High-Fidelity Long-Haul Microwave Photonic Links with Composite OPLLs and Multi-Core Fiber for Secure Command and Control Systems in Contested Environments

Secure communication for critical command nodes has emerged as a pivotal challenge in modern warfare, in particular considering the vulnerability of these nodes to electronic reconnaissance. To cope with the severe interference, this paper proposes a robust solution for long-distance secure command and control system leveraging phase-modulated microwave photonic links. Studies that analyze the impairing nonlinear distortions and phase noise stemming from different sources in optical phase demodulation during long-haul transmission has been carried out, unveiling their impairment in coherent transmission systems. To overcome these limitations, a linearized phase demodulation and noise suppression technique based on composite optical phase-locked loop and multi-core fiber is proposed and experimentally validated. Experimental results demonstrate a long-haul transmission over 100 km with an 81 dB suppression for third-order intermodulation distortion and a 27 dB improvement in noise floor at 5 MHz under closed-loop condition, verifying a significant enhancement in the fidelity in long-distance transmission. This method ensures a highly reliable secure communication for command and control systems in contested electromagnetic environments.