Coherent light generators – Particular active media – Insulating crystal
Reexamination Certificate
2003-05-05
2004-02-03
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Insulating crystal
C372S020000, C372S023000, C372S092000, C372S099000, C372S101000, C372S102000, C372S103000
Reexamination Certificate
active
06687275
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to semiconductor cavity lasers, and more particularly, the present invention provides an improved cavity structure that uses a plurality of mirrors to separate reflection wavelengths.
2. Description of the Prior Art
Due to an arrival of an information age, using a broadband network and wavelength-division multiplexing (WDM) to provide high-capacity, high-speed data transmission has already become a trend. Traditionally, fiber-optic communication systems use wavelengths of 1.55 &mgr;m and 1.3 &mgr;m, because fiber loss and dispersion loss are minimized in these bands. Currently, a latest development in fiber-optic technology allows a significant reduction in hydroxyl absorption at 1.4 &mgr;m. Thus, fiber-optic communications already anticipate a bandwidth at 300 nm. So, it is imperative to provide a tunable laser source.
Since beginning research of multiple quantum well structures in 1974, design of super-crystalline structure semiconductor lasers has become a separate development trend. A high efficiency, a low threshold current, and an adjustable wavelength suggest the semiconductor lasers as optimal laser light sources for use in advanced optical systems. Recently, developments in multiple quantum well laser technology already provide very wideband light sources. With an addition of an external wideband tunable technology, a single-oscillation laser can be selected, e.g. a semiconductor optical amplifier. However, tunability of the semiconductor optical amplifier is limited by the traditional resonant cavity structure.
Currently there are many tunable wavelength laser technologies, such as a Fabry-Perot (FB) wavelength filter, a diffraction grating filter, a rotated thin-film filter, an electro-optic tunable filter, and a tunable fiber-grating filter. These wavelength tuning technologies are typically used for singl-wavelength oscillation, and aside from using grating technologies, are limited to a wavelength tuning range of under 100 nm. However, if the tunable cavity semiconductor laser uses a diffraction grating technology, the tunable range increases to over 200 nm.
Please refer to
FIG. 1
, which is a diagram of a resonant cavity structure
100
of a prior art tunable integrated semiconductor laser. The resonant cavity structure
100
comprises a grating
10
, a collimating lens
11
, and an FP semiconductor laser or a semiconductor optical amplifier (SOA)
13
. The FP semiconductor laser or the SOA
13
comprises a waveguide
15
for propagating light waves, a first end facet and a second end facet. The first end facet is coated with an anti-reflective layer
12
, and the second end facet has a cleavage. This type of resonant cavity structure is only suitable for single-wavelength oscillation design. After the laser light is produced by the FP laser or the SOA
13
, the laser light is emitted from the anti-reflective layer
12
, then the collimating lens
11
focuses the laser light into one parallel beam incident on the optical grating
10
. A relationship between an angle of incidence &thgr; i and an angle of reflection &thgr; r of the beam can be given as:
sin(&thgr;
r
)=sin(&thgr;
i
)+m&lgr;/&Lgr;
where &lgr; is a laser wavelength, &Lgr; is a grating line spacing, and m is an integer.
When the selected laser wavelength is tuned to fit the condition &thgr; i=&thgr; r, the selected incident beam follows a path of the incident beam to reflect back to the collimating lens
11
, then pass through the anti-reflective layer
12
into the FP laser or the SOA
13
. This forms a single-wavelength oscillation path, and the output laser beam
14
is emitted through the second end face of the FP laser or the SOA
13
.
Please refer to
FIG. 2
, which is a second prior art cavity structure
200
of a tunable semiconductor laser. The cavity structure
200
comprises a grating
20
, a collimating lens
21
and an FP semiconductor laser or an SOA
23
, which comprises a waveguide
26
for propagating light beams, a first end facet and a second end facet. The first end facet is coated with an anti-reflective layer, and the second end facet is coated with a high reflective layer
24
. This type of resonant cavity structure is limited for use in single-wavelength oscillation designs. Unlike above, the laser beam is output by way of the grating
20
, however the working principles are similar. After the laser light is produced by the FP laser or the SOA
23
, the laser light may be reflected back by the high reflective layer
24
, or directly pass through the anti-reflective layer
22
. The laser light then passes the collimating lens
21
, which collimates the laser light to become a parallel beamincident on the grating
20
. The grating
20
thus separates the laser beam to become specific wavelength beam with an appropriate angle.
Please refer to FIG.
3
. In a case of the laser beam being a dual-wavelength or multi-wavelength light source, the above two prior art tunable semiconductor laser cavity structures no longer fulfill the requirements.
FIG. 3
is a diagram of a third prior art dual-wavelength resonant cavity structure
300
for a tunable semiconductor laser. The structure
300
comprises an optical grating
30
, a first collimating lens
31
, an SOA
32
, a second collimating lens
33
, a convex lens
34
, a light tuning slit plate
35
, and a reflector
36
. The slit plate comprises a first slit
301
and a second slit
302
. The optical grating
30
is set at a focal point of the convex lens
34
. After the laser light source is produced by the SOA
32
, the scattered light is sent through the collimating lens
31
to be focused into a parallel light beam incident on the grating
30
. After being separated by the grating
30
, a short-wavelength light beam
37
and a long-wavelength light beam
38
are produced, which are then sent through the convex lens
34
to become parallel light respectively incident upon the first and second slits
301
,
302
of the tuning slit plate
35
. The beams are reflected back by the reflectors
36
, thus forming two laser light resonance paths. A laser light beam
39
is sent through the second collimating lens
33
and output. Thus, the output laser beam is a dual-wavelength beam formed of the short-wavelength beam
37
and the long-wavelength beam
38
. If the tuning slit plate
35
comprises further slits, by the same principle, a multi-wavelength laser beam could be produced. However, in the tunable semiconductor laser dual-wavelength cavity structure
300
, it is difficult for the convex lens
34
to be accurately placed at a desired location between the optical grating
30
and the reflectors
36
. If there is the slightest error in the position of the convex lens
34
, not to mention the laser beam being incident on a non-ideal point on the grating
30
, in either case it becomes impossible to collimate the two beams of different wavelengths. So, just using the single reflector
36
to ideally reflect the non-parallel light beams back to the resonance path is not possible. This causes non-uniform lasing loss in the dual-wavelength resonance cavity structure, and could be extended analogously to a multi-wavelength structure.
SUMMARY OF INVENTION
Thus, it is an objective of the claimed invention to provide a multi-wavelength tunable semiconductor laser structure that uses multiple reflectors to solve the above problems.
The structure of the claimed invention has a semiconductor optical amplifier (SOA), an optical grating, a convex lens, a light-tuning slit plate, and a plurality of tunable reflectors. The SOA has a first and a second end, the first end coupled to a resonance cavity, and the second end being a laser light output. The slit plate has a plurality of slits. The optical grating is set on a resonance path between the first end of the SOA and the slit plate. The slit plate is set in front of reflective sides of the plurality of tunable reflectors. The reflective sides of the plurality of tunable reflectors are aligned with the
Arima Optoelectronics Corp.
Flores-Ruiz Delma R.
Hsu Winston
Leung Quyen
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