Impact of Fiber Transport on Phase Noise in mmWave Band and Beyond

This work investigates various noise sources that affect the phase noise of the radio frequency (RF) transported over an analog fiber link for microwave, mmWave bands, and beyond. Phase noise power spectral density (PSD) of the RF transported through the fiber is compared with that of the RF source for the cases with and without optical amplifiers. We study phase noise degradation as a function of length and laser linewidth (LW) through simulations for a wide range of RF frequencies. Experiments are conducted to analyze the phase noise of the optically transported RF at 5 GHz and mmWave 5G band for different LWs and RF power levels to assess their impact on phase noise and to corroborate the theoretical findings. This work will serve as a general design guideline for future 6G and radar systems that would rely on radio over fiber (RoF) for transport and optical beamforming.