A full-duplex WDM-RoF system based on tunable optical frequency comb generator

A prototype of full-duplex wavelength-division-multiplexing-based radio-over-fiber (WDM-RoF) system using a single continuous wave (CW) laser at central station (CS) is proposed and investigated. In the proposal, the tunable optical frequency comb (OFC) generator is performed by cascading an electro-absorption modulator (EAM), a phase modulator (PM) and a Mach–Zehnder intensity modulator (IM). Then the proposed OFC is used as the source of WDM-RoF network. The base station (BS) is simplified by using central carrier along with downlink multi-frequency millimeter-wave signals (MMWs). In the scheme, we obtain 21 comb lines within 0.2 dB power deviation with an interval about 10 GHz. Then we apply it to a bidirectional 1:7 WDM-RoF cellular network. For the downlink, three MMWs with frequencies of 40 GHz, 60 GHz and 80 GHz are obtained. For the uplink, 7 WDM channels carrying upstream signal are converted simultaneously. Both down and uplink delivery over 20 km transmission with less than 1 dB power penalty, which shows high spectral-efficiency and good performance over long-distance delivery.