Simulation of M-QAM compressed digital video signals transmission for CATV distribution networks using semiconductor optical amplifier as an external modulator

Proposes an optical CATV digital link that transmits hundreds of M-QAM compressed digital video signals by using a traveling wave semiconductor optical amplifier (TWSOA) as an external modulator and a high-power DFB laser as the CW source for the external modulator, as another alternative to directly modulated DFB laser based transmitters. Semiconductor optical amplifiers have long been considered not suitable for CATV systems which transmit multi-channel AM-VSB video signals, due to the carrier-density-modulation induced second order nonlinear distortions (NLDs). However, despite the fact that these second-order NLD levels cannot be tolerated by AM-VSB signals, they may be acceptable to subcarrier-multiplexed digital video channels using M-QAM format. We use computer simulation techniques to investigate the potential and limitations of TWSOAs when used as external modulators at the transmitter end of multi-channel M-QAM CATV lightwave systems. We have numerically shown that by using 16/64-QAM and a TWSOA as an external modulator, one could transmit up to 400/600 MPEG2 video channels with an optical CATV digital link budget of 34/27 dB