Extinction ratio effect for high-speed optical fiber transmissions

In conventional optical transmissions, the extinction ratio is expected to be as high as possible in order to get better receiver sensitivity. But for high-speed long distance optical transmissions, the system performance is mainly dependent on the self-phase modulation (SPM) when the input optical power is sufficiently high. It is possible that a large improvement of the receiver sensitivity can be obtained by using an input signal with finite extinction ratio when the SPM takes effect. In this paper, the interaction of the fiber dispersion, SPM, prechirp and extinction ratio is investigated and the optimisation of system performance is implemented for a 10 Gbit/s long distance unrepeatered unregenerate optical transmissions.