Low-complexity turbulence resilience enabled by a multi-mode bi-directional transceiver

Free-space optical (FSO) communication systems are acutely affected by the pointing issues and distortions that result from mechanical instability and environmental factors such as turbulence. These distortions have generally prevented single-mode bi-directional systems from being deployed without adaptive optics due to high optical losses. We investigate and compare the performance of both step and graded index multi-mode fibers for bi-directional communications over an emulated 400 m FSO channel. We propose that OM5 graded index fiber will simultaneously provide a near Gaussian optical transmission mode and a factor of greater than 5 increase in the field of view compared to single-mode fiber. We demonstrate that OM5 can support an error-free throughput of 10 Gbps for low-turbulence (D/r₀ = 3) and 9.1 Gbps for high-turbulence (D/r₀ = 9) using commercial bi-directional small form-factor pluggable (SFP+) transceivers with no adaptive optical components.