Polarization-Multiplexed Optical Wireless Transmission With Coherent Detection

In this paper, we propose, analyze, and experimentally verify polarization-multiplexed optical wireless transmission with coherent detection as a means of improving performance and increasing the per-wavelength data rate in the presence of atmospheric turbulence. It is first shown that in terrestrial last-mile applications, the polarization state changes of the optical wireless signal are governed by optical source properties both in the absence and in the presence of mild to moderately severe turbulence. Under these conditions, it is shown that the polarization evolution is reduced to a polarization state rotation wherein the cross-polarization interference can be equalized with well-known blind algorithms. We also experimentally verify the analytical findings, demonstrating 112 Gb/s POLMUX-QPSK transmission with coherent detection in a non-fading free-space channel, and numerically extend the experimental results to turbulent settings by invoking the lognormal model for turbulence-induced fading. Performance gains of 5-14 dB along with a doubling of the data rate through polarization multiplexing are exhibited compared to legacy single-polarization intensity modulation/direct detection (IM/DD) optical wireless systems. The presented analytical and experimental results indicate that the proposed approach is promising for notably increasing the data rate in last-mile free-space optical transmission.