Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-04-26
2003-04-01
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S046012
Reexamination Certificate
active
06542526
ABSTRACT:
TECHNICAL FIELD
The present invention relates to optical information processing equipment such as an optical disk apparatus and a light source, particularly, a semiconductor light emitting device suitable therefor.
BACKGROUND ART
With regard to optical information processing equipment represented by a DVD (Digital Video Disk) apparatus, there have been strong demands to increase the capacity thereof. In particular, it has been required to provide optical information processing equipment capable of processing images of high-definition TVs. As such information processing equipment, there has been generally known a type adopting a photomagnetic recording or phase transition recording method. However, there has yet to be realized an optical recording equipment capable of sufficiently processing dynamic images of high-definition TVs.
On the other hand, with regard to a semiconductor light emitting device used as a light source of such optical information equipment, it has been required to shorten the wavelength toward a wavelength range from that of blue light to that of near ultraviolet light. The reason for this is that a blue color based semiconductor light emitting device is useful for high density recording or reproducing of information in or from a recording medium because such a light emitting device is capable of emitting light having a shorter-wavelength thereby focussing the light at a smaller light spot.
Based on such a background, development has been actively made of a blue color semiconductor light emitting device using a gallium nitride based compound semiconductor such as GaN, GaAlN, InGaN or InGaAlN allowing emission of light having a wavelength in a wavelength range from that of blue light to that of ultraviolet light.
At present, as a light emitting device using the above-described material, a high-intensity blue color LED having a double-hetero structure using a Zn-doped InGaN layer provided on a sapphire substrate as a light emitting layer has been put in practical use (S. Nakamura et al., Appl. Phys. Lett., 64 (1994) 1687). In recent years, continuous oscillation at room temperature of a semiconductor laser device using an undoped InGaN quantum well layer provided on a sapphire substrate as a light emitting layer has been realized (S. Nakamura et al., Appl. Phys. Lett. 69 (1996) 4056). This semiconductor laser device, however, has required a high operational current density, thereby failing to obtain sufficient characteristics from the viewpoint of practical use. Also, in recent years, pulsive oscillation at room temperature of a semiconductor laser using an undoped InGaN quantum-well layer provided on a sapphire substrate as a light emitting layer has been realized (S. Nakamura et al., Jpn. J. Appl. Phys. 35 (1996) L74). This semiconductor laser device, however, has also required a high operational current density, thereby failing to realize continuous oscillation thereof.
In the meantime, a semiconductor laser device including an active layer of a modulation doping structure, thereby allowing operation at a low threshold value has been disclosed in Japanese Patent Laid-open No. Sho 62-249496.
A semiconductor light emitting device of a type using a gallium nitride based material has been also reported, for example, in Jap. J. Appl. Phys. Vol. 35 (1996) Pt. 2, No. 1B, pp. L74-L76, or Japanese Patent Laid open No. Hei 8-64912. The former document has disclosed a semiconductor laser device having an InGaN based multi-quantum well structure, and the latter document has disclosed a semiconductor light emitting device using a gallium nitride based material. In the methods disclosed in both the documents, the semiconductor light emitting device is configured by forming a wurtzite type gallium nitride based semiconductor layer on a sapphire substrate. In addition, the active layer in the latter device has no quantum-well structure.
DISCLOSURE OF INVENTION
1. Information Processing Equipment
A first object of the present invention is to provide information processing equipment capable of sufficiently recording or reproducing even dynamic images in or from high-definition TVs or the like. The optical information processing equipment is typically configured as an optical disk apparatus adopting, for example, photomagnetic recording or phase transition recording method.
A second object of the present invention is to provide optical information processing equipment capable of ensuring recording or reproducing of high-definition dynamic images under various environments, particularly, under a high temperature environment.
A third object of the present invention is to provide optical information processing equipment enabling high density recording and prolonging the service life.
It should be noted that the optical information processing equipment of the present invention allows not only writing operation of information but also reading operation of information.
Principal aspects of the present invention disclosed in this Description will be described below in connection with the above-described objects.
(1) According to a first aspect of the present invention, there is provided optical information processing equipment including at least a light source for irradiating a recording medium with light and an optical system for focussing light on the recording medium, and having a function of performing recording by changing a state of part of the recording medium, characterized in that a wavelength of light emitted from the light source is in a wavelength range of 350 nm to 550 nm, a threshold current density of the light source is in a range of 2.2 kA/cm
2
or less, and a recording density of the recording medium is in a range of 15 GB or more. To achieve the above object, the threshold current density of the light source is preferably in a range of 1.0 kA/cm
2
or less, more preferably, in a range of 0.8 kA/cm
2
or less.
The light source exhibiting a threshold current density in the above range is capable of sufficiently realizing optical output of 40 mW or more at a drive current of 100 mA, for example, at an atmospheric temperature of 70° C.
The optical information processing equipment of the present invention is significantly desirably usable while satisfying requirements of recording media such as high-definition TVs. In a high-definition TV, an information transfer speed for transferring a dynamic image is in the order of, for example, 10 MB/sec. The known recording equipment has failed to record such a large capacity of information. On the contrary, according to the inventive equipment, since the recording density of a recording medium is in the range of 15 GB or more, the equipment enables recording of a dynamic image in a high-definition TV. Also, according to the inventive equipment, since the light source allows emission of light in the wavelength range of 350 nm to 550 nm, that is, emission of visible light, particularly, blue light, violet light or ultraviolet light, the above-described recording density can be realized on one surface of the disk. Further, according to the inventive equipment, the threshold current density of the light source is low and, therefore, it is possible to require less power and, hence, to reduce the power consumption. The threshold current density of the light source of the inventive equipment is substantially reduced to half as compared with the general threshold current density of the conventional blue color or violet color based semiconductor laser device. Accordingly, the light source of the inventive equipment is able to reduce the drive power and hence to meet the practical requirements of the present product market.
To achieve the above objects, the wavelength of light emitted from the light source is preferably in a range of 350 nm to 430 nm. This is advantageous in simplifying the optical system.
(2) According to a second aspect of the present invention, there is provided optical information processing equipment including at least a light source for irradiating a recording medium with light and an optical system for focussing
Kuroda Takao
Niwa Atsuko
Ohtoshi Tsukuru
Okai Makoto
Shimano Takeshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Leung Quyen
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