Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-04-20
2003-04-01
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
Reexamination Certificate
active
06542532
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a semiconductor laser device. More specifically, the present invention is related to a semiconductor laser device having high output power/high efficiency characteristics, and also superior single-mode characteristics.
2. Description of the Related Art
As a method for optically coupling a semiconductor optical waveguide device (namely, one optical function device) to a single-mode optical fiber (namely, the other optical function device), a semiconductor laser diode and a semiconductor switch are employed. In this “Butt-coupling” method, an edge surface of an optical waveguide device directly abuts against an optical fiber.
However, in accordance with this “Butt-coupling” method, since the spot sizes of the laser light propagated through the optical waveguides are different from each other, such a coupling loss indicative of the loss in the waveguide light amount would occur at the direct abutting portion.
Normally, a spot size (mode diameter) of a laser beam projected from a semiconductor device is selected to be on the order of 1 micrometer. Also, normally, a spot size of a laser beam for an optical fiber is selected to be approximately 5 micrometers. As a result, a coupling loss occurred in the “Butt-coupling” between the semiconductor optical device and the optical fiber will become approximately 10 dB.
Conventionally, as a method for reducing a coupling loss, a lens is employed for converting spot sizes of laser beams.
However, as to the coupling method with using such a lens, since tolerance in the lens alignment is small, it is practically difficult to assemble this lens with the semiconductor optical device. As a consequence, manufacturing cost of the respective modules would be increased.
In particular, very recently, application fields of semiconductor laser diodes are rapidly extended from ground transmission systems to other systems such as a subscriber system, a LAN (local area network) system, and a data link system. Under such a circumstance, a large number of semiconductor laser diode modules manufactured in low cost are necessarily required. As a consequence, total numbers of components required when one semiconductor laser diode itself is manufactured are desirably reduced. Furthermore, since the major portion of the manufacturing cost of these modules is caused by the difficult assembling work, the optical fiber is coupled with the semiconductor laser diode by employing an easy assembly by a passive alignment.
Based upon the above-described technical aspects, various sorts of optical coupling devices and various types of light sources in which optical coupling devices are integrated with semiconductor laser diodes have been developed.
For instance, the beam spot-size expanded laser diode with the laterally tapered active stripe is described in “International Conference on Indium Phosphide and Related Material, Conference Proceedings” pages 657 to 660, in 1997. In this beam spot-size expanded laser diode, the entire resonator is composed of the active layer region. And this beam spot-size expanded laser diode can oscillate laser light with the superior temperature characteristic and also the high convergence rate.
FIG. 1A
illustratively shows the structure of the above-described beam spot-size expanded laser diode with the lateral tapered active stripe.
Referring now to
FIG. 1A
, the beam spot-size expanded laser diode has a following-described structure.
A P type InP layer
721
and an InGaAsP active layer
701
are formed on a P type InP substrate
708
.
An N type InP layer
714
is formed on a P type InP layer
721
.
A P type InP layer
712
is formed on an N type InP layer
714
.
An N type InP layer
710
is formed on the entire surface of the element.
Furthermore, a film
703
having a low reflective power is provided on a front surface of the beam spot-size expanded laser diode.
Also, a film
702
having a high reflective power is provided on a rear surface of the beam spot-size expanded laser diode.
FIG. 1B
illustratively represents the shape of the active layer
701
contained in this beam spot-size expanded laser diode with the lateral tapered active stripe.
The active layer
701
includes an active layer region
705
and a tapered active layer region
706
. The tapered active layer region
706
has such a structure the width of the tapered active layer region
706
is narrowed at a region near the laser light radiation plane.
Referring now to FIG.
1
A and
FIG. 1B
, this beam spot-size expanded laser diode with the lateral tapered active stripe owns such a structure that the width of the active layer
701
is narrowed at a region near the laser light radiation plane.
In this semiconductor laser diode, since the entire resonator corresponds to the active region, it is possible to relatively shorten the length of this semiconductor laser. As a result, this semiconductor laser diode owns an advantageous structure to have a high convergence rate. Also, this specific semiconductor laser diode may be manufactured by utilizing the same manufacturing steps for the semiconductor laser diode having the conventional uniform active layer width.
In the beam spot-size expanded laser diode with the laterally tapered active stripe, when the length of the tapered active layer region
706
is shortened while maintaining the length of the resonator at a constant value, the volume of the active layer
701
is increased. As a result, the gain of this semiconductor laser diode is increased to reduce the threshold current value and the operating current under high temperatures. Also, the shorter the length of this tapered active layer region
706
becomes, the higher the coupling degree to the radiation mode is increased to reduce the coupling efficiency of this semiconductor laser diode with respect to the optical fiber.
Other conventional semiconductor laser devices have been described as follows.
Japanese Laid-open Patent Application (JP-A-Heisei 10-22577) describes “LIGHT EMITTING SEMICONDUCTOR DEVICE”. This light emitting semiconductor (laser diode) device is equipped with the beam spot-size conversion structure, and is capable of blocking such a phenomenon that the laser light leaked out from the core in the spot-size conversion region is returned to the gain region of this laser diode. Concretely speaking, this laser diode is featured by having the reflection structure capable of reflecting the scattered laser light in the vicinity of the spot-size conversion structure and the gain region. This scattered laser light is leaked out from the core and then is entered into the gain region.
Also, Japanese Laid-open Patent Application (JP-A-Heisei 9-61652) discloses “SEMICONDUCTOR OPTICAL WAVEGUIDE AND MANUFACTURING METHOD THEREOF”. In the semiconductor optical waveguide and the manufacturing method thereof, when the optical element such as the semiconductor laser device is coupled to another optical element, or the optical fiber without using the lens system, the coupling efficiency can be increased. The structure of this semiconductor optical waveguide represents such a tapered shape that the thickness of the core layer of the optical waveguide is continuously changed in an exponential manner.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-explained problems.
Therefore, an object of the present invention is to provide a semiconductor laser device capable of realizing a high coupling efficiency between this semiconductor laser device and an optical fiber under a condition that this semiconductor laser device has a tapered structure of a short length.
Another object of the present invention is to provide a semiconductor laser device capable of achieving a low threshold value and a high coupling efficiency at the same time under high temperature.
In order to achieve an aspect of the present invention, a semiconductor laser device includes an electron carrying layer, an active layer, and a hole carrying layer. The electron carrying layer is
Hayes & Soloway P.C.
Leung Quyen
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