Performance Evaluation of Digital Coherent Receivers for Phase-Modulated Radio-Over-Fiber Links
ABSTRACT The performance of optical phase-modulated (PM) radio-over-fiber (RoF) links assisted with coherent detection and digital signal processing (PM-Coh) is analyzed and experimentally demonstrated for next-generation wireless-over-fiber systems. PM-Coh offers high linearity for transparent transport of high-frequency microwave signals, and better receiver sensitivity than intensity modulated with direct detection systems. By including photonic downconversion in the PM-Coh link, in a form of a pulsed free-running local oscillator, it is possible to receive high-RF carrier frequencies, with low-bandwidth electronics. Analytical assessment and simulations are used to determine the ultimate performance with respect to laser linewidth, modulation index, and receiver sensitivity. Then, two different scenarios are studied and experimentally demonstrated as an application of PM-Coh links: a high-capacity multiantenna RoF system (12 subcarriers of 400 Mb/s and 6 subcarriers of 800 Mb/s) and photonic downconversion for the detection of high-RF carriers microwave signals (up to 3.2 Gb/s at 40 GHz).