Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-03-27
2001-08-07
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06271943
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical communications devices and in particular to a device for demultiplexing optical signals.
BACKGROUND OF THE INVENTION
Optical communications may soon be the standard for high-speed local area networks (LAN). Within a few years, the data rates on such networks will be about one gigabit per second (Gbit/s). As capacity requirements exceed 1 Gbit/s, it may be desirable to use wavelength division multiplexing to increase the aggregate data rate of existing fiber in such LANs.
A multiple vertical cavity surface emitting laser (VCSEL) transmitter operating at 820, 835, 850 and 865 nm has recently been proposed as a WDM source for a LAN. To demultiplex the signal, a complicated arrangement of filters packaged with waveguide splitters was used. See, Aronson et al., “Low-Cost Multimode WDM for Local Area Networks,” Postdeadline Session of the 1997 Optical Fiber Communication Conference.
It would be desirable, therefore, to have a simpler arrangement for demultiplexing such a signal to minimize the cost of such a network.
SUMMARY OF THE INVENTION
A wavelength demultiplexer having at least two pairs of “stacked” photodetectors is disclosed. The photodetectors are arranged in sequential layers along an optical path and the pairs of photodetectors are separated by a non-optically active insulator interposed between the pairs. The photodetectors differ in bandgap, and are arranged so that the optical signal passes through relatively larger bandgap photodetectors before being received by relatively smaller bandgap detectors. Each photodetector absorbs photons within a predetermined energy range and generates a voltage as a function of the absorbed energy. The photodetectors can be used to detect, and hence demultiplex, a wavelength-division-multiplexed signal.
In a preferred embodiment of the present invention, the photodetectors utilize multiple quantum well (MQW) material grown via molecular beam epitaxy. The MQW structure of the photodetectors enables the present photodetector-based demultiplexer to detect multiplexed signals that differ in wavelength by as little as 15 nanometers (nm). Conventional photodetector-based demultiplexers utilizing bulk materials cannot be used in conjunction with such close channel spacing. Typically, such conventional devices require channels separated by about 150 nm.
REFERENCES:
patent: 5627383 (1997-05-01), Cunningham
patent: 5827016 (1999-02-01), Cunningham
patent: 5949561 (1999-09-01), Gooossen
L. B. Aronson et al., “Low-Cost Multimode WDM for Local Area Networks,” Conference on Optical Fiber Communications,Technical Digest, Postconference 6:420-3 (1997).
J. C. Campbell et al., “Improved Two-Wavelength Demultiplexing InGaAsP Photodetector,”IEEE Journal of Quantum Electronics, QE-16, No. 6, pp. 601-603 (1980).
K. W. Goossen et al., “Electroabsorption in ultranarrow-barrier GaAs/AlGaAs multiple quantum well modulators,”Applied Physics Letters, 64, No. 9, pp. 1071-1073 (1994).*
Swaminathan et al., “Material Aspects of GaAs and InP Based Structures,” Crystal Growth, Ch. 2, pp. 138-155 (Prentice Hall, 1991).
Agere Systems Optoelectronics Guardian Corp.
Bello Agustin
Chan Jason
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