Adaptive optics for the free-space coherent optical communications

• Using AO-corrected focal images to simulate the performance of a homodyne receiver.
• A relation between SR, RMS, and the mixing efficiency is acquired.
• The Receiver requirements are derived from necessary D/r0 values.

We present the results that the performances of the atmospheric coherent optical communications improved by a real 127-element adaptive optics system operating in 1550 nm wavelength on a 1.8 m telescope. The mixing efficiency and the BER of the homodyne free-space optical coherent communications have been analyzed with the correction of the adaptive optics system. It is shown that, the AO can expand the scope of the atmospheric turbulence condition D/r0(1550)D/r0(1550) from 1 to around 6.5 in which the coherent optical communications can function well. In order to acquire favorable results, the mixing efficiency should be larger than 0.4 and the residual wavefront error after the AO correction should be smaller than λ/6. We also find that the mixing efficiency of the coherent homodyne receiver is approximate to the Strehl ratio of the far field of the signal light. In conclusion, we have shown that the adaptive optics is a very promising technique that can largely improve the performances of the free-space coherent optical communications degraded by the atmospheric turbulence.