Fig. 1. Bidirectional RoF system based on frequency-quadrupled vector signal generation and wavelength reuse technology

Fig. 2. Transmission spectrum of PM-FBG

Fig. 3. Optical spectrum of the 2^nd-order sideband

Fig. 4. Electrical spectrum of the quadrupled-frequency signal

Fig. 5. Optical spectra of the two branches of the PBS in Sagnac loop. (a) Lower sideband modulated by vector signal; (b) upper un-modulated sideband

Fig. 6. Optical spectra at the BS. (a) Both sidebands used for downlink; (b) unmodulated sideband prepared for uplink

Fig. 7. Electrical spectra of QPSK signal obtained by the downlink frequency beating. (a) Loaded at 24 GHz; (b) loaded at 8 GHz

Fig. 8. BER curves, eye diagrams and constellation diagrams of the BTB and 6.15 km performance. (a) Downlink with QPSK modulation; (b) uplink with OOK modulation