Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-04-10
2002-10-01
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S096000
Reexamination Certificate
active
06459715
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor lasers. In particular, the present invention relates to master oscillator grating coupled power amplifiers (MOGCPAs).
BACKGROUND
Master oscillator power amplifiers (MOPAs), as shown in
FIG. 1
, typically include a semiconductor Distributed Feedback (DFB) laser diode
101
acting as a master oscillator optically coupled to a tapered optical power amplifier
102
. The diode laser and amplifier are essentially a single unit with an integrated optical alignment.
MOPAs are known to have potential to provide both high power and a diffraction-limited single-mode output. MOPA designs that produce a high-power single-mode output, however, have a variety of weaknesses. For example, to achieve a single-mode output, the master-oscillator section of the device is very narrow. This often results in the device exhibiting a large lateral beam divergence, thereby requiring an astigmatic lens for practical use. For example, known MOPA devices can exhibit as much as 15 to 20 degrees beam divergence in the lateral direction, creating at least two problems. First, the divergent beam with a wide output aperture requires complicated focusing optics. Second, the divergent beam propagating in the amplifier section requires an amplifier section with a wide aperture. Since the length of the tapered section must not be shorter than 1 mm to provide the amplification, the output aperture can not be narrower than 50-350 &mgr;m. Additionally, known designs also tend to exhibit self-focusing and filamentation problems that limit the level of diffraction-limited power and degrade device stability.
Variations of MOPAs have been conceived, but all contain unacceptable shortcomings.
For example,
FIG. 2
is a schematic diagram detailing a Master-Oscillator Deflector-Amplifier Grating for Surface Emission (GSE). In this figure, a laser beam generated in master-oscillator section
201
couples directly into deflector-amplifier section
202
, which lies along the same axis as master-oscillator section
201
. Deflector-amplifier section
202
contains tilted Bragg grating deflector
204
. Deflector-amplifier section
202
is optically coupled to GSE section
203
through tilted grating
204
, which scatters the laser beam into GSE section
203
. GSE section
203
has a grating that scatters the generated laser beam in the direction perpendicular to the structure plane. Thus, this configuration utilizes three regions, with a coupling grating found inside deflector-amplifier section
202
, and light is emitted perpendicular to the direction of propagation through the amplifier section. This apparatus, however, has the drawback that, to maintain single-mode operation, deflector-amplifier amplifier section
202
must be the same width as master-oscillator section
201
, thereby limiting output.
FIGS. 3A and 3B
is a configuration of the previously-discussed apparatus in which power is amplified by the addition of post amplifier
302
. This configuration has the drawback that, because of the refractive index step at the interface between post amplifier
302
and GSE
303
, multimode lasing in the direction perpendicular to the axes of the deflector-amplifier section occurs.
FIG. 4
is an apparatus that employs the basic design shown in
FIG. 2
, but includes beam splitters between master-oscillator section
401
and deflector-amplifier sections
402
a
-
402
d
. The splitters allow for additional GSE sections
403
a
-
403
d
. Power output is not improved, however, because beam splitters
401
a
divide the available energy and introduce additional losses.
FIG. 5
is the same as the apparatus discussed in
FIG. 2
, except that GSE
503
is rotated at an angle &OHgr; relative to deflector-amplifier section
502
. This configuration has drawbacks similar to the configuration displayed in FIG.
2
.
FIG. 6
displays a variety of embodiments that include laser or lasers
601
and GSE
602
. These configurations do not include a broad-contact “power supplying” section, and are not limited to a single-mode output.
Thus, a need exists for a type of MOPA with low lateral beam divergence, and which is stable at high power output with a narrow output aperture.
SUMMARY OF THE INVENTION
To alleviate the problems inherent in known MOPAs, the present invention introduces a master oscillator grating coupled power oscillator (MOGCPA) with a power-oscillator section at an angle to the optical cavity in the master-oscillator section.
In one embodiment of the present invention, the MOGCPA contains a single-mode-master-oscillator section with a waveguide defined by a first end and a second end, the first end including a first distributed Bragg reflector mirror, and the second end including a second distributed Bragg reflector mirror, the single-mode-master-oscillator section having a first longitudinal axis. The MOGCPA additionally contains a broad-contact-amplifier section coupled to said single-mode-master-oscillator section by a coupling grating, said broad contact amplifier section including a reflection side, an output side and a second longitudinal axis, the second longitudinal axis being at an angle approximately (90°−&bgr;) to said first longitudinal axis, &bgr; being in a range between 0° and approximately 20°.
REFERENCES:
patent: 5103456 (1992-04-01), Scifres et al.
patent: 5440576 (1995-08-01), Welch et al.
Connolly John Charles
DiMarco Louis Anthony
Garbuzov Dmitri Zalmanovich
Khalfin Viktor Borisovich
Duane Morris LLP
Leung Quyen
Plevy Arthur L.
Princeton Lightwave Inc.
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