Optical satellite uplinks rely on high-power optical amplifiers (HPOAs) to overcome free-space attenuation and enable long-distance transmission. However, at high power levels, fiber Kerr nonlinearity becomes significant and degrades system performance. In this work, we develop a realistic model for optical uplinks that accounts for nonlinear effects and analyze their impact, highlighting key differences from conventional longhaul fiber systems. We then introduce low-complexity digital signal processing techniques for nonlinearity compensation, based on constellation shaping via a look-up table (LUT) and a simple nonlinear phase rotation applied at the transmitter and/or receiver. The LUT also enables adaptive rate tuning according to channel conditions, enhancing robustness against link variations. Simulation results show that the proposed techniques increase the maximum acceptable link loss by up to 6 dB with negligible complexity. Finally, we show that, at the system level, propagation in the HPOA can be modeled as a simple nonlinear phase rotation, equivalent to propagation in a zero-dispersion noiseless fiber link, and fully characterized by a single parameter - the characteristic nonlinear power.

翻译：光卫星上行链路依赖高功率光放大器以克服自由空间衰减并实现长距离传输。然而在高功率条件下，光纤克尔非线性效应变得显著并会降低系统性能。本研究建立了考虑非线性效应的光上行链路实际模型，分析了其影响，并强调了其与传统长途光纤系统的关键差异。随后，我们提出了基于查找表星座成形及在发射端和/或接收端施加简单非线性相位旋转的低复杂度数字信号处理非线性补偿技术。该查找表还能根据信道条件实现自适应速率调节，增强了对链路变化的鲁棒性。仿真结果表明，所提技术可将最大可接受链路损耗提升高达6 dB，且复杂度可忽略不计。最后我们证明，在系统层面，高功率放大器中的传输可建模为简单的非线性相位旋转，等效于在零色散无噪声光纤链路中的传输，且仅需单一参数——特征非线性功率即可完全表征。