Radio Over Fiber Links With Increased Spectral Efficiency Based on Coherent Detection and Digital Processing

Two radio over fiber (RoF) links with increased spectral efficiency based on coherent detection and digital signal processing (DSP) are studied. In the first RoF link, two independent microwave vector signals are modulated on a single optical carrier with one polarization state, transmitted over a single-mode fiber (SMF), and received at a coherent receiver. To recover the two microwave vector signals, a DSP algorithm is developed and applied to eliminate the joint phase noise from the transmitter and the local oscillator (LO) laser sources as well as the unstable offset frequency between the two laser sources. In the second RoF link, the spectral efficiency is doubled by using polarization multiplexing. Four independent 16-QAM microwave vector signals on a single optical carrier with two orthogonal polarization states are transmitted. Error-free transmission for both links is experimentally demonstrated.