Real-Time $4\times 3.5$ Gbps Sigma Delta Radio-over-Fiber for a Low-Cost 5G C-RAN Downlink

A 4-lane proof-of-concept real-time sigma-delta-over-fiber system targeting 5G C-RAN downlink is demonstrated using off-the-shelf components. Per lane, an EVM of 2.67% is achieved for a 3.5 Gbps 256-QAM signal modulated at 3.5 GHz over 20-km single-mode fiber at 1310 nm.