Tunable DC-60 GHz RF Generation Utilizing a Dual-Loop Optoelectronic Oscillator Based on Stimulated Brillouin Scattering

Abstract

A dual-loop optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is experimentally demonstrated. Two lasers are utilized to realize the tunability of the OEO. One acts as the signal laser, the other is employed as the pump laser. By directly tuning the wavelength of the pump laser, a widely tunable range from dc to 60 GHz for the RF signal generation can be obtained. To the best of our knowledge, this is the widest fundamental frequency tunable range which has ever been achieved by an OEO. With dual-loop fiber lengths of 2 and 4 km, the single sideband (SSB) phase noise is measured to be −100 dBc/Hz at 10 kHz offset when the oscillation frequency is chosen as 5, 10, or 20 GHz. The side-mode suppression ratio (SMSR) is 35 dB when the oscillation frequency is 10 GHz. The stability of both frequency and power of the proposed OEO is improved with the dual-loop configuration when compared with the single-loop one. The Allan variances of the frequency fluctuation at 1-s average are $1.2\times10^{-7}$ and $4.9\times10^{-11}$ for the single-loop and dual-loop configurations, respectively. Furthermore, a phase noise model based on control theory to evaluate the SSB phase noise performance of the dual-loop OEO based on SBS is detailed for the first time. The experimental phase noise results agree well with the proposed phase noise model at an offset frequency range from 100 Hz to 100 MHz. Among different phase noise tests, the amplified spontaneous emission (ASE) noise induced by SBS is shown theoretically and experimentally to be the dominant source for the phase noise beyond 100-kHz frequency offset in the proposed OEO.