Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-09-26
2003-12-09
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S046012, C372S045013
Reexamination Certificate
active
06661821
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser element including an ARROW (Antiresonant Reflecting Optical Waveguide) structure. In particular, the present invention relates to a semiconductor laser element including an ARROW structure and emitting laser light in the 980 nm band.
2. Description of the Related Art
A reliable high-power semiconductor laser element which emits a high-quality, diffraction-limited beam is required for use as a light source in exciting an optical fiber amplifier.
U.S. Pat. No. 5,606,570 discloses a semiconductor laser element having an ARROW structure as a semiconductor laser element which can emit a high-output-power, diffraction-limited laser beam in the 980 nm band. The disclosed semiconductor laser element includes an InGaAs active layer and an InGaAlP current confinement layer, and uses GaAs as a medium having a high refractive index. The ARROW structure is a structure for confining light in core regions. The disclosed ARROW structure includes a plurality of core regions having a low equivalent (effective) refractive index, first high-refractive-index regions which have a high equivalent refractive index and are arranged between the plurality of core regions and on the outer sides of the plurality of core regions, low-refractive-index regions which have an equivalent refractive index approximately identical to that of the plurality of core regions and are arranged on the outer sides of the outermost ones of the high-refractive-index regions, and second high-refractive-index regions which have a high equivalent refractive index and are arranged on the outer sides of the low-refractive-index regions. The first high-refractive-index regions behave as reflectors of light in the fundamental mode, and the low-refractive-index regions suppress leakage of light. Thus, the semiconductor laser element can be controlled so as to operate in the fundamental transverse mode.
In addition, it is reported that a preferable value of the width d
b1
′ of each of the outermost ones of the first high-refractive-index regions is determined in accordance with the equation (1), a preferable value of the width d
b2
′ of each of the first high-refractive-index regions arranged between the plurality of core regions is determined in accordance with the equation (2), and a preferable value of the width of each of the low-refractive-index regions is d
c
′/2, where d
c
′ is the width of each of the plurality of core regions. In the equations (1) and (2), &lgr; is the oscillation wavelength, n
c
′ is the equivalent refractive index of the plurality of core regions, and n
b
′ is the equivalent refractive index of the first high-refractive-index regions.
d
b1
′
=
3
λ
4
{
n
b
′2
-
n
c
′2
+
(
λ
2
d
c
′
)
2
}
1
2
(
1
)
d
b2
′
=
λ
2
{
n
b
′2
-
n
c
′2
+
(
λ
2
d
c
′
)
2
}
1
2
(
2
)
In order to produce an ARROW structure, it is necessary to use a regrowth technique. However, in the semiconductor laser element disclosed in U.S. Pat. No. 5,606,570, GaAs and InGaP layers (or InAlP, GaAs, and InGaP layers) are exposed at the surface as a base of the regrowth. Therefore, P-As interdiffusion occurs at the exposed surface during a process of raising temperature for the regrowth, and thus the regrowth is likely to become defective. As a result, the above semiconductor laser element is not actually used. Further, since the difference in the bandgap between the optical waveguide layer and the active layer is small, the above semiconductor laser element has poor temperature characteristics.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor laser element which includes an ARROW structure and is reliable in a wide output power range from low to high output power levels.
(I) According to the present invention, there is provided a semiconductor laser element comprising: a GaAs substrate of a first conductive type; a lower cladding layer formed above the GaAs substrate and made of Al
x
Ga
1−x
As of the first conductive type, where 0.57≦x≦0.8; a lower optical waveguide layer formed above the lower cladding layer and made of In
0.49
Ga
0.51
P which is undoped or the first conductive type; a compressive-strain quantum-well active layer formed above the lower optical waveguide layer and made of undoped In
x1
Ga
1−x1
As
1−y1
P
y1
, where 0.49y1<x1≦0.4 and 0≦y1≦0.1; an upper optical waveguide layer formed above the compressive-strain quantum-well active layer and made of In
0.49
Ga
0.51
P which is undoped or a second conductive type; a first etching stop layer formed above the upper optical waveguide layer and made of GaAs of the second conductive type; a second etching stop layer made of In
x8
Ga
1−x8
P of the second conductive type and formed above the first etching stop layer other than stripe areas of the first etching stop layer corresponding to at least one current injection region and low-refractive-index regions located on outer sides of the at least one current injection region and separated from the at least one current injection region or outermost ones of the at least one current injection region by a predetermined interval, where 0≦x8≦1, and the stripe areas of the first etching stop layer extend in a direction of a laser resonator; a first current confinement layer made of GaAs of the first conductive type and formed above the second etching stop layer; a third etching stop layer made of In
x9
Ga
1−x9
P of the second conductive type and formed over the first current confinement layer and the stripe areas of the first etching stop layer, where 0≦x9≦1; a fourth etching stop layer made of GaAs of the second conductive type and formed above the third etching stop layer other than at least one stripe area of the third etching stop layer corresponding to the at least one current injection region; a second current confinement layer made of In
0.5
(Ga
1−z
Al
z
)
0.5
P of the first conductive type and formed above the fourth etching stop layer, where 0.1≦z≦1; a first upper cladding layer of the second conductive type, formed above the second current confinement layer and the at least one stripe area of the third etching stop layer, and made of one of AlGaAs and In
0.5
(Ga
1−z
Al
z
)
0.5
P, where 0.1≦z≦1; and a contact layer made of GaAs of the second conductive type and formed above the first upper cladding layer.
The first conductive type is different in the polarity of carriers from the second conductive type. That is, when the first conductive type is n type, and the second conductive type is p type.
In addition, the term “undoped” means that a material is not doped with any conductive impurity.
Preferably, the semiconductor laser element according to the present invention may also have one or any possible combination of the following additional features (i) to (iv).
(i) Each of the at least one current injection region may have a width equal to or greater than 3 micrometers.
(ii) The semiconductor laser element according to the present invention may further comprise a second upper cladding layer formed between the upper optical waveguide layer and the first etching stop layer, and made of a material having identical composition and an identical conductive type to the first upper cladding layer.
(iii) The first current confinement layer may include first and second sublayers made of GaAs of the first conductive type, and a quantum-well layer formed between the first and second sublayers and made of an InGaAs material which has a smaller bandgap than the bandgap of the compressive-strain quantum-well active layer.
(iv) The semiconductor laser element according to the present invention may further comprise a lower barrier layer formed between the lower optical waveguide layer and the compressive-strain quantum-well active layer, and an upper barrier layer formed between the upper op
Fuji Photo Film Co. , Ltd.
Nguyen Dung
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