Approaching coherent performance in differential detection via diversity

Digital self-coherent detection (DSCD) can be employed to approach coherent performance in optical receivers by digitally reconstructing the samples of the electrical field without employing a local oscillator. One major deficiency of this scheme is the abrupt loss of field reconstruction, and consequently phase tracking, immediately following the occurrence of a low intensity sample. A cross-polarization DSCD scheme is introduced to mitigate this problem via diversity. The proposed scheme, termed X-DSCD, provides significantly improved signal reconstruction capabilities while doubling the achievable communication rate as compared to the original single-polarization DSCD scheme: two different and independent symbol streams are transmitted via two linear polarizations. X-DSCD performance is analyzed for the case of two cross-polarized, Gaussian signals. The analysis is supported by simulation results. Introducing coding into the system, the error performance attained by X-DSCD is shown to potentially approach that of a coherent receiver.