JPH03183032A - Semiconductor light emitter - Google Patents

Abstract

PURPOSE:To improve an S/N even when reading stored information from a recording carrier with a low light emitting output by providing plural laser chips, each different in reflectance on a laser emitting surface, and a hologram diffraction grating. CONSTITUTION:A laser beam, which is emitted from a semiconductor laser chip 11 for write at a high output, is made incident to a hologram diffraction grating 13. The 0th order beam transmitted through a hologram 13a is made incident to a recording carrier 17 and data are written into the carrier 17. Next, the laser beam emitted from a semiconductor laser chip 12 for read at a low output is made incident to the carrier 17. The 1st beam diffracted by the hologram 13a is made incident to the carrier 17. In the case of such operation, since the reflectance on the laser emitting surface of the chip 12 is made higher than the reflectance on the laser emitting surface of the chip 11, the returned beam to be reflected by the carrier 17 and to arrive at the chip 12 scarcely go into the internal part of the laser chip. Therefore, even when the light emitting output of the chip 12 is low, the data can be read out with high S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a semiconductor light emitting device used for optical pickup.

<Prior Art> Conventionally, an optical pickup has generally been configured as shown in FIG. This optical pickup includes one semiconductor laser chip 21, a beam splitter 22, a collimating lens 23, an objective lens 24, and a light receiving element 26. The laser beam output from the laser chip 21 is transmitted through a beam splitter 22, a collimating lens 23, and an objective lens 2.
4 and enters the record carrier 25. Then, writing is performed on the record carrier 25, or
is modulated (read) by the recorded information. Thereafter, the laser beam is reflected by the record carrier 25 and again by the objective lens 24. The light passes through the collimating lens 23 and enters the beam splitter 22, is further reflected by the beam splitter 22, and enters the light receiving element 26. Based on the signal output by the light receiving element 26 upon receiving this laser beam, a processing circuit (not shown) generates a servo signal for accurately tracking the track of the record carrier 25 and a reproduction signal (RF multiplied signal) representing the content of the recorded information. When writing to the record carrier 25, the light emitting output of the semiconductor laser chip 21 is increased to irradiate a strong laser beam, while when reading recorded information from the record carrier 25, This is done by lowering the light emitting output of the semiconductor laser chip 21 and irradiating it with weak laser light.Then, in order to cause the semiconductor laser chip 21 to emit light with high power during writing, as shown in FIG. Laser chip 2
An AR (anti-reflection) coating 31 is applied to the front surface (laser emission surface) 20 side of the laser beam 1 to lower the reflectance, while a high reflection coating 32 is applied to the rear surface 30 side to increase the reflectance, thereby increasing the light emission output. is set to be high.

<Problems to be Solved by the Invention> By the way, a portion of the laser light that is reflected by the record carrier 25, passes through the objective lens 24 and the collimating lens 23, and enters the beam splitter 22. The light then enters the laser chip 2I as so-called return light.

As is generally known, the laser chip 21 is excited by this returned light, and its light emission output fluctuates. Here, since the semiconductor laser chip 21 has a low reflectance on the front surface (laser emission surface) 31 side, a large amount of the return light from the record carrier 25 enters into the chip, which causes an induced output fluctuation (noise). ) is getting larger. Therefore, when reading stored information from the record carrier 25 with low light emission output, there is a problem that the S/N ratio deteriorates due to the return light noise caused by the return light.

Therefore, an object of the present invention is to be able to be used as a high-output light source for writing in an optical pickup, and also to increase the S/N ratio when reading stored information from a storage carrier with a low light emission horn. An object of the present invention is to provide a semiconductor light emitting device.

<Means for Solving the Problems> In order to achieve the above object, a semiconductor light emitting device of the present invention includes a plurality of laser chips disposed at different positions and having different reflectances of laser emission surfaces, and a plurality of laser chips described above. It is characterized by having a hologram diffraction grating that directs laser beams incident from different sources along different optical paths to the target object and outputs them along the same optical path.

Effect> When writing to a record carrier, a laser beam is emitted toward the hologram diffraction grating from a laser chip whose laser emission surface has a lower reflectance among a plurality of laser chips arranged at different positions. The hologram diffraction grating diffracts or transmits this laser light as it is, and emits it toward the object along a predetermined optical path. Therefore, as in the past, the light emission output is increased by using the laser chip with low reflectance.
It becomes possible to write with a strong laser beam.

On the other hand, when reading stored information from a record carrier, a laser beam is emitted toward the hologram diffraction grating from a laser chip whose laser emitting surface has a higher reflectance among the plurality of laser depths arranged at different positions. . The above-mentioned diffraction grating diffracts this laser light or transmits it as it is,
The light is emitted toward the target object along the same optical path as the optical path during writing. At this time, since a laser chip with a higher reflectance is used, the return light that is reflected by the object and reaches this laser chip hardly enters into the inside of the laser chip. Therefore, even if the light emission output of the laser chip is low, reading can be performed with a high S/N ratio.

<Examples> Hereinafter, the semiconductor light emitting device of the present invention will be explained in detail with reference to Examples.

