Performance and limits of a Kramers-Kronig self-coherent receiver in a turbulent 800 m free-space optical link

Free-space optical communications systems offer increased data rates and improved channel security in comparison to conventional radio frequency systems for wireless communications. By using the coherent properties of laser light, coherent communication systems have arisen in laser links as a means to increase the data rates. One method of coherent communication is based on the Kramers-Kronig coherent receiver which can retrieve phase information from intensity-only measurements using digital signal processing. As atmospheric turbulence in the optical path will degrade the signal quality in a free-space optical link, the Kramers-Kronig method was tested in an outdoor free-space optical path with data rates on the order of Gbit/s. This free-space optical link was used to record simultaneously the laser spot on a camera, the bit error rate of the received signal, and the average optical power hitting the photodetector after propagation through turbulence. All three measurements were synchronized in an attempt to correlate the effect of atmospheric turbulence on the Kramers-Kronig coherent receiver method.