Polarisation insensitive coherent transmission by synchronous intrabit polarisation spreading

Polarisation independent heterodyne detection of an FSK signal has been demonstrated by the synchronous intrabit polarisation spreading technique, i.e. by applying a proper periodical modulation at the clock frequency to the state of polarisation of the laser output field. A 155 Mbit/s FSK transmission experiment at 1.55 mu m has shown an excess penalty within 1.5 dB of the expected performance of the ideal polarisation diversity transmission.