Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-02-22
2002-03-12
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06356369
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to cable television systems using fiber optic communications, and more specifically to cable television systems having both forward and reverse information transmission using fiber optic communications.
BACKGROUND OF THE INVENTION
Cable television systems typically include a headend section for receiving satellite signals and demodulating the signals to an intermediate frequency (IF) or baseband. The down converted signal is then modulated with radio frequency (RF) carriers and converted to an optical signal for transmission from the headend section over fiber optic cable. Optical transmitters are distributed throughout the cable system for splitting and transmitting optical signals, and optical receivers are provided at remote locations for receiving the optical signals and converting them to radio frequency (RF) signals that are further transmitted along branches of the system over coaxial cable rather than fiber optic cable. Taps are situated along the coaxial cable to tap off the cable signals to tap off downstream (also referred to as “outbound” or “forward”) signals to subscribers of the system.
Various factors influence the ability to accurately transmit and receive optical signals within a cable television system. As the length of fiber optic cable within a system increases, for example, signal losses also increase. Furthermore, temperature fluctuations, which cause variation in the optical modulation index of the optical transmitter, can result in variation of the radio frequency (RF) output level of the optical receiver. Signal distortions can be caused by non-linearities in the laser and photodiode of the optical transmitter.
Although these problems can be mitigated by employing expensive techniques, e.g., decreasing fiber lengths between optical nodes, such techniques may prohibitively increase costs to both subscribers and service providers. Thus, what is needed is a better way to provide reliable and accurate transmission of optical signals within a cable television system. Furthermore, in such an improved system, there exists an opportunity to transmit externally generated information within an improved cable television system employing a novel reverse path architecture.
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Barnhardt III Hubert J.
Couturier Shelley L.
Massaroni Kenneth M.
Pascal Leslie
Scientific-Atlanta, Inc.
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