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Abstract

Light wave communication over optical fiber networks for the distribution of broadband, multiple channel CATV (Cable Televison) signals uses fibers which carry amplitude modulated broadband signals over a considerable distance (6-30 km) to a fiber node. Electrical to optical transmitters at the head end and optical to electrical receivers at the fiber node launch and receive the optical signals corresponding to the broadband CATV electrical signals. Distribution from the fiber node to subscribers is obtained by transmitting the electrical signals from the receivers at the node through a limited cascade of amplifiers along an electrical transmission line (coax cable). The limited cascade is much shorter than the fiber span and includes trunk amplifiers which are insufficient in number to add significant losses or distortion. Line extender amplifiers may be connected to output couplers located off the subscribers premises and then via electrical cables to the subscribers. In order to reduce distortion (second order distortion) which may be due to nonlinearities and interactions of signals in the transmitter, fiber and receiver, all or a portion of the spectrum which contains the lower channels is translated (block converted) to a frequency range which covers less than an octave. The converted signal is applied as an RF modulating signal to the transmitter which may contain a laser diode, and provides an amplitude modulated output. The signals are received at the output end of the fibers (at the fiber node), retranslated to the original band and filtered so that second order distortion components are removed. The broadband CATV signal is then distributed to the subscribers. Only those channels which extend over more than an octave need be combined, translated to a band which does not extend more than an octave and then transmitted as an amplitude modulated optical signal over a fiber. One or more additional fibers are used for the channels in the upper portion of the band which is not converted. The optical signals from the fibers are received, the converted portion is retranslated back to its original frequency range and combined with the other band limited portions to provide a broadband signal for distribution to the subscribers.

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First Claim