Experimental demonstration of enhanced coherent free-space optical communications with optical frequency comb in atmospheric turbulence

In this paper, an optical frequency comb (OFC) based wavelength division multiplexing (WDM) scheme for coherent free-space optical (FSO) communications in atmospheric turbulence was proposed. In the scheme, by exploiting the broadband phase coherence of comb lines and the correlation of phase noise for different wavelength channels, a phase noise sensing (PNS) channel was constructed to perceive the phase noise for all of the information symbols even in different wavelength channels. In other words, the estimated phase noise in PNS channel can compensate the phase noise in other wavelength channels regardless of whether the span between the PNS channel and other wavelength channel was small or big. An experiment was built to validate the scheme. The experimental results showed that great improvement of bit error rate performance can be brought by the proposed scheme, namely, the WDM based coherent FSO communications with OFC was enhanced.