Measurement of excess sensitivity penalty of a four-diode polarisation diversity coherent receiver

A novel optical polarisation-diversity coherent receiver is described and demonstrated. The receiver optical hybrid consists of three polarising beam splitters and four pin diodes, interconnected with polarisation maintaining fibres. Measurements over arbitrary input polarisations show a receiver sensitivity of -63±0.5 dBm for BER of 10^-9 in a 40 Mbit/s DPSK self-heterodyne system. This receiver sensitivity is within 1±0.5 dB of the sensitivity of a single-channel receiver with matched signal and local oscillator polarisation