Demonstration of High Capacity Bidirectional A-RoF System Using Wavelength Reuse and Frequency Multiplexing

We demonstrate a practical wavelength reuse bidirectional analog radio-over-fiber (A-RoF) system served by a single distributed feedback (DFB) laser. Frequency interleaving of downlink and uplink signals is proposed to ameliorate the spectral efficiency and mitigate the interference raised by the bidirectional transmission. Pre-emphasis is exploited to counteract the performance impairment brought about by the interaction between laser chirp and fiber chromatic dispersion. Through employing 64-QAM modulated 16 bands and 16-QAM modulated 12 bands filtered orthogonal frequency division multiplexing (f-OFDM) signals with 200 MHz bandwidth, asymmetric transmission with superior flexibility over 25 km fiber is attained, with an aggregate capacity of 20 Gb/s for downlink and 10 Gb/s for uplink. The mutual interference between the downlink and uplink is explored by overlapping the downlink and uplink signal spectra to varying degrees. Using the optimum frequency configuration, system performance is evaluated in terms of EVM and phase noise. To further investigate the effects caused by the Rayleigh backscattering and the stimulated Brillouin scattering (SBS), simulations are conducted on the proposed architecture, validating the conclusion from the experiment that the bidirectional transmission is primarily limited by the Rayleigh backscattering than the stimulated Brillouin scattering.