Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-09-29
2001-02-27
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S046012
Reexamination Certificate
active
06195373
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor laser, and more particularly to a composition of a semiconductor layer for forming a index optical waveguide semiconductor laser.
2. Description of the Related Art
Recently semiconductor lasers have come to be wide used in light communication, optical discs, laser printers and the like. Advent of high output semiconductor lasers not lower than 1W has realized application of semiconductor lasers to sublimation of dye by use of a laser spot as a high density heat source or to image forming, processing of material or soldering by use of laser ablation.
There have been made various attempts to make more stable a semiconductor laser and to increase output power of a semiconductor laser. For instance, as disclosed in “Applied Physics Letters”, Vol. 69(1996) pp. 1532 to 1534, there has been proposed a 980 nm band semiconductor laser comprising an n-InGaP clad layer, an InGaAsP optical waveguide layer, an InGaAs strained double quantum-well active layer, an InGaAsP optical waveguide layer, a p-InGaP clad layer, and a p-GaAs cap layer formed on an n-GaAs substrate. In this semiconductor laser, the thicknesses of the optical waveguide layers are increased to reduce internal loss and to reduce the density of light in the active layer, thereby obtaining a light output of 8W for a stripe width of 100 &mgr;m.
As a semiconductor laser in which the output power is increased by increasing thickness of the optical waveguide layer, there have been reported in “SPIE Proc., Vol. 3001(1997), pp. 7-12” a semiconductor laser having an active layer formed of InGaAsP and an optical waveguide layer and a clad layer formed of InGaAlP and a 810 nm band semiconductor laser which comprises an InGaAsP active layer, an InGaP optical waveguide layer, an n-In
0.5
Ga
0.25
Al
0.25
P clad layer, a p-In
0.5
Ga
0.25
Al
0.25
P first upper clad layer, a p-In
0.5
Ga
0.45
Al
0.05
P second upper clad layer, and a p-AlGaAs carrier blocking layer disposed in a boundary region of the first and second upper clad layers.
In a semiconductor laser, an index optical waveguide structure such as a ridge structure is generally formed in order to control the fundamental transverse mode. The index optical waveguide structure is formed by etching the epitaxial layer on each side of the ridge stripe up to a certain depth of the upper clad layer or the optical waveguide layer with the upper clad layer or the optical waveguide layer left there in a certain thickness. Since the oscillation mode is governed by the thickness of the upper clad layer or the optical waveguide layer left there, the depth of etching must be carefully controlled. However in the high output semiconductor lasers described above, it is very difficult to stop etching at a desired depth in forming the index optical waveguide structure due to their arrangement of the semiconductor layers. Accordingly, it is difficult to manufacture a high output semiconductor laser oscillating in a controlled transverse mode at a high repeatability.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a high output power index optical waveguide semiconductor laser which oscillates in a controlled transverse mode and can be manufactured at a high repeatability.
In accordance with a first aspect of the present invention, there is provided an index optical waveguide semiconductor laser comprising a lower clad layer, a lower optical waveguide layer, an active layer, an upper optical waveguide layer and an upper clad layer superposed one on another in this order on a GaAs substrate, wherein the improvement comprises that
each of the upper and lower clad layers and the upper and lower optical waveguide layers is of a composition which matches with the GaAs substrate in lattice,
the upper optical waveguide layer comprises an In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y
2P
y2
(1≧y2≧0.8) optical waveguide layer and a Ga
1−z1
Al
z1
As optical waveguide layer formed on the upper surface of the In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y
2P
y2
optical waveguide layer, and
the difference in the refractive index to light at the oscillation wavelength of the semiconductor laser between the In
x2
(Al
z
2Ga
1−z
2)
1−x2
As
1−y2
P
y2
optical waveguide layer and the Ga
1−z1
Al
z1
As optical waveguide layer is not larger than 2% of the larger of the refractive indexes of the optical waveguide layers.
The expression “the difference in the refractive index to light at the oscillation wavelength of the semiconductor laser between the In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y2
P
y2
optical waveguide layer and the Ga
1−z1
Al
z1
As optical waveguide layer is not larger than 2% of the larger of the refractive indexes of the optical waveguide layers” should be interpreted to mean that the indexes of the optical waveguide layers to light at the oscillation wavelength of the semiconductor laser are equal to each other or slightly differ from each other (difference therebetween is 2% at most).
Preferably the difference in the refractive index is not larger than 1% of the larger of the refractive indexes of the optical waveguide layers.
In accordance with a second aspect of the present invention, there is provided an index optical waveguide semiconductor laser comprising a lower clad layer, a lower optical waveguide layer, an active layer, an upper optical waveguide layer and an upper clad layer superposed one on another in this order on a GaAs substrate, wherein the improvement comprises that
each of the upper and lower clad layers and the upper and lower optical waveguide layers is of a composition which matches with the GaAs substrate in lattice,
the upper optical waveguide layer comprises a Ga
1−z1
Al
z1
As optical waveguide layer and an In
x6
(Al
z6
Ga
1−z6
)
1−x6
P optical waveguide layer formed on the upper surface of the Ga
1−z1
Al
z1
As optical waveguide layer, and
the difference in the refractive index to light at the oscillation wavelength of the semiconductor laser between the Ga
1−z1
Al
z1
As optical waveguide layer and the In
x6
(Al
z6
Ga
1−z6
)
1−x6
P optical waveguide layer is not larger than 2% of the larger of the refractive indexes of the optical waveguide layers.
In accordance with a third aspect of the present invention, there is provided an index optical waveguide semiconductor laser comprising a lower clad layer, a lower optical waveguide layer, an active layer, an upper optical waveguide layer and an upper clad layer superposed one on another in this order on a GaAs substrate, wherein the improvement comprises that
each of the upper and lower clad layers and the upper and lower optical waveguide layers is of a composition which matches with the GaAs substrate in lattice,
the upper optical waveguide layer comprises an In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y2
P
y2
(1≧y2≧0.8) optical waveguide layer, a Ga
1−z1
Al
z1
As optical waveguide layer formed on the upper surface of the In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y2
P
y2
optical waveguide layer, and an In
x6
(Al
z6
Ga
1−z6
)
1−x6
P optical waveguide layer formed on the upper surface of the Ga
1−z1
Al
z1
As optical waveguide layer,
the difference in the refractive index to light at the oscillation wavelength of the semiconductor laser among the In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y2
P
y2
optical waveguide layer, the Ga
1−z1
Al
z1
As optical waveguide layer and the In
x6
(Al
z6
Ga
1−z6
)
1−x6
P optical waveguide layer is not larger than 2% of the largest of the refractive indexes of the three optical waveguide layers.
The expression “the difference in the refractive index to light at the oscillation wavelength of the semiconductor laser among the In
x2
(Al
z2
Ga
1−z2
)
1−x2
As
1−y2
P
y2
optical waveguide layer, the Ga
1−z1
Al
z1
As optical w
Davie James W.
Fuji Photo Film Co. Ltd
Sughrue Mion Zinn Macpeak & Seas, PLLC
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