Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-04-16
2001-02-06
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
Reexamination Certificate
active
06185237
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor laser used as a light source of an optical disk system, or the like.
BACKGROUND ART
In recent years, the demand for semiconductor lasers has been increasing in the field of optical communication, laser printers, optical disks, and the like, and research and development therefor have been actively conducted mainly for those of the GaAs type and the InP type. In particular, in the field of optical information processing, a system for recording/reproducing information using particularly AlGaAs type semiconductor laser light having a wavelength of about 780 nm has been put to practical use, and has been widely used in a compact disk, and the like. Recently, however, a further increase in a storage capacity has been more in demand for these optical disk devices, and the need for implementation of a laser having a short wavelength has been increasing correspondingly.
In this respect, an AlGaInP type semiconductor laser can oscillate in a red range between about 620 nm and about 690 nm, producing light having the shortest wavelength among the semiconductor lasers which are at the current level of practical use, Accordingly, the AlGaInP type semiconductor laser is promising as a next-generation light source for large capacity optical information recording in place of the conventional AlGaAs type semiconductor laser.
A conventional semiconductor laser is disclosed by D. P. Bour et al. in the Journal of Quantum Electronics, vol. 30, No. 2, pp. 593-606 (February 1994). The semiconductor laser disclosed in this article includes an active layer having a multiple quantum well structure formed on a substrate, achieving an output of 5 mW at an oscillation wavelength of 680 nm.
However, as the oscillation wavelength is shortened, a bandgap in the active layer is increased, and an offset &Dgr;Eg of a bandgap between the active layer and a cladding layer is reduced correspondingly. Therefore, a carrier overflow due to current injection occurs, resulting in an increased threshold current and thus an increased operating current. Such a phenomenon is not preferable for implementing a higher output of the semiconductor laser.
DISCLOSURE OF THE INVENTION
A semiconductor laser of the present invention includes an active layer, and a buried layer for absorbing laser light emitted from the active layer, wherein an oscillation wavelength of the laser light is in a 650 nm band, an oscillation mode is a single transverse mode, and a peak of a light intensity distribution of the laser light is placed on a side opposite to the buried layer with respect to a center of the active layer.
In one embodiment, the semiconductor laser further includes a pair of optical guiding layers formed on both sides of said active layer, and the pair of optical guiding layers have an asymmetric structure. For example, a thickness of a first layer of said pair of optical guiding layers which is located on a side opposite to said buried layer with respect to said active layer is larger than a thickness of a second layer which is located on a side of the buried layer with respect to the active layer. Preferably, in said pair of optical guiding layers, a ratio of the thickness of said first layer to the thickness of said second layer is in a range from about 2 to about 8.
In one embodiment, a total thickness of said pair of optical guiding layers is between about 0.03 &mgr;m and about 0.12 &mgr;m.
Preferably, the peak of the light intensity distribution of said laser light is shifted by about 5 nm to about 10 nm from the center of said active layer.
The peak of the light intensity distribution of said laser light may be placed inside said active layer.
Said active layer may have a multiple quantum well structure.
Said active layer may be formed on an off substrate.
In one embodiment, a layer having a smaller refractive index than a layer adjacent thereto is provided at a position on a side opposite to said buried layer with respect to said active layer.
The oscillation wavelength may be in a 630 nm band instead of in the above-mentioned 650 nm band.
According to another aspect of the present invention, an optical disk device including a semiconductor laser having such features as described above, an optical system for collecting laser light emitted from the semiconductor laser onto a recording medium, and an optical detector for receiving reflected light from the recording medium is provided.
In the optical disk device, information may be recorded onto said recording medium using said semiconductor laser as a light source.
Said optical detector may be located in a vicinity of said semiconductor laser.
In one embodiment, said optical detector is formed on a silicon substrate, and said semiconductor laser is provided on the silicon substrate. For example, said semiconductor laser is provided in a recess formed in said silicon substrate, and laser light emitted from the semiconductor laser is reflected by a micromirror formed at the silicon substrate to travel in a direction substantially perpendicular to a surface of the silicon substrate. A metal layer may be formed on a surface of said micromirror.
Thus, the present invention has an objective of providing a semiconductor laser having operating characteristics suitable for achieving a higher output, wherein a small threshold current value is retained even when the oscillation wavelength is shortened.
REFERENCES:
patent: 4982409 (1991-01-01), Kinoshita et al.
patent: 5065404 (1991-11-01), Okajima et al.
patent: 5355384 (1994-10-01), Inoue et al.
patent: 5406574 (1995-04-01), Rennie et al.
patent: 64-27286 (1989-01-01), None
patent: 64-46243 (1989-02-01), None
patent: 1-150244 (1989-06-01), None
patent: 2-74088 (1990-03-01), None
patent: 3-44085 (1991-02-01), None
patent: 4-61635 (1992-02-01), None
patent: 5-243669 (1993-09-01), None
patent: 6-112586 (1994-04-01), None
patent: 6-181360 (1994-06-01), None
patent: 7-99366 (1995-04-01), None
“LDH (Laser-Detector-Hologram) Unit for Extremely Thin Optical Pick-up”,Journal of the Society of Circuit Mounting,vol. 10 No. 5, pp. 336-340 ( with partial translation), no month or year.
D.P. Bour et al., “Strained Ga&khgr;In1-&khgr;P/(A1Ga)0.5In0.5P Heterostructures and Quantum-Well Laser Diodes”,IEEE Journal of Quantum Electronics,vol. 30 No. 2, pp. 593-606 (Feb. 1994).
E. Yablonovitch et al. “Reduction of Lasing Threshold Current Density by the Lowering of Valence Band Effective Mass”,Journal of Lightwave Technology,vol. LT-4, No. 5, pp. 504-506 (May 1986).
International Search Report corresponding to application No. PCT/JP97/02171 dated Oct. 7, 1997.
Adachi Hideto
Fukuhisa Toshiya
Kidoguchi Isao
Mannoh Masaya
Takamori Akira
Davie James W.
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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