Coherent optics enabling fading resilient free space transmission

We review time-diversity techniques to help data from free-space optical systems survive power drops caused by atmospheric turbulence. We report on one successful implementation using two WDM time-delayed commercial transponders at 100Gb/s and FPGA extenders. We investigate possible enhancements of these techniques in the lab and propose a method to make transponders more robust to turbulence by freezing all Digital Signal Processing (DSP) iterative operations during power fading events. We demonstrate it over a real-time receiver prototype, achieving a tolerance to signal interruptions increased by a factor of 500 compared to conventional coherent DSP architectures.