Coherent light generators – Particular resonant cavity – Distributed feedback
Reexamination Certificate
1999-01-27
2001-10-09
Davie, James W. (Department: 2881)
Coherent light generators
Particular resonant cavity
Distributed feedback
C372S046012
Reexamination Certificate
active
06301283
ABSTRACT:
This application claims the benefit of Japanese Patent Application No. 10-30546, filed Jan. 28, 1998, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser, and more particularly, to a distributed feedback semiconductor laser (hereinafter referred to as a DFB semiconductor laser) having a wavelength varying function.
2. Discussion of the Related Art
The DFB semiconductor laser is known as a device that has various applications in optical communication systems such as in optical cable television (CATV) technology, pumping light sources of an SHG short-wavelength laser for high-density information recording and of a small size solid-state laser, optical measurements, and the like. The conventional DFB semiconductor laser is commonly manufactured by a 2-stage (or more) epitaxial growth. Such DFB lasers are manufactured by forming a diffraction grating on a waveguide layer and then growing other layers epitaxially on the waveguide.
To avoid the complexity involved with an epitaxial growth of two or more stages, DFB semiconductor lasers have been developed that are manufactured having a 1-stage epitaxial growth. In recent years, the importance of providing such DFB semiconductor lasers with variable oscillation wavelengths has continued to increase.
Accordingly, DFB semiconductor lasers having variable oscillation wavelengths incorporating a chirped diffraction grating structure have been proposed. The chirped diffraction grating structure is classified into, for example, (a) a structure in which the diffraction grating of a DFB semiconductor laser is given a non-uniform pitch, and (b) a structure in which the diffraction grating of a DFB semiconductor laser is given a constant pitch and a bent waveguide is formed on a waveguide layer. The oscillation wavelength is varied in those manners.
However, method (a) requires a complex and difficult laser manufacturing process and hence it is not suitable for mass-production because a non-uniform diffraction grating needs to be formed. Method (b) results in a large loss of light because the light traveling direction is not perpendicular to the diffraction grating.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a distributed feedback (“DFB”) semiconductor laser and manufacturing method that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An objective of the present invention is to provide a DFB semiconductor laser that is capable of varying its oscillation wavelength, has a simple structure, is easy to manufacture and suitable for mass production, and results in a small loss of light.
Additional features and advantages of the present invention will be set forth in the description which follows, and will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure and process particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a distributed feedback semiconductor laser of the present invention includes a semiconductor substrate having a bottom surface and a top surface; an active layer formed on the top surface of the semiconductor substrate; a ridge stripe formed on the active layer and having a first surface and extending in a first direction; a periodic structure that is periodic in the first direction; a plurality of p-type electrodes formed on the first surface of the ridge stripe; and an n-type electrode formed on the bottom surface of the semiconductor substrate, wherein the first surface of the ridge stripe is parallel with a growth plane of the active layer, the first surface having at least two different widths in a direction perpendicular to the first direction.
In another aspect, the present invention provides a distributed feedback semiconductor laser that includes a semiconductor substrate; a first cladding layer formed on the semiconductor substrate; a first guide layer formed on the first cladding layer; an active layer formed on the first guide layer; a second guide layer formed on the active layer; a second cladding layer formed on the second guide layer; a contact layer formed on the second cladding layer; a ridge stripe, including the second cladding layer and the contact layer, extending in a light emitting direction; a diffraction grating formed on the second cladding layer; a plurality of p-type electrodes formed on the ridge stripe; and an n-type electrode formed on a bottom surface of the semiconductor substrate, wherein the ridge stripe has at least two different widths in a direction perpendicular to a ridge stripe extending direction.
In a further aspect of the present invention, a method of manufacturing a distributed feedback semiconductor laser includes the steps of forming a first cladding layer on a semiconductor substrate; forming a first guide layer on the first cladding layer; forming an active layer on the first guide layer; forming a second guide layer on the active layer; forming a second cladding layer on the second guide layer; forming a contact layer on the second cladding layer; providing a ridge stripe, including the second cladding layer and the contact layer, extending in a light emitting direction; forming a diffraction grating on the second cladding layer; forming a plurality of p-type electrodes on the ridge stripe; and forming an n-type electrode on a bottom surface of the semiconductor substrate, wherein the step of providing a ridge stripe includes the step of providing the ridge stripe with at least two different widths in a direction perpendicular to a ridge stripe extending direction.
It is to be understood that both the foregoing general description and the following detailed description arc exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
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N. Chen, et al. “Analysis, Fabrication, and Characterization of Tunable DFB Lasers with Chirped Gratings,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 3, No. 2, pp. 541-546, Apr. 1997.
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Chen Nong
Chikuma Kiyofumi
Takei Kiyoshi
Watanabe Yoshiaki
Davie James W.
Morgan & Lewis & Bockius, LLP
Pioneer Electronic Corporation
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