The impact of Rayleigh backscatter induced noise on QPSK transmission with Fabry-Perot lasers

The use of uncooled Fabry-Perot (FP) lasers for upstream data in cable television (CATV) networks has recently been proposed. The merits of this choice, from use in telecommunications networks, include low cost and proven reliability. Indeed, it has been shown that these devices can transmit multiple quadrature phase shift keying (QPSK) signals in an error-free manner. However, there is a bit-error-rate (BER) penalty associated with these lasers, that impacts the useable error free range. We show this degradation is caused by laser sporadic noise generated by Rayleigh backscatter into the laser from the fiber plant. In addition, we show the noise to be impulsive and that a 14 dB CNR penalty, at 1/spl times/10/sup -8/ BER, versus theoretical performance is possible.