Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2000-09-11
2003-11-18
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S098000, C257S103000, C372S049010, C372S050121
Reexamination Certificate
active
06649938
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to quantum electronics, specifically to high-power multimode, monomode, and/or single-frequency radiation sources, and in particular to semiconductor optical amplifiers.
BACKGROUND OF THE INVENTION
Traditionally, a semiconductor optical amplifier (SOA) consists of a master source of input radiation whose output is optically coupled by an optical system to the input of an amplifying component (AC). See S. O'Brien et al.,
IEEE J. of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2052-2057, and J. P. Donnelly et al.,
IEEE Phot. and Technology Letters
(1996), Vol. 8, pp. 1450-1452). The optical signals usually are spontaneous, superluminescent, or laser radiation. By virtue of the specific features of a SOA, such as small size, high gain per unit length, high efficiency, potentially low cost, integrability into optoelectronic circuits, etc., the SOA unquestionably has great prospects for use both in the design of complex communications networks, particularly branched networks, and in the development of efficient high-power radiation sources.
An SOA in a discrete implementation is known that includes a master source of input radiation that is input, when the amplifier is in operation, at an input angle &dgr; into an AC optically coupled to the source. See L. Goldberg et al.,
IEEE J. of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042. The AC is implemented on the basis of a semiconductor laser heterostructure that contains an active layer with a refractive index n
a
and a bandgap E
a
(eV) positioned between two cladding layers, in each of which there is at least one sublayer. The active gain region is implemented by using barrier regions to form a mesa strip that widens linearly from its initial width W
in
of 10 &mgr;m at the input face of the active gain region, to a final width W
out
of 160 &mgr;m at the output face of the active gain region. The length L
AGR
of the SOA was 1500 &mgr;m. Note that the longitudinal axis of the active gain region, which lies in the active layer and is the optical gain axis of the AC, is located on the same optical axis as that of the master source and the optical system. The method of inputting the input radiation into the active gain region and of outputting radiation therefrom after amplification are via an optical facet on the input face of the active gain region and an optical facet on the output face of the active gain region. These optical facets are conditionally referred to as first optical facets and have antireflective coatings applied whose reflection coefficient, R, was in this case R~0.003. The first optical facets are positioned at angles of inclination &psgr;
1
and &psgr;
2
to the plane perpendicular to the optical gain axis, which is referred to as the normal plane. L. Goldberg et al., in
IEEE J. of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042, discloses a device wherein the first optical facets of the AC are parallel to the normal plane. The sizes of the input and output apertures for the AC discussed by L. Goldberg et al. in
IEEE J. of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042 are:
S
in
=d
AGR
W
in
, (1)
and
S
out
=d
AGR
W
out
, (2)
respectively, where d
AGR
is the thickness of the active gain region, which usually does not exceed 1 &mgr;m. Accordingly, for the AC of the SOA disclosed by L. Goldberg et al. in
IEEE J. of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042, S
in
is no more than 10 &mgr;m
2
and S
out
is no more than 160 &mgr;m
2
.
Antireflective coatings applied to the first optical facets of the active gain region are used as a means of suppressing spurious reflections and rereflections of the output signal (SPPI) in the AC shown by L. Goldberg et al. in
IEEE J. Of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042.
The SOA disclosed by L. Goldberg et al.,
IEEE J. Of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042 uses as its master source of input radiation a master laser diode with monomode radiation and a power P
MSout
of 100 mW. The input radiation was focused by the optical system into a spot measuring 1×4 &mgr;m on the first (input) optical facet. In addition, the input beams were input into the active gain region at different input angles &dgr;. This resulted in the input into the amplifying component of an input power P
in
in the AC of 25 mW through the first face of the active gain region.
When an operating current I
work
of 3 A was passed through the AC with a length L
AGR
of 1500 &mgr;m that was disclosed by L. Goldberg et al., in
IEEE J. Of Quantum Electronics
(1993), Vol. 29, No. 6, pp. 2028-2042, 2.5 W of amplified output radiation power, P
out
, was obtained. The input aperture was no larger than 1 &mgr;m. In the vertical plane, the angle of divergence &thgr;
⊥
as with the usual injection-type emitters, was large, i.e., approximately 35°. By vertical plane is meant a plane that passes through the longitudinal axis of the active layer and that is perpendicular to the layers of the laser heterostructure. The output aperture was small, i.e., no more than 1 &mgr;m. The effective angle of divergence &thgr;
∥
of the output radiation in the horizontal plane was 0.29°, which corresponds to the diffraction-limited divergence for the indicated aperture size of 160 &mgr;m. By horizontal plane is meant the plane that is perpendicular to the vertical plane and that passes through the normal of the amplified output radiation front is called horizontal plane. In the known AC in question, the horizontal plane corresponds to the plane of the active layer.
SUMMARY OF THE INVENTION
One preferred embodiment of the present invention comprises a semiconductor optical amplifier comprising a master source of input radiation and an amplifying component optically coupled to the master source. The amplifying component comprises a semiconductor heterostructure that includes an active layer positioned between two cladding layers and an ohmic contact formed to at least one sublayer of the semiconductor heterostructure. The amplifying component also includes an input-output region comprising at least one additional layer on at least one side of the heterostructure. This additional layer adjacent to the heterostructure comprises one or more sublayers having refractive indices n
IORq
and optical loss factors &agr;
IROq
(cm
−1
), where q=1, 2, . . . , p are integers corresponding to the sublayers of the radiation input-output region sequentially counted from their boundaries with the heterostructure,
In the semiconductor optical amplifier, the input-output region is adapted to receive input radiation at an angle of input, &dgr;. Additionally, the angle of the input radiation and the net loss factor &agr;
OR
(cm
−1
) for the amplified radiation flowing from the active layer are such that
0
<
arccos
n
eff
n
IOR1
≤
arccos
n
eff
-
min
n
IOR1
,
and
n
eff
-
min
>
n
min
,
where n
eff
is the effective refractive index of the heterostructure in aggregate with the radiation input-output region, and N
IOR1
is the refractive index of the radiation input-output region, n
eff-min
is the minimum value of n
eff
out of all possible n
eff
for the multiplicity of heterostructures that are of practical interest, in aggregate with radiation input-output regions, and n
min
is the smallest of the refractive indices of the layers of the heterostructure.
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Bogatov Alexandr P.
Drakin Alexandr E.
Kurnyavko Juri V
Shveikin Vasily I.
D-Led Corporation
Knobbe Martens Olson & Bear LLP
Tran Minh Loan
LandOfFree
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