Numerical simulation studies of the effects of noise and optical-fiber distortion on wideband frequency-modulated cable television systems.

摘要

Wideband frequency modulation (WFM) can improve the sensitivity of the CATV fiber system by exploiting the large bandwidth available in an optical fiber. This work examines the fundamental limiting factors in a WFM fiber optic system and calculates their quantitative effects for a general WFM CATV system. The specific design example of a high-performance 80-channel WFM CATV supertrunking system is also examined.; Numerical simulation is used to study the effects of fiber dispersion and other system effects on the WFM system. In particular, fiber dispersion is shown to degrade the carrier-to-noise ratio (CNR) of the CATV channels by an effect we call dispersion-induced power loss. Thus, CNR becomes the fiber dispersion-limiting factor, rather than composite-second-order (CSO) and composite-triple-beat (CTB) distortions.; The effects of finite photoreceiver bandwidth are shown not to be a limiting design factor.; Analytical calculations of FM modulator phase noise and double Rayleigh backscattering are performed. Examination of the minimum noise performance required in a WFM system shows that an opto-electronic modulator is not suitable for a high-performance 80-channel WFM system. This result was not expected since previous work indicates that an opto-electronic FM modulator is favored. However, that work is based on more relaxed CNR requirements and fewer channels.; Finally, the contributions of double Rayleigh back-scattering noise and discrete reflection noise are calculated and shown not to be a limiting factor. This result provides a mathematical explanation of other experimental results. (Abstract shortened by UMI.)