Radio-Over-FSO/Fiber Systems for 5G Sub-6 GHz/MMW Signal Transmission Using Broadband MZM and TOBPF

The implementation of radio-over-free-space optical (FSO)/fiber systems with broadband Mach-Zehnder modulator (MZM) and tunable optical band-pass filter (TOBPF) is successfully realized. By employing a broadband MZM at the transmission side, fifth generation (5G) sub-6 GHz and millimeter-wave (MMW) signals will be modulated and transmitted. By employing a TOBPF at the receiving side, one can capture a desired optical sideband along with a portion of the central optical carrier, enabling direct detection of the modulation signal using a low-bandwidth PD. This approach mitigates fiber dispersion-induced RF fading and eliminates the need for high-frequency RF components. Over 10 m (sub-6 GHz)/20 m (MMW) 5G wireless, 1.6 km FSO, and 40 km single-mode fiber hybrid-media, 1 Gbps at 4.7 GHz, 10 Gbps at 28 GHz, and 20 Gbps at 60 GHz 16-quadrature amplitude modulation-orthogonal frequency-division multiplexing signals are delivered with impressive performance of low bit error rates and error vector magnitudes, and clear constellations. The successful transmission of 5G sub-6 GHz/MMW signal over radio-over-FSO/fiber systems shows its potential to meet the demands of future systems, especially for high adaptability to different frequency bands.