Evaluation of a multimode receiver with a photonic integrated combiner for satellite to ground optical communications

Multimode receivers based on spatial or modal diversity are promising architectures to mitigate in real time the atmospheric turbulence effects for free space optical (FSO) communications. In this paper, we evaluate and comment on the dynamical communication performances of a FSO mode diversity receiver, based on a spatial demultiplexer and a silicon photonic coherent combiner, for an optical link from a GEO satellite to an optical ground station (OGS). We simulate time series of distorted wavefronts received by the OGS and we show numerically that the coherent combination of spatial modes mitigate the signal fading compared to a conventional single mode fiber (SMF) receiver. We verify this property in a laboratory environment by generating the wavefronts corresponding to the use case with an atmospheric propagation channel emulator. Then we modulate the optical carrier prior to the wavefront emulator with 10G OOK and DPSK data sequences to measure the BER performance of the proposed receiver during the time series emulation. Finally, we study and comment on the influence of the number of modes combined and the wavelength multiplexing on the BER performances. We prove that the mode diversity receiver provide a higher collection efficiency, has better BER performances and much less synchronization losses.