Enhancement of Modulation Depth in Radio-over-fiber Links Using Combination of Parametric Amplification and Stimulated Brillouin Scattering with Stokes Wave Feedback

Radio-over-fiber (RoF) is an attractive technology to implement high-speed mobile fronthaul networks in a cost-effective manner. In analog RoF transmission, high signal-to-noise ratio (SNR) is required, and thus lower carrier-to-signal ratio (CSR) is preferable. Nevertheless, increasing modulation depth to reduce CSR produces signal distortions during electrical-optical conversion due to nonlinear characteristics of optical modulators. The authors previously reported CSR reduction of RoF links using optical parametric amplification. Meanwhile, CSR reduction of RoF systems has been also reported using amplified Brillouin scattering. In this paper, we report CSR reduction experiments using a combination of parametric amplification in a 15-km long RoF link and stimulated Brillouin scattering (SBS) assisted by Stokes wave feedback. Reduction of CSR up to 10 dB was achieved by the proposed system, though the reduction was limited by SBS threshold of the transmission fiber without Stokes wave feedback.