Stokes‐parameter detection experimental results for polarization modulation coherent systems with low bit‐rate‐to‐linewidth ratio

A BER measurement has been performed relative to each Stokes parameter in an ASPSK system using laser sources such that the beating signal linewidth exceeds the bit rate (about 200%). Under such severe conditions a sensitivity of about 155 photons/bit has been achieved at a BER of 10 −9 , with a penalty of about 6 dB with respect to the quantum limit of an ASPSK system. © 1993 John Wiley & Sons, Inc.