JPS62150788A - Optical information processor - Google Patents

Abstract

PURPOSE:To permit the densification by providing a semiconductor laser which generates a high-output short pulse train as the peak power and a secondary high-frequency generator which uses a beam of light emitted from this semiconductor laser as the primary light beam. CONSTITUTION:A laser beam 6 emitted from one end surface (resonance interface) 4 of a semiconductor laser 2 is photo-feed back to the semiconductor laser 2 by an external reflector 8. At this time, when a semiconductor laser (modulator) 10 is current- modulated in a frequency equivalent to the roundtrip frequency during the time the beam 6 emitted from the laser comes returning, a laser beam 12 generates a pulse train which has a very large peak power and is secularly short. When the laser beam 12 having this large peak power is incident on a nonlinear optical crystal 14, which is used as the secondary high-frequency generator, as a primary beam of light, a secondary beam 16 obtained is very large as peak power and the secondary beam 16 passes through an optical system 18 composed of a lens and so on and is led to an optical system 18 composed of a lens and so on and is led to an optical disc 20. That is, this device has a high-output short pulse train generating semiconductor laser 22, which generates a high-output short pulse train as the peak power, and a secondary high-frequency generator 24.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information texturing device using a high-output short wavelength light source.

Conventional technology Semiconductor lasers are small, consume little power, and have excellent reliability, and are currently widely used in optical information processing devices such as optical disks and printers. Because it can be recorded, it is widely studied. In order to increase the density of optical disks, it is necessary to shorten the oscillation wavelength of the semiconductor laser and reduce the beam spot size. Therefore, in addition to the AdGaAs/GaAs system, which is currently being mass-produced, GaAs is a new material. The A77GalnP system on a substrate or the InGaAsP system on a G&MsP substrate has become the subject of research. However, even with this new semiconductor material, the wavelength that can be oscillated is approximately 0.6 μm.
However, it is not possible to achieve anything smaller than that, and therefore, in order to further reduce the beam spot size and achieve higher density, a semiconductor laser with a shorter wavelength is required.

On the other hand, it is known that wavelength conversion is theoretically possible by second harmonic generation (SHG) when a crystal with a larger nonlinear optical constant than the conventional one is used.

SHG materials include, for example, inorganic materials such as LiNbO3 and organic materials such as MNA.

As shown in FIG. 3, laser light 62 with wavelength λ0 emitted from semiconductor laser 6o is converted by SHG material 54 into secondary light 66 with wavelength λo/2.

Therefore, the wavelength can be easily shortened.

Problems to be Solved by the Invention However, in the past, the power of this wavelength-converted secondary light was extremely small. For example, an SH made of LiNbO5 in which a semiconductor laser beam with an output of 60 mW is made into an optical waveguide.
Even if it enters the G material 54, the power of the secondary light is at most 5
It was about μW, and could not be used for optical information processing devices such as optical disks. SHG uses nonlinear optical effects, so increasing the incident primary optical power can increase the secondary optical power, but when using a semiconductor laser in CW, the limit is about 100 mW at most from the viewpoint of reliability etc. Therefore, it was impossible to obtain sufficient secondary optical power, and it was not possible to provide it to an optical information processing device.

In view of these problems, the present invention has developed a semiconductor laser that can be used as a single semiconductor laser.
The purpose is to sufficiently increase the power of the second order light of the second harmonic, so that it can be applied to optical information processing equipment as a short wavelength light source. As a means to solve these problems, the present invention provides a semiconductor laser device that generates a high output short pulse train as a peak power, and a second harmonic laser device that uses the light emitted from the semiconductor laser device as the primary light. It has a wave generating device, and uses, for example, a mode-locked semiconductor laser device or a Q-switch semiconductor laser device as the semiconductor laser device.

Effect If the above means is used, the output light from the second harmonic generator will have a much larger output power than the conventional one, and therefore an optical information processing device using this light source will be able to achieve higher density. It has an effect.

