Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-06-18
2001-05-01
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06226112
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a high-speed commmunication system and, more particularly, to an optical time-division-multiplex system.
In recent years, as the demand for higher-capacity communication systems has proliferated, the use of optical fibers as the transmission medium in such systems has significantly increased. The attractiveness of such a medium is based on the recognition that the bandwidth of a single-mode optical fiber channel is in the teraHertz range (10
12
signals per second).
In a typical system in which an optical fiber is employed to interconnect electronic circuitry in a transmitter to electronic circuitry in a receiver, the electronic circuitry as heretofore realized is usually not capable of operating at speeds in the teraHertz range. Thus, for example, by way of an example, for a fiber carrying signals at a one-teraHertz rate, the electronic circuitry associated therewith is capable in practice of operating at only at best a 125-gigaHertz rate.
Accordingly, various multiplexing techniques (at the transmitter) and demultiplexing techniques (at the receiver) have been proposed to interface relatively low-speed electronic circuitry to high-speed fibers. In, for example, a so-called time-division-multiplex (TDM) system, multiple low-speed signal sequences at the same rate are interleaved and applied to a fiber as a single high-speed serial sequence. Thus, illustratively, by interleaving eight 125-gigaHertz signal sequences, it is feasible to utilize a one-teraHertz fiber with electronic circuitry at the transmitter and receiver capable of operating at only 125 gigaHertz. In such a system, individual signals from eight different channels are transmitted in sequence in an alternating fashion.
Heretofore, the problem of demultiplexing or distributing the interleaved optical signals propagated in a high-speed fiber in a TDM system has proven to be a formidable one. Electro-optic deflectors, for example, have been suggested for use at the receiver of a TDM system for deflecting and thereby routing successive received signals to respectively different photodetectors. But achieving electro-optic deflection in the teraHertz range is an extremely difficult, if not currently impossible, task. Also, the materials utilized in practice to realize electro-optic deflectors are typically different than the silicon-based materials commonly employed to make photodetectors and other standard components of the receiving circuitry. As a result, integrating such deflectors with the other circuitry on a single receiver chip is not easily realized using conventional batch-fabrication integrated-circuit processing techniques.
Still other approaches have been suggested for demultiplexing a stream of high-speed optical signals in a TDM system. (A review of various TDM techniques is contained in an article entitled “All-Optical Network Consortium-Ultrafast TDM Networks” by R. A. Barry et al,
IEEE Journal on Selected Areas in Communications,
vol. 14, No. 5, June 1996, pages 1000-1013.)
But these other known proposed solutions also are characterized by serious drawbacks such as extreme complexity, speed-limited capability (relative to the one teraHertz range) or lack of integratability on a single receiver chip.
Accordingly, continuing efforts have been directed by workers skilled in the art aimed at trying to provide an improved way of demultiplexing a high-speed optical signal sequence in a TDM system. It was recognized that such efforts, if successful, could provide a basis for enhancing the operation and lowering the cost of high-speed optical communication systems.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a relatively high-repetition-rate optical signal sequence in a TDM system is applied to the input end of an elongated optical waveguide that comprises along its length multiple electrically isolated two-photon photodetectors. A relatively low-repetition-rate optical probe pulse is applied to the output end of the waveguide. The timing relationship between the incoming signals and the counter-propagating probe pulse is controlled such that overlap of the probe pulse with each successive one of each set of incoming signals occurs in respectfully different photodetectors in the waveguide. For each such overlap, two-photon non-linear absorption of the propagating radiation occurs in a different photodetector and an electrical output signal therefrom is thereby provided. Neither the optical probe pulse nor the optical signal by itself is sufficient to produce a usefully distinguishable electrical output signal from a photodetector in which non-overlapping optical radiation occurs.
REFERENCES:
patent: 4883334 (1989-11-01), Chiarulli et al.
patent: 5172258 (1992-12-01), Verber
patent: 5654812 (1997-08-01), Suzuki
R.A. Barry et al, “All-Optical Network Consortium-Ultrafast TDM Networks”,Jun. 1996, pp. 999-1013,IEEE Journal on Selected Areas in Communications, vol. 14, No. 5.
Denk Winfried
Lenz Gadi
Shmulovich Joseph
Xu Chunhui
Agere Systems Inc.
Chan Jason
Leung Christina Y
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