Dual-function injection-locked DFB LDs in SMF–FSO–5G wireless system

This paper presents a novel bi-directional single-mode fiber (SMF)-free-space optical (FSO)-fifth-generation (5G) millimeter-wave (MMW)/sub-6 GHz wireless system that utilizes remotely injection-locked distributed feedback (DFB) laser diodes (LDs). These DFB LDs serve dual functions, enabling both the reception of 5G MMW signals and the transmission of 5G sub-6 GHz signals. The system employs phase modulation across both transmission paths, effectively reducing distortion and noise compared to intensity modulation . Experimental results demonstrate the successful transmission of downstream 10-Gbps/24-GHz and 10-Gbps/28-GHz signals, and upstream 2.5-Gbps/3.5-GHz and 2.5-Gbps/4.5-GHz signals using 16-quadrature amplitude modulation orthogonal frequency-division multiplexing. The system exhibits low error vector magnitudes and bit error rates, with clear constellation patterns and eye diagrams observed across the integrated media, comprising 40-km of SMF, 500-m of FSO, and 4-m/10-m of 5G MMW/sub-6 GHz wireless links. These findings confirm the potential of remotely injection-locked DFB LDs as dual-purpose devices for efficient bi-directional 5G communication.