaAs were grown in sequence. Next, etching is performed using a dry etching technique using 5102 or photoresist or the like as a mask material 40e5 until reaching the first cladding layer 401, and each of the growth layers 401 to 4
Remove one half of 040. The plane direction of the step portion that occurs at this time was set to be (011). A third cladding layer 406 of Zn8 and a Zn5Ss
An optical waveguide 407 and a fourth cladding layer 408 of ZnS were sequentially grown by the MOVPE method.

Here, the height of the interface between the active layer 402 and the second cladding layer 403 from the substrate 103 and the height of the interface between the optical waveguide 407 and the fourth cladding layer 408 from the substrate 103 are the same height. I grew up like that.

Next, remove the 8i02405 and rewrite (011)
After forming 5102 stripes extending in the direction, etching was performed to a depth reaching a part of the first cladding layer 401 using this as a mask material to form optical waveguide stripes in the laser section and the SHG.

Furthermore, after forming 5IO2409 on the SHG optical waveguide section, a buried layer 410 was grown again from high-resistance AlGaAs in the part of the laser section where the crystal had been removed by etching. Also, the metal electrode 30 on the SHG element
2 was selectively formed by commonly known vapor deposition and etching methods.

A light source for an optical pickup according to a third embodiment of the present invention will be described with reference to FIG. In FIG. 6, 101 to 104 are the same as those in FIG. 3. The difference from the configuration shown in FIG. 3 is that a nonlinear optical element 601 is provided.

In the figure, the nonlinear optical element 601 is the nonlinear optical element 1.
By adopting the same structure as 04 and controlling the refractive index with the electrode 503, the emitted light of the semiconductor laser 1o1 is
It can be converted to the next harmonic.

Further, it is also possible to directly output the primary light from the optical waveguide 502 on the nonlinear optical element 601 without converting the primary light into secondary light using the electrode 1503. Therefore, one of the nonlinear optical elements 104 and e501 can be used for primary light, and the other can be used for secondary light.

As described above, by newly providing the nonlinear optical element 601, by simply changing the voltage applied to the nonlinear optical element, one can be used as primary light and the other as secondary light, or both can be used as primary or secondary light. This means that it can be used in different ways, including conventional examples.

Although the above embodiments are limited to writing and reading, any combination of reading and erasing or erasing and writing can be used without changing the configuration.

Effects of the Invention As described above, according to the present invention, pits recorded or erased in one spot can be read in the other spot while using the same optical system. In other words, by monitoring information while it is being recorded on the disc, recording errors can be corrected immediately and the correct data can be re-recorded, and erasing errors can be prevented by monitoring whether the information on the disc has been erased. You will be able to do this. Furthermore, since it is possible to write with one laser while focusing with the other laser, it is possible to form pits of accurate size on the disk.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a light source for an optical pickup according to a first embodiment of the present invention, FIG. 2 is a configuration diagram of an optical pickup using the first embodiment, and FIG. 3 is a diagram showing a second embodiment of the present invention. A perspective view of a light source for an optical pickup in the example, FIG. 4 is an explanatory diagram showing a method of manufacturing the light source for an optical pickup of the first example,
FIG. 6 is a perspective view of a light source for an optical pickup according to a third embodiment of the present invention, and FIG. 6 is a perspective view of a semiconductor laser used in a conventional optical pickup. 101.102... Semiconductor laser, 1o3...
...GaAs substrate, 104...Nonlinear optical element, 106...Laser light, 106...
・Second harmonic, 207...Polarizing beam splitter, 208...λ/4 plate, 209...
Condenser lens, 210... Focusing and tracking coil, 211... Cylindrical lens, 212... Half mirror 121
3...Long wavelength cut filter, 216...
・・Short wavelength cut filter, 214, 216・・・・
・Photodetector, 217...Amplifier, 21
8... Optical disk, 301... Optical waveguide, 302... Electrode, 4o 1.40 s-.
-・AlGaAm, 402,404... --GaAs,
406.408---ZnS1407...Zn
SSe, 501...Nonlinear optical element, 60
2... Optical waveguide, 603... Metal electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure 4 Figure 5 Figure 6

Claims (2)

[Claims] (1) A light source for an optical pickup, in which a semiconductor laser and a light source made of a nonlinear optical element that converts light emitted from the semiconductor laser into harmonics are formed on the same substrate. (2) Nonlinear optical element is ZnSe crystal, ZnS crystal, Z
The light source for an optical pickup according to claim 1, comprising a mixed crystal of nSe and ZnS, or a laminated structure thereof.