From Event: International Conference on Space Optics — ICSO 2021, 2021
Compensating atmospheric turbulence is of paramount importance to deploy high-speed laser communication links. Beside classical adaptive optics compensation scheme, spatial division multiplexing approach based on Multi-Plane Light Conversion (MPLC) proves to be an efficient, scalable, and easy to implement solution to mitigate turbulence [3]. The principle is to collect spatial modes of the complex field like Hermite-Gaussian modes (as opposed to modes of the phase, like Zernike) into a multimode input - fibered or in free space - and selectively demultiplex them with an MPLC into single-mode fiber (SMF) outputs.
Former experiments have shown that this technique offers a net coupling gain and enhanced stability of the signal in presence of atmospheric turbulence. However, due to the multiple SMF outputs, performing a telecommunication link requires complex numerical post-processing to rephase the signals from SMFs.
To overcome this issue, we developed an all-optical coherent recombiner. We designed and fabricated an 8 to 1 all-optical coherent recombiner matching turbulence mitigation requirements. 8 SMF inputs with polarization maintaining (PM-SMF) are combined in a cascaded manner into a unique PM-SMF output. Using Mach-Zehnder interferometers, we can balance the different inputs in amplitude and phase lock the different channels. To provide a low-cost component compatible with industrials requirements, we favored intensity monitoring of the leaks with photodiodes to control the feedback loop. The recombiner is designed to operate at a speed >1 kHz enabling high-speed atmospheric turbulence compensation independently of the throughput. We tested the turbulence mitigation module based on an MPLC followed by this recombiner on an atmospheric turbulence emulator optical bench.
In this work, we present the atmospheric turbulence mitigation module based on an MPLC and an all-optical recombiner. We demonstrate significant gain when coupling a perturbated signal into a unique single-mode fiber with a turbulence emulation bench at a data rate of 1 Gb/s.
© (11 June 2021) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David Allioux, "Turbulence mitigated single-mode fiber output based on Multi-Plane Light Conversion technology with all-optical coherent recombiner," Proc. SPIE 11852, International Conference on Space Optics — ICSO 2020, 118525X (Presented at International Conference on Space Optics — ICSO 2021: 11 June 2021; Published: 11 June 2021); https://doi.org/10.1117/12.2600025.