A GENERALIZED SUBOPTIMUM UNEQUALLY SPACED CHANNEL ALLOCATION TECHNIQUE - PART II - IN COHERENT WDM SYSTEMS

Four-wave mixing (FWM) in dispersion-shifted optical fiber is a major problem associated with low optical input power levels in optical wave length-division multiplexed (WDM) systems, To reduce the crosstalk cau sed by FWM, a generalized suboptimum unequally spaced channel allocati on (S-USCA) technique has been proposed in [1], While the S-USCA techn ique reduces FWM power substantially, it also reduces the minimum chan nel spacing compared to conventional equal channel spacing (ECS) syste ms when the same number of carrier channels are accommodated in a fixe d optical bandwidth. This results in more interchannel interference (I CI) when employing the S-USCA scheme. The power penalty of the ECS and the S-USCA systems caused by crosstalk and frequency drift are invest igated and compared in this paper. The superior system performance reg ion, where S-USCA systems out perform ECS systems, is also quantified, For 20-channel systems using amplitude-shift keying (ASK) heterodyne detection scheme, for instance, results show that the S-USCA technique pays less power penalty up to bit rates of 5.5, 7.5, and 9.5 Gb/s, wh en all channels have identical states of polarization and the launched input power per channel P-in equals to -6, -3, and 0 dBm, respectivel y.