High-power high-performance radio-over-fiber link for minimalist wireless base station

Broadband minimalist wireless base stations without energy-consuming electrical power amplifiers are the rosy scenario of the next-generation wireless communication systems. High-power radio-over-fiber (RoF) links, which are featured by large operation bandwidths, are regarded as the supporting technology for realizing such a vision. Nevertheless, the severe signal-to-noise ratio (SNR) deterioration induced by the second Brillouin scattering in high-power and long-distance RoF links must be first solved. Here, an approach to suppressing the secondary Brillouin scattering-induced SNR deterioration in high-power long-distance RoF links is proposed and demonstrated based on phase modulation driven by a sinusoidal signal. In the proof-of-concept experiment, the Brillouin threshold in a high-power RoF link involving a spool of single-mode fiber (SMF) with a length of 10 km is increased by more than 5 dB with the assistance of phase modulation. The SNR is improved by 31 dB when the optical power injected into the SMF is 22 dBm. In addition, the error vector magnitude (EVM) is optimized from 31.71% to 0.62% for transmitting a 256-QAM wireless communication signal with a center frequency of 5 GHz and a bandwidth of 6.75 MHz in this RoF link under the injected optical power of 22 dBm. Based on this high-power RoF link, a minimalist wireless base station utilizing a photodetector-direct-drive antenna is realized. This scheme is feasible for transmitting broadband wireless communication signals, where a 64-QAM orthogonal frequency division multiplexing (OFDM) wireless communication signal with a center frequency of 10 GHz and a bandwidth of 400 MHz has achieved high-quality transmission in this high-power RoF link under an injected optical power of 22 dBm.