Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-12-26
2004-02-10
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06690698
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 transverse 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.
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
′
=
(
2
m
+
1
)
λ
4
{
n
b
′2
-
n
c
′2
+
(
λ
2
d
c
′
)
2
}
1
2
(
1
)
d
b2
′
=
m
λ
2
{
n
b
′2
-
n
c
′2
+
(
λ
2
d
c
′
)
2
}
1
2
(
2
)
The semiconductor laser elements disclosed in U.S. Pat. No. 5,606,570 have a structure which requires a regrowth technique. According to the structure, InGaP, InAlP, or GaAs layers are exposed at the surface as a base of the regrowth at the time 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 practicable.
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.
Another object of the present invention is to provide a process for producing 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.
(1) According to the first aspect of 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 In
0.49
Ga
0.51
P or Al
z1
Ga
1-z1
As of the first conductive type, where 0.2≦z1≦0.8; a lower optical waveguide layer formed above the lower cladding layer and made of GaAs 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
x3
Ga
1-x3
As
1-y3
P
y3
where 0.49y3≦x3≦0.4 and 0≦y3≦0.1; an upper optical waveguide layer formed above the compressive-strain quantum-well active layer and made of GaAs which is undoped or a second conductive type; a first etching stop layer made of In
x8
Ga
1-x8
P of the second conductive type and formed above the upper optical waveguide layer other than stripe areas of the upper optical waveguide 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 extend in an oscillation direction of a laser resonator; a first current confinement layer made of GaAs of the first conductive type and formed above the first etching stop layer; a second etching stop layer made of In
x9
Ga
1-x9
P of the first conductive type or the second conductive type and formed above the first current confinement layer and ones of the stripe areas of the upper optical waveguide layer corresponding to the low-refractive-index regions, where 0≦x9≦1; a second current confinement layer made of Al
z1
Ga
1-z1
As of the first conductive type and formed above the second etching stop layer; an upper cladding layer made of Al
z1
Ga
1-z1
As of the second conductive type and formed above the second current confinement layer and at least one of the stripe areas of the upper optical waveguide layer corresponding to the at least one current injection region; and a contact layer made of GaAs of the second conductive type and formed above the upper cladding layer.
Preferably, the semiconductor laser element according to the first aspect of the present invention may also have one or any possible combination of the following additional features (i) to (iv).
(i) The semiconductor laser element according to the first aspect of the present invention may further comprise a cap layer made of GaAs of the first conductive type or the second conductive type and formed on the second current confinement layer made of Al
z1
Ga
1-z1
As of the first conductive type.
(ii) The semiconductor laser element according to the first aspect of the present invention may further comprise a GaAs layer of the second conductive type and formed between the first etching stop layer and the first current confinement layer, where the first etching stop layer is made of In
x8
Ga
1-x8
P of the second conductive type, and the first current confinement layer is made of GaAs of the first conductive type.
(iii) The semiconductor laser element according to the first aspect of the present invention may further comprise an InGaAs quantum-well layer formed at a mid-thickness of the first current confinement layer, where the InGaAs quantum-well layer has a bandgap smaller than the bandgap of the active layer.
(iv) It is preferable that the width of each of the at least one current injection region is 3 micrometers or greater.
(2) According to the second aspect of the present invention, there is provided a process for producing a semiconductor laser element, comprising the steps of: (a) forming above a GaAs substrate of a first conductive type a lower cladding layer made of In
0.49
Ga
0.51
P or Al
z1
Ga
1-z1
As of the first conductive type, where 0.2≦z1≦0.8; (b) forming above the lower cladding layer a lower optical waveguide layer made of GaAs which is undo
Fuji Photo Film Co. , Ltd.
Ip Paul
Sughrue & Mion, PLLC
Zahn Jeffrey N
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