Coherent light generators – Particular resonant cavity – Specified cavity component
Reexamination Certificate
1998-12-17
2001-06-26
Font, Frank G. (Department: 2877)
Coherent light generators
Particular resonant cavity
Specified cavity component
C372S014000, C372S016000, C372S020000
Reexamination Certificate
active
06252897
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an external mirror type wavelength tunable laser, and particularly to an external mirror type wavelength tunable laser which can tune the wavelength so as to be used suitably for optical communication.
BACKGROUND OF THE INVENTION
In recent years, improvements in performance of computer are remarkable so that computer-computer communications are implemented usually in ordinary home. Furthermore, internet is developed in world-wide scale so that circumstances in communication are changed violently.
Under these circumstances, information is required instantly by one who is concerned with communications. Upon demand at such request, optical-fiber telecommunication system by which a large amount of various information can be transmitted at high-speed is utilized as the media.
Recently, it is required to transmit at real time not only character information, but also a variety of information such as still image, dynamic image and speech data, so that high-capacity optical-fiber telecommunication system becomes developed.
Moreover, in order to transmit data through an optical-fiber telecommunication system over great distances, it is required to amplify lightwave signals in the course of optical-fiber line. In this respect, introduction of erbium doped optical-fiber amplification (EDFA) is made also as means for light amplification.
When EDFA system is applied as means for light amplification, wavelength division multiplex is performed within a wavelength band of EDFA (about 30 nm in the existing state) to make mass-storage of data, so that the above described transmission system is proceeding toward practical utilization.
In this system, a number of light sources each having a specified wavelength are required. In the case where a plurality of light sources are used, there are disadvantages of high cost, upsizing of equipment, high consumption of energy and the like, and hence, it is desired to eliminate these disadvantages.
Accordingly, it is desired to realize a wavelength tunable laser in which a wavelength can be tuned arbitrarily within the wavelength band of EDFA, i.e., that of about 30 nm, so that the wavelength can be specified to a predetermined wavelength.
Wavelength tunable lasers are classified broadly into semiconductor monolithic types and external mirror types. As to the semiconductor monolithic type wavelength tunable laser, no practical unit exists which can tune wavelength within a range of wavelength as wide as about 30 nm corresponding to that of EDFA.
On the other hand, the disadvantage of the external mirror type is that a mechanism for rotating a grating type reflector becomes upsizing. Where such grating type reflector is used as the external mirror so that tuning is done by changing the incident angle of light, wherein a manner for rotating the grating reflector by the use of a motor and the like manner is required.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an external mirror type wavelength tunable laser having a simple structure and capable of tuning an emitting wavelength.
According to the invention, an external mirror type wavelength tunable laser, comprises a semiconductor laser having one end plane of a reduced reflection factor; a lens provided to face the one end plane of the semiconductor laser; a grating type reflector for reflecting a light supplied via the lens from the one end plane of the semiconductor; and means for shifting the lens in a direction orthogonal to a light axis of the lens to change an incident angle of the light to the grating type reflector.
It is preferred that the above described shifting means is a piezoelectric element.
Furthermore, it is preferred that focal point of the lens is set on the above described end plane of the semiconductor laser.
Moreover, it is preferred that the light outputted from the above described end plane is converted into parallel light.
Further, it is preferred that the above described lens is an aspherical lens.
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Patent Abstracts of Japan; Vublication No. JP 01 286488 A (Matsushita Electric Ind. Co. Ltd.); vol. 14, No. 67 (E-0885); dated Feb. 7, 1990.
Patent Abstracts of Japan; Publication No. JP 57 085281 A (Tomijima Takumi); vol. 6, No. 170 (E-128); dated Sep. 3, 1982.
Font Frank G.
McGinn & Gibb PLLC
NEC Corporation
Rodriguez Armando
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