FIG. 1 shows a semiconductor light emitting device according to an embodiment of the present invention! This shows an example in which an optical pickup is configured using 0. In addition to the semiconductor light emitting device IO, this optical pickup includes a beam splitter 14, a collimating lens 15, and an objective lens I6, similar to the conventional optical pickup shown in FIG.
and a light receiving element I8. The above semiconductor light emitting device 1
0 consists of a writing semiconductor laser chip 11 and a reading laser chip 12 arranged at different positions, and a hologram diffraction grating 13. The writing semiconductor laser chip 11 has the same structure as the semiconductor laser chip 2I shown in FIG. That is, an AR coating 31 is applied to the front surface 20 of the chip to lower the reflectance, while a high reflection coat 32 is applied to the rear surface 30 of the chip to increase the reflectance. In this way, the light emission output is increased. As shown in FIG. 4, the reading laser chip 21 has a half-wavelength (λ/2) coating 41.
41 to make the reflectance on the front surface 40 side higher than the reflectance on the front surface 20 side of the semiconductor laser chip 11 for writing. Hologram diffraction grating 3 includes a hologram 13a formed by an interference pattern of laser beams from a semiconductor laser chip 11 for writing and a semiconductor laser chip 12 for reading. Then, the zero-order light that is emitted from the writing semiconductor laser dip 11 and passes through the hologram 13a as it is, and the first-order light that is the emitted light from the readout semiconductor laser that is diffracted by the hologram 13a pass through the same optical path. There is.

First, the operation of writing to the record carrier 17 (shown in FIG. 1) will be explained. Laser light emitted by the writing semiconductor laser chip 11 at high output is incident on the hologram diffraction grating 13 . The zero-order light that has passed through the hologram 13a passes through the beam splitter 14, the collimating lens 15, and the objective lens 16 in order, and then enters the record carrier 17, where data is written in the same manner as in the prior art.

The laser beam is reflected by the record carrier I7, and the reflected light is reflected again by the objective lens 16. After passing through the collimating lens 15, the beam is split by the beam splitter [4] and then sent to the light receiving element 1.
8. A servo signal is obtained from the output signal of the light receiving element I8 by a processing circuit (not shown).

Next, the reading operation will be explained. The laser light emitted at low output from the reading semiconductor laser chip 12 enters the hologram diffraction grating 13 through a different optical path from the laser light emitted from the writing semiconductor laser chip 11. The first-order light diffracted by the hologram 13a is emitted along the same optical path as the zero-order light during writing. And beam splitter 14, collimating lens 15. The light passes sequentially through the objective lens (6) and enters the record carrier 17. Record carrier 17
The reflected light is modulated by the recorded information and reflected, and after passing through the objective lens 16 and collimating lens I5 again, it is split by the beam splitter 14 and enters the light receiving element 18. Then, a reproduction signal and a servo signal are obtained from the output signal of the light receiving element 18 by a processing circuit (not shown).

When operating in this way, the writing laser chip 11
Since the reflectance of the laser emitting surface 40 of the reading laser chip 12 is higher than the reflectance of the laser emitting surface 20 of the laser chip 12, the return light that is reflected by the record carrier 17 and reaches this laser chip 12 is It won't penetrate much inside. Hence the readout laser chip! Even if the light emission output of No. 2 is low, reading can be performed with a high S/N ratio.

<Effects of the Invention> As is clear from the above, the semiconductor light emitting device of the present invention includes a plurality of laser chips that are arranged at different positions and have different reflectances on the laser emission surfaces, and a plurality of laser chips that are incident on different optical paths from the plurality of laser chips. Since it is equipped with a hologram diffraction grating that directs the laser beam to the target and emits it on the same optical path, a laser chip with a low reflectance on the laser emission surface can be used for writing that requires high light output, while the laser emission To reduce the influence of returned light and increase the S/N ratio when reading stored information from a storage carrier by operating a laser chip with a high surface reflectance at low light emission output and using it for reading. I can do it.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical pickup configured with a semiconductor light emitting device according to an embodiment of the present invention, FIG. 2 is a diagram showing a conventional optical pickup, and FIG. 3 is a diagram showing a semiconductor laser chip of the conventional optical pickup. FIG. 4 is a diagram showing the structure of a readout semiconductor laser chip of the semiconductor light emitting device. 0... Semiconductor light emitting device, 1... Semiconductor laser chip for writing, 2... Semiconductor laser chip for reading, 3... Hologram diffraction grating, 3a... Hologram, 4.22... Beam splitter, 5.23... Collimating lens, 6.24... Objective lens, 17.25... Record carrier, 8.26... Light receiving element, 0.40... Laser emission surface, 30.50... ··back face,
3 1... AR co-coating, 2... High reflection coating, I... λ/2 coating.

Claims (1)

[Claims] (1) Hologram diffraction in which multiple laser chips are arranged at different positions and have different reflectances on their laser emission surfaces, and the laser beams incident from the multiple laser chips on different optical paths are directed toward the target and emitted along the same optical path. A semiconductor light emitting device characterized by being equipped with a lattice.