Simultaneous Implementation of All-Optical Microwave Bandpass Filtering and Up-Conversion for Radio-Over-Fiber Applications

Based on single-sideband (SSB) modulation, a novel scheme to simultaneously implement all-optical microwave bandpass filtering and up-conversion is proposed, which is favorable for radio-over-fiber (ROF) applications. SSB modulation with different sidebands will theoretically bring $\pi$ phase difference on a microwave signal by utilizing dual-electrode Mach–Zehnder modulators. This effect is the key to the realization of bandpass filtering, which was experimentally verified. With the help of several other photonic devices, a five-tap bandpass filter integrated with heterodyne-detection-based microwave frequency up-conversion was demonstrated theoretically. Besides the up-conversion function, the simulation certification of our proposed scheme also indicated some well filtering characteristics, such as more than 2-dB secondary sidelobe ratio improvement, the reconfigurability by applying different window functions, the filtering tunability with the center intermediate frequency (IF) from 2.16 to 4.08 GHz, and the moderate tolerance to a large dynamic IF input signal. The proposed scheme features the feasibility of the integration of some cost-effective frequency multiplication methods and the flexible bandpass-filtering characteristics for millimeter-wave ROF systems.