Suppression of Brillouin scattering-induced noise in long-haul high-power RoF links via non-uniformly distributed four-tone phase modulation.

An approach to suppressing Brillouin scattering-induced noise in long-haul high-power radio-over-fiber (RoF) links is proposed via non-uniformly distributed four-tone phase modulation. Four single-tone signals with uneven frequency intervals are utilized to phase modulate the optical signal before transmission. The power transferring from the optical carrier to the non-uniformly distributed modulation sidebands largely suppresses the Brillouin scattering-induced relative intensity noise (RIN). In the experiment, transmission of a 64-QAM wireless communication signal centered at 10 GHz and with a bandwidth of 100 MHz is demonstrated. The threshold of the stimulated Brillouin scattering (SBS) in a high-power RoF link involving a spool of a single-mode fiber (SMF) with a length of 20.5 km is increased by 11 dB based on this scheme, compared with that without phase modulation. Under an input optical power of 19 dBm, the error vector magnitude (EVM) and the adjacent channel leakage ratio (ACLR) are optimized from 34.39% to 1.32% and from -20.73 dBc to -35.32 dBc, without and with phase modulation, respectively. This scheme paves a way to realizing long-haul high-power RoF links for efficiently transmitting broadband wireless communication signals in cloud radio access networks (C-RANs).