Improving Free-Space Optical Communication with Adaptive Optics for Higher Order Modulation

One of the biggest challenges of free-space optical (FSO) communication is the wave-front aberration due to atmospheric turbulence. In FSO links the wave-front distortion manifests as a significant drop in received power, beam wander, information loss, and scintillation effects. The performance of FSO communication system is degraded significantly by the atmospheric turbulence effects. Fortunately, the adaptive optics system offers potential to mitigate the performance degradation, which is relevant for quantum communication applications as well. In our FSO experiment, we perform the transmission of 6.25 GBd QPSK signal over an FSO link without and with adaptive optics, operating at 1550nm. We emulate the atmospheric aberration in our indoor experimental setup by applying random Kolmogorov phase screens on spatial light modulators (SLMs). We demonstrate significant improvements in the power-collected, signal-to-noise-ratio (SNR), and bit-error-rate (BER) performance due to the application of adaptive optics.