Experiment of 2\(\times \)40Gbd PAM8 MISO-FSO system reinforced by high-speed optical signal coupling and precoder-shaped multi-level polar codes

This paper proposes and successfully demonstrates a high-speed optical signal coupling (HS-OSC) of 2x40Gbaud PAM8 with precoder-shaped multi-level polar codes (PS-MLPC) in a gain-oriented multiple-input single-output free space optical (MISO-FSO) system. With the pilot-based correction (PBC), the system gets a multi-path error (MPE) detecting and correcting module, which can minimize the MPE and achieve the gain-oriented HS-OSC. On the other hand, PS-MLPC is deployed in the MISO-FSO system to provide the non-uniform PAM-8 symbols and save the power budget. In the experiment, the PBC module is proven to ensure the HS-OSC process by comparing the captured waveforms. Results in the static FSO channel validate that the bit error rate (BER) of the MISO-FSO system is improved from \(4.76\times 10^{-3}\) $4.76\times {10}^{-3}$ to below \(10^{-5}\) ${10}^{-5}$ and the PS-MLPC PAM-8 saves most 0.85 dB effective signal-to-noise ratio (ESNR). Under turbulent conditions, the gain-oriented MISO-FSO system not only enhances the mean ESNR of about 4.3–5.4 dB but also mitigates the standard deviation of ESNR by 40.6–61.4 %, on which the PS-MLPC provides a Q-factor gain of 1.17–1.64 dB.