Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2002-02-01
2004-08-03
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S038000, C385S027000, C250S208600
Reexamination Certificate
active
06771856
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to optical fiber systems and, more particularly, is related to systems and methods for detection and compensation of modal dispersion in optical waveguides.
BACKGROUND OF THE INVENTION
In an optical communication system deploying a multi-mode fiber (MMF), an optical signal launched into the fiber propagates along the fiber as multiple modes, each of which exhibits a different group velocity. A portion of the source optical signal resides in the different modes. The multiple modes can have different arrival times at the end of the fiber. The different group velocities of the modes cause a pulse formed from more than one mode to spread out as it propagates, and is referred to as intermodal dispersion which distorts the optical signal. Intermodal dispersion causes the optical signal initially launched through a fiber at a predetermined frequency and an initial phase to vary as a function of the length of the fiber.
Modal dispersion reduces the maximum data transmission rate of the optical communication system and thus diminishes the total transmission capacity of the fiber. This results from the fact that modal dispersion spreads the optical pulse as it propagates. Thus, short pulses are limited to very short transmission distances and longer pulses can be transmitted further since the relative distortion of the pulse is smaller. Since shorter pulses typically require more bandwidth, multimode fiber is characterized by a bandwidth-distance product. Importantly, the bandwidth-distance products of typical multimode fiber are severely limiting. Modem multimode fiber incorporates a graded optical index profile within the core of the fiber to reduce modal dispersion. Unfortunately, modal dispersion remains the dominant bandwidth limiting mechanism in multimode fibers. Furthermore, as compared to single mode fibers, these limits reduce the capacity of multimode fiber by orders of magnitude.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned and/or other deficiencies and/or inadequacies.
SUMMARY OF THE INVENTION
The present invention provides methods for compensating for modal dispersion in multimode optical communications systems. Briefly described, one embodiment of the invention, among others, can be implemented as follows. The method includes detecting, in a multi-mode fiber optic system having an optical signal coupled into a multi-mode fiber, a plurality of optical signals radiating from an end of the multi-mode fiber by a multisegment photodetector. Typically, the multisegment photodetector has different detector regions that detect different portions of the plurality of optical signals. The method also includes modifying the detected signals to reduce the effects of modal dispersion among the plurality of optical signals.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.
REFERENCES:
patent: 3689772 (1972-09-01), George et al.
patent: 3777150 (1973-12-01), Miller
patent: 3988614 (1976-10-01), Kapron et al.
patent: 4050782 (1977-09-01), Uchida et al.
patent: 2001/0036334 (2001-11-01), Choa
Haas, Z. and Santoro, M.: (Jul. 1993) “A Mode-Filtering Scheme for Improvement of the Bandwidth-Distance Product in Multimode Fiber Systems”,Journal of Lightwave Technology, vol. 11 (7), pp. 1125-1130.
Pending Application, Serial No.: 10/061,621; Filed Feb. 1, 2002, entitled “Segmented Photodetectors For Detection and Compensation of Modal Dispersion in Optical Waveguide”.
Shur, M.S. (1996) “MSM Photodector” drawing,Introduction to Electronic Devices, Wiley Publishing.
Patel Ketan
Ralph Stephen E.
Georgia Tech Research Corporation
Lee John D.
Pak Sung
Thomas Kayden Horstemeyer & Risley LLP
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