EXAMPLES The present invention will be explained below using examples. FIG. 1 shows an embodiment of the present invention. A laser beam 6 emitted from one end surface 4 of the semiconductor laser 2 is optically returned to the semiconductor laser 2 by an external reflector 8. At this time, when the semiconductor laser 10 is current-modulated at a frequency corresponding to the round-trip frequency until the light 6 emitted from the laser returns, the laser light 12 generates a pulse train with a very high peak power and a short time. A nonlinear optical crystal 14 which is a second harmonic generator uses this laser beam 12 having a large peak power as primary light.
The secondary light 16 obtained when incident on the optical disk 16 has a very large peak power, and passes through an optical system 18 composed of lenses and the like, and is guided to the optical disk 20. That is, in the optical information processing apparatus according to one embodiment of the present invention, 22 is a semiconductor laser device that generates a high-output short pulse train as a peak power, and 24 is a second harmonic generator.

FIG. 2 shows a comparison of the output powers of the conventional example and this embodiment.

A semiconductor laser beam with an output power of usually about 50 mW as shown in Fig. 2 (a-1) is
When it enters the harmonic generator, the output of the secondary light is the second harmonic.
As shown in Figure (2L-2), it is about 5μW at most, but the first
If mode-locking is applied to a semiconductor laser as in the embodiment shown in the figure, a peak power of about 1 W or more can be obtained relatively easily as shown in Fig. 2 (b-1). As shown in FIG. 2 (b-2), the secondary light converted to half the wavelength by the secondary harmonic generator can sufficiently obtain a peak power of about 60 mW or even more. Therefore, the optical information processing device according to the present invention can be used as a light source with half the wavelength of a normal semiconductor laser and with extremely high output power.

Comparing FIG. 2 (IL-2) and FIG. 2 (b-2), the secondary light output of the optical information processing device of this embodiment is not CW light but a temporally short pulse train. The time interval t of this pulse train can be expressed as L, where L is the distance from the semiconductor laser 2 to the external reflector 8 in FIG. 1, and C is the speed of light. That is, the modulation frequency f of the semiconductor laser for mode-locking is J'=-L. Therefore, if L=15cm, f=IGH2゜t
= 1 n5ec.

In an actual optical information processing device, for example, an optical disk, the modulation band for writing is about 1 oMHz at most. In other words, the interval between signal pits is 100n86C in terms of time.
However, if a mode-locked semiconductor laser such as that of the present invention is used, the signal is mode-locked at a sufficiently high frequency, so the envelope can be regarded as DC, and there is no problem at all. Note that L may be even shorter.

As described above, the optical information processing device of the present invention has a very large power at half the wavelength of a normal semiconductor laser, and can be used as CW light in appearance, so it can significantly increase the density of optical disks, etc. can be achieved.

Although the embodiment shown in FIG. 1 shows the case of active mode locking as a mode-locking semiconductor device, FIG. The present invention is not limited to this embodiment. Furthermore, by inserting an external modulator, it is possible to use it not only as DC light but also for writing. Alternatively, it may be used for writing by Q-switch operation without using an external modulator. In addition, the single semiconductor laser to be used is A4
It may be made of any material other than GaAs. In addition, the nonlinear optical crystal used as the second harmonic generator may be made of an inorganic material such as LiNbO5 or an organic material such as MN.In order to increase efficiency, it is preferable to form it into an optical waveguide. desirable.

Effects of the Invention As described above, the optical information processing device of the present invention has half the wavelength compared to devices using conventional semiconductor lasers, so the beam spot size can be reduced, extremely high density can be achieved, and high output power can be achieved. By performing this operation, it is possible to have not only playback but also recording and erasing functions, which has a great effect.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an optical information processing device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the difference in output power characteristics between this embodiment and a conventional example, and Fig. 3 is a diagram of a conventional optical information processing device. FIG. 2 is a schematic configuration diagram for explaining second harmonic generation of the device. 2...Semiconductor laser, 4...Cavity surface, 6...Laser light, 8...External reflector, 1o...Modulation instrument, 12... laser beam, 14... nonlinear optical crystal, 16...
Secondary light, 18... Optical system, 2o... Optical disk, 22... High output short pulse train generation semiconductor laser device, 24... Second harmonic wave generator.

Claims (3)

[Claims] (1) An optical information processing device comprising a semiconductor laser device that generates a high-output short pulse train as peak power, and a second harmonic generator that uses the light emitted from the semiconductor laser device as primary light. (2) The optical information processing device according to claim 1, which uses a mode-locked semiconductor laser device as the semiconductor laser device. (3) The optical information processing device according to claim 1, which uses a Q-switch semiconductor laser device as the semiconductor laser device.