Performance analysis of direct detection optical FSK in the presence of fibre chromatic dispersion

Abstract

A novel theoretical analysis is provided for direct detection optical FSK transmission system with Mach-Zender interferometer (MZI) as an optical frequency discriminator (OFD). The analysis is carried out taking into account the combined effect of laser phase noise, chromatic dispersion of optical fibre, photodetector shot noise and receiver noise. The single mode fibre is modeled as a bandpass filter with flat amplitude response and linear !,'fOUP delay over the optical ban9width of the modulated optical signal. The statistics of the signal phase fluctuations at the output of the fibre caused by non-linear filtering due to fibre chromatic dispersion are determined in tenns of its moments and the probability density function (pdf) of the random phase fluctuation due to laser phase noise and fibre chromatic dispersion is evaluated. The total phase noise power at the output of the receiver photodetector is also expressed in terms of the powers of the crossm? dulation and intermodulation frequency noise components. Using the noise statistics and moments, the bit error rate (HER) performance of the receiver is then evaluated for different values of dispersion coefficient and laser Iinewidth at a bit rate of 10 Gbit/s. The penalty suffered by the system due to dispersion and phase noise is then determined at a bit error rate (BER) of 10.9 For a specified power penalty of I dB, the maximum allowable fibre lengths are then determined for different values of the fibre dispersion coefficient and normalized laser linewidth.