Saturation in wavelength-division multiplexing free-space optical communication systems

Non-Adaptive Decision Thresholds for Gain Saturated FSO Links Limited by Weak to Strong Turbulence and Pointing Errors

“…Also h P P av in = where nt tx av L P P = represents the turbulence-free average power at the input of the OA where nt L is the turbulence-free fixed path loss. The ability of an OA operated in the saturation regime to mitigate scintillation and achieve BER performances below the forward error correction (FEC) limit in the weak turbulence regime when a non-adaptive decision threshold is used at the receiver has been shown in [23,24]. This is so because in a turbulent atmosphere where the instantaneous powers at the OA input follows the respective (depending on the turbulence strength) turbulence distribution PDF, powers high enough to drive the OA into saturation and low powers reduces and increases the OA gain respectively.…”

“…Optical amplifiers (OAs) have been shown to improve receiver sensitivity in FSO communication systems [20] and the impact of amplified spontaneous emission (ASE) beat noises such as signal-spontaneous and spontaneous-spontaneous beat noises on system performance have been studied [5]. Gain saturation in an OA has been experimentally [21] and theoretically [22,23] shown to mitigate scintillation effects (with acceptable BER results in the weak turbulence regime [23,24]) since saturation allows for gain adjustment in the OA based on the turbulence-induced varying power levels. It is also shown in [23] that the benefits of gain saturation in a pre-amplified FSO communication system limited by a turbulent atmosphere is primarily evident when a nonadaptive threshold is used at the receiver, otherwise, gain saturation (reduced gain) will only reduce system performance.…”