Fiber-Wireless Hybrid Systems Employing Polarization-Demultiplexed Direct Detection Technique and Keplerian Telescope With Triplet-Lens Telescope

A fiber-wireless hybrid system employing polarization-demultiplexed direct detection technique and Keplerian telescope with triplet-lens telescope for four-level pulse amplitude modulation (PAM4) signals transmission across sub-6 GHz, millimeter-wave (MMW), and sub-terahertz (THz) bands is proposed and implemented. Polarization-demultiplexed direct detection technique enables efficient detection of unmodulated carrier in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i>-polarization (y-polarization) carrying multiple modulated carriers in the same polarization. Meanwhile, the Keplerian-triplet telescope greatly extends the optical wireless communication links. System supports PAM4 signal transmission at 6, 24, 48, and 108 GHz with data rates of 2, 10, 20, and 40 Gbps, respectively, achieving a 144 Gbps (72 Gbps/polarization × 2 polarizations) aggregate data rate. Through a cross-media of 25-km single-mode fiber, 3-km optical wireless, and either 10-m/11-m/12-m sub-6 GHz wireless or 12-m/22-m/32-m MMW/sub-THz wireless, under clear weather conditions, four PAM4 signals at two orthogonal polarizations are delivered with sufficiently low bit error rates and clear PAM4 eye diagrams. This developed fiber-wireless hybrid system presents a significant advancement in the integration of sub-6 GHz, MMW, and sub-THz communications.