Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-08-13
2003-12-16
Nguyen, Thong (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C372S023000, C372S097000, C372S099000, C372S102000, C398S087000
Reexamination Certificate
active
06665471
ABSTRACT:
BACKGROUND OF THE INVENTION
Incoherently beam combined (IBC) lasers combine the output from an array of gain elements or emitters (typically consisting of semiconductor material, such as GaAlAs, GaAs, InGaAs, InGaAsP, AlGaInAs, and/or the like, which is capable of lasing at particular wavelengths) into a single output beam that may be coupled into, for example, an optical fiber. The gain elements may be discrete devices or may be included on an integrated device. Due to the geometry of IBC lasers, each gain element tends to lase at a unique wavelength.
FIG. 1
depicts a prior art arrangement of components in IBC laser
10
. IBC laser includes emitters
12
-
1
through
12
-N associated with fully reflective surface
11
. Emitters
12
-
1
through
12
-N are disposed in a substantially linear configuration that is perpendicular to the optical axis of collimator
15
(e.g., a lens). Collimator
15
causes the plurality of beams produced by emitters
12
-
1
through
12
-N to be substantially collimated and spatially overlapped on a single spot on diffraction grating
16
. Additionally, collimator
15
directs feedback from partially reflective
17
via diffraction grating
16
to emitters
12
-
1
through
12
-N.
Diffraction grating
16
is disposed from collimator
15
at a distance approximately equal to the focal length of collimator
15
. Furthermore, diffraction grating
16
is oriented to cause the output beams from emitters
12
-
1
through
12
-N to be diffracted on the first order toward partially reflective component
17
, thereby multiplexing the output beams. Partially reflective component
17
causes a portion of optical energy to be reflected. The reflected optical energy is redirected by diffraction grating
16
and collimator
15
to the respective emitters
12
-
1
through
12
-N. Diffraction grating
16
angularly separates the reflected optical beams causing the same wavelengths generated by each emitter
12
-
1
through
12
-N to return to each respective emitter
12
-
1
through
12
-N. Accordingly, diffraction grating
16
is operable to demultiplex the reflected beams from reflective component
17
.
It shall be appreciated that the geometry of external cavity
13
of IBC laser
10
defines the resonant wavelengths of emitters
12
-
1
through
12
-N. The center wavelength (&lgr;
i
) of the wavelengths fed back to the i
th
emitter
12
-i is given by the following equation: &lgr;
i
=A[sin(&agr;
i
)+sin(&bgr;)]. In this equation, A is the spacing between rulings on diffraction grating
16
, &agr;
i
is the angle of incidence of the light from the i
th
emitter on diffraction grating
16
, and &bgr; is the output angle which is common to all emitters
12
-
1
through
12
-N. As examples, similar types of laser configurations are also discussed in U.S. Pat. No. 6,208,679.
To allow emitters
12
-
1
through
12
-N to operate in this type of configuration, anti-reflective coating
14
is applied to the front facet of emitters
12
-
1
through
12
-N. Anti-reflective coating
14
allows substantially all incident light to be transmitted. By applying anti-reflective coating
14
, emitters
12
-
1
through
12
-N lase at the wavelength defined by the feedback wavelengths as discussed above. Specifically, it shall be appreciated that emitters
12
-
1
through
12
-N do not operate as Fabry-Perot emitters, since anti-reflective coating
14
does not provide a partially reflective surface to create internal feedback.
Moreover, anti-reflective coatings of appreciable quality (possessing a reflectivity on the order of 10
−4
) are difficult to achieve on a consistent basis. This is problematic, since anti-reflective coatings of lower quality can significantly diminish performance of an IBC laser.
Additionally, the use of anti-reflective components increases the difficulty of verifying the performance of components in an IBC laser. Specifically, it is desirable to verify the performance of each emitter prior to assembling the entire laser. Performance verification of an emitter array is performed by applying current through the emitters of the emitter array and measuring the output optical power over a period of time. If a very low reflectivity is applied to the front facet, the emitter array will not generate a significant amount of optical power and performance verification is not possible. As a result, the entire IBC laser must be assembled before the various components can be tested. Accordingly, this greatly increases the cost of manufacturing IBC lasers.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a system and method which utilize an incoherently beam combined (IBC) laser. The IBC laser includes a plurality of emitters with each of the emitters possessing a partially reflective surface on their front facet. The partially reflective surface causes resonant wavelengths to be defined. In certain embodiments, the system and method arrange the external cavity and emitter spacings of the IBC laser such that the center feedback wavelength provided to each emitter is an etalon resonant wavelength. In other embodiments, the range of feedback wavelengths is adapted so that it exceeds the free spectral range (the separation in wavelength space between adjacent etalon resonant wavelengths).
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Farmer Jason N.
Karlsen Scott R.
Pratt Mark R.
Fulbright & Jaworski L.L.P.
Lavarias Arnel C.
Nguyen Thong
Nlight Photonics Corporation
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