High performance packaged optical coherent hybrid

The fabrication and characterisation of a compact packaged optical hybrid at lambda =1.3 mu m is described. The hybrid design offers low excess loss (less than 0.7 dB), high polarisation cross-talk ratio (greater than 32 dB) and long term performance stability. Proper function of several hybrids has been demonstrated in a 1.7 Gbit/s FSK polarisation diversity field experiment for over a month. Optical power, P_in, for a 10^-9 bit error rate was measured at -40 dBm, with less than 0.6 dB variation due to polarisation fluctuation. Long term error free operation with less than one error a day was achieved at -36 dBm.