Subcarrier multiplexing for fiber-based video distribution: A performance study.

Abstract

Subcarrier transmission of muti-channel video signals over optical fibers may find widespread application in video distribution systems. This thesis details a comparative study that has been conducted for subcarrier multiplexing systems using various video signal modulation formats. In particular, we have investigated: AM-VSB (NTSC), high-index FM, 4-level QAM, and HDTV (Zenith). For each modulation scheme, a minimum CNR must be achieved to meet the required SNR. For analog fiber optic systems, system degradation results from laser intrinsic nonlinearities and clipping at threshold, and from noise sources (laser RIN (relative intensity noise), signal shot noise and preamplifier thermal noise at the receiver). We have also considered the possibility of using laser optical amplifiers to increase the system margin. Again, device nonlinearities must be considered, as well as further degradation from signal-spontaneous beat noise. A communication system simulator software package BOSS (Block Oriented Systems Simulator) was used to develop a laser model based on the classic laser rate equations to predict nonlinear distortion. Adding Langevin noise terms to the rate equations, BOSS was also used to obtain the RIN spectrum. A similar model was developed for the optical amplifier based on the rate equation and wave equation of the optical amplifier. Results of the comparative study are given.