Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
2001-01-10
2004-09-28
Wong, Don (Department: 2828)
Coherent light generators
Particular beam control device
Optical output stabilization
C372S043010, C372S044010, C372S045013, C438S031000
Reexamination Certificate
active
06798798
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor laser apparatus, and a semiconductor laser module, having a structure in which structures for implementing a desirable optical output power and a high energy conversion efficiency from input electric power to output optical power are adequately combined.
BACKGROUND OF THE INVENTION
Recently, with widespread use of various communication media such as the Internet, there have been increased demands for optical communication to be greater in capacity. In the optical communication in the past, at respective bands of wavelengths 1310 nm and 1550 nm where the absorption of light by an optical fiber is small, the transmission generally was performed by a single wavelength. In this system, for a greater quantity of information to be transmitted, it was necessary to install a greater number of cores of optical fibers in the transmission path, with increase in cost following increase in transmission capacity, as a problem.
For this reason, there has been applied a WDM (wavelength division multiplexing) communication system. The WDM communication system mainly employs an EDFA (Erbium Doped Fiber Amplifier), which is for a system that has a 1530-1570 nm band as an operation band, where it uses a plurality of wavelengths to perform transmission. This DWDM communication system or WDM communication system uses a single optical fiber for concurrent transmission of a plurality of optical signals different in wavelength, allowing for the network to have a greatly increased transmission capacity, without needing the installation of additional optical fiber lines (i.e., “new lines”).
For excitation of the EDFA, there have been employed high-output pumping semiconductor laser modules. Among them, the 1480 nm-band pumping semiconductor laser module has advantages, such as 1) high reliability, 2) high conversion efficiency of erbium doped fiber, with merit in adaptation for the amplifier to be high of output, 3) wide absorption band of erbium doped fiber, enabling synthesis at multiple wavelengths, and 4) availability of peripheral optics such as isolators, wavelength synthesizers, and polarization synthesizers. As a result, by the use of wavelength synthesis, polarization synthesis, and the like, and by use of a plurality of pumping semiconductor laser modules, there has been implemented an pumping light source for high-output optical fiber amplifiers, and adapted for use in an optical fiber amplification system.
In general, in the semiconductor laser device (as a semiconductor laser apparatus), when injected electric current is increased, the optical output power increases. However, due to heat dissipation of the semiconductor laser device itself, a saturation in output power appears at a certain driving current, and thereafter the optical output power will not increase even with an increased driving current.
For the saturating driving current to be increased in value, the semiconductor laser apparatus had a cavity length elongated so that a desirable optical output power was obtained. On the contrary, to reduce the driving current required to obtain a desirable optical output power, there was selected an adequate cavity length, so that a semiconductor laser apparatus was configured with the selected cavity length.
FIG. 14
is a graph showing a driving current vs. optical output power relationship for the cavity length of semiconductor laser apparatus taken as a parameter. For example, in case of a semiconductor laser apparatus to be adapted for an optical output power of 360 mW, a cavity length of 1200 &mgr;m was adopted so that the driving current was minimized in FIG.
14
.
However, elongation of the cavity length in semiconductor laser apparatus accompanied variation in physical configuration of the semiconductor laser apparatus, with a result that, in case of determination of the cavity length of semiconductor laser apparatus simply depending on driving current, the electric drive power involved increases, not simply in electric power consumed for optical output power of the semiconductor laser apparatus, but also of reactive power consumed at other parts in the semiconductor laser apparatus itself, such as due to serial resistance and thermal resistance, sometimes causing, as a problem, a reduction of the photoelectric power conversion efficiency. (The photoelectric power conversion efficiency is often defined as an optical output power of a semiconductor laser apparatus divided by electric drive power of the semiconductor laser apparatus.)
Moreover, with increase in reactive power consumed by semiconductor laser apparatus, that is, in the difference between electric drive power and optical output power, which is mainly converted to heat, there was the need for a heat dissipating structure to be large, resulting in a large-sized semiconductor laser module for incorporation of the semiconductor laser apparatus, as a problem. The prior art has not investigated or considered selecting the value of the cavity length to minimize the electric drive power or to maximize the photoelectric conversion efficiency for a given optical output power. In addition, the prior art has not investigated or considered selecting the value of other laser parameters, such as an impurity carrier concentration in an upper cladding layer of the laser, to minimize input drive power or to maximize conversion efficiency.
SUMMARY OF THE INVENTION
The present invention has been made with such points in view. It therefore is an object of the present invention to provide, in implementation of a semiconductor laser apparatus adapted for a desirable optical output power, a semiconductor laser apparatus having its electric drive power rendered minimal or its photoelectric conversion efficiency rendered maximal, as well as a fabrication method of the same, and a semiconductor laser module with the same. (The photoelectric conversion efficiency is the energy conversion efficiency of electrical power to optical power.)
To achieve the object, according to a first aspect of the invention, there is provided a semiconductor laser apparatus wherein a respective element value of the semiconductor laser apparatus is determined on the basis of relationships between respective elements of the semiconductor laser apparatus including a cavity length of the semiconductor laser apparatus and a carrier concentration of an upper cladding layer of the semiconductor laser apparatus and a photoelectric conversion efficiency or electric drive power of the semiconductor laser apparatus, for optical output power to be constant as a parameter, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power. An exemplary vicinal value is preferably within 10% of the minimum of the drive power and within 10% of the maximum of the conversion efficiency, and more preferably within 6% thereof, and most preferably within 3% thereof.
According to the first aspect of the invention, by implementation of a semiconductor laser apparatus wherein a respective element value of the semiconductor laser apparatus is determined on the basis of relationships between respective elements of the semiconductor laser apparatus including a cavity length of the semiconductor laser apparatus and a carrier concentration of an upper cladding layer of the semiconductor laser apparatus and a photoelectric conversion efficiency or electric drive power of the semiconductor laser apparatus, for optical output power to be constant as a parameter, so that the electric drive power is vicinal to a minimum thereof or the photoelectric conversion efficiency is vicinal to a maximum thereof in correspondence to a desirable optical output power, it is enabled to obtain an desirable optical output power in a range over 50 mW, with a photoelectric conversion efficiency in a vicinity of a maximum or electric drive power in a vicinity of a minimum.
According to the second aspect of the invention, th
Kimura Toshio
Tsukiji Naoki
Yoshida Junji
Nguyen Dung T
Sheppard Mullin Richter & Hampton LLP
The Furukawa Electric Co. Ltd.
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