Noise Analysis for Coherent Phase-Modulated RF Fiber-Optic Link

The advantages of optical fiber as a transmission medium for microwave signals have led to an increasing interest in the implementation of RF/photonic links in radar frontends. Such applications often require a large dynamic range that is beyond the reach of conventional intensity modulation-direct detection (IM-DD) fiber-optic links. For a solution, a coherent fiber-optic link employing an optical phase-locked loop (OPLL) demodulation has been proposed promising enhanced spurious-free dynamic range (SFDR) performance. Under the ideal condition, the link should be shot-noise limited. However, the phase modulated (PM) link was shown to be penalized by the presence of other noise sources and environmental perturbations. In this work, we present a detailed analysis of the phase modulated link's different noise sources, their impact to dynamic range performance, and ways of mitigation.