All-fibre optical hybrid for coherent polarisation diversity receivers

The design, fabrication and characterisation of an all polarisation maintaining fibre coherent hybrid at λ = 1.55μm utilising a polarisation splitter coupler and a 3 dB coupler tree is reported. The compact packaged coupler-based hybrid exhibits low excess insertion loss (less than 0.6 dB), wide operation-bandwidth (greater than 100 nm) and high polarisation crosstalk ratio. Stable operation of the hybrid functions has been demonstrated in a polarisation diversity configuration transmission system experiment at l.7 Gbit/s and 2.5 Gbit/s, with receiver sensitivities of −42 and −38 dBm, respectively.