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.
