Theory of polarization spreading techniques. I

Presents an analysis of a series of techniques grouped under the denomination "polarization spreading", the intent of which is that of making the performance of a coherent optical receiver insensitive to the polarization transformations occurring along the optical fiber, without resorting to polarization compensation or control. The principle on which Polarization spreading operates is that of spreading the signal power over different states of polarization, so that heterodyning of at least half of the optical incident bit energy is always ensured. The main results obtained concern a condition that guarantees the maximum heterodyned signal energy, some classes of spreading waveforms satisfying the above condition, the derivation of the structure and the performance of optimum receivers in Gaussian noise. The results encompass most of the binary optical coherent modulation schemes proposed and experimented, such as ASK, FSK and DPSK.>