SOA-Based Multilevel Polarization Shift On–Off Keying Transmission for Free-Space Optical Communication

This paper proposes a semiconductor optical amplifier (SOA)-based multilevel polarization shift on–off keying (MPS-OOK) transmission for free-space (FSO) communication. At the transmitter end, MPS-OOK signal is modulated with constant linear state of (SOP) at high-intensity level and various SOPs low-intensity in order to improve spectral efficiency (SE) transmitted power efficiency. receiver first, polarization-independent SOA was introduced optically suppress turbulence-induced scintillation effect equalize intensities deep gain saturation without distortion. Then, polarizer (LP) high extinction ratio (ER) deployed convert equalized into known intensity. Finally, converted detected using single photodiode (PD) distinguished fixed-threshold decision (M-FTD). The proposed technique evaluated experiments. A Mach–Zehnder modulator (MZM)-based fading simulator emulate effect. experimental results demonstrated that effectively mitigated SE improved by up 2 bit/s/Hz four-level (4PS-OOK) transmission.