Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
2001-11-16
2004-05-04
Cherry, Euncha (Department: 2872)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S008000, C372S023000, C372S050121
Reexamination Certificate
active
06731850
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a photodetector and more particularly to a photodetector having spatially varying wavelength absorption properties within a single semiconductor structure. The present invention is further directed to a method of making such a photodetector.
DESCRIPTION OF RELATED ART
High-speed networking is required both in local areas and at points of access to high-speed metropolitan-area networks. Active optical components are needed to detect optical signals on many wavelengths in a cost-effective manner. A very broad bandwidth needs to be addressed to take full advantage of emerging optical fiber technologies with low loss from 1300 to 1600 nm and beyond.
Traditional techniques for wavelength-division demultiplexing have used some sort of refracting or diffracting optical element to break up incoming signals by wavelength to apply the various wavelengths to multiple photodetectors. However, such techniques have resulted in devices which are expensive to manufacture.
U.S. patent application Ser. No. 09/833,078 to Thompson et al, filed Apr. 12, 2001, entitled “A method for locally modifying the effective bandgap energy in indium gallium arsenide phosphide (InGaAsP) quantum well structures,” and published Mar. 14, 2002, as U.S. Ser. No. 2002/0030185 A1, whose entire disclosure is hereby incorporated by reference into the present disclosure, teaches a method for locally modifying the effective bandgap energy of indium gallium arsenide phosphide (InGaAsP) quantum well structures. That method allows the integration of multiple optoelectronic devices within a single structure, each comprising a quantum well structure.
In one embodiment, as shown in
FIG. 1A
, an InGaAsP multiple quantum well structure
104
formed on a substrate
102
is overlaid by an InP (indium phosphide) defect layer
106
having point defects
108
, which are donor-like phosphorus antisites or acceptor-like indium vacancies. Rapid thermal annealing (RTA) is carried out under a flowing nitrogen ambient, using a halogen lamp rapid thermal annealing system. During the rapid thermal annealing, the point defects
108
in the defect layer
106
diffuse into the active region of the quantum well structure
104
and modify its composite structure. The controlled inter-diffusion process causes a large increase in the bandgap energy of the quantum well active region, called a wavelength blue shift.
Another embodiment, as shown in
FIG. 1B
, uses two defect types, one to generate a wavelength blue shift and the other to decrease carrier lifetime. A first InP defect layer
110
contains slowly diffusing vacancy defects
114
, while a second InP defect layer
112
includes rapidly diffusing group V interstitial defects
116
. Rapid thermal annealing causes both types of defects to diffuse into the quantum well active region.
However, the above-noted problem of the demultiplexing photodetector has not yet been solved.
SUMMARY OF THE INVENTION
It will be readily apparent from the above that a need exists in the art for a compact, inexpensive demultiplexing photodetector. It is therefore an object of the present invention to provide a demultiplexing photodetector in a single semiconductor structure. It is another object of the invention to provide an inexpensive manufacturing technique for such a photodetector.
To achieve the above and other objects, the present invention is directed to a photodetector in which multiple wavelength detecting regions are integrated into a monolithic semiconductor structure, as well as to a method of making such a photodetector using the technique described above or any other suitable intermixing technique. The photodetector uses the above-described techniques to provide multiple photodetecting regions and thus to provide an integrated serial single-waveguide ultra-broadband photodetector. The invention exploits the above-described technique to shift the absorption edge locally. A waveguide is used to carry the light along the length of the device. All materials can be grown semi-insulating and on a semi-insulating substrate to achieve electrical isolation between different wavelength-detecting regions. The length of the device and thus the bandgap grading length achieved by intermixing are chosen so that all high-energy photons are absorbed in the early absorption regions. Wavelength-resolving capability then given approximately by:
grading rate (&mgr;m per &mgr;m)/(loss in microns).
For 2000 cm
−1
, hence 0.2 &mgr;m
−1
, a spatial grading rate of 10
−4
&mgr;m/&mgr;m would give a resolution of about 5×10
−4
&mgr;m, or about 0.5 nm. This device could demultiplex and detect the entire spectrum 1.3-1.6 &mgr;m (hence 0.3 &mgr;m of bandwidth) in a device length of 600 &mgr;m, hence less than 1 mm. Achieving this resolution will depend on the sharpness of the local spectra of the photoconductive materials and on the sophistication of electronic signal-processing capabilities. Nonlinearity in grading or other properties may be precisely compensated using reciprocally nonlinear variable contact spacing.
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Blank Rome LLP
Cherry Euncha
Fox-Tek
LandOfFree
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