Photonic RF Synthesizer Based on a Phase-Locked Optoelectronic Oscillator Using Anti-Stokes Loss Spectrum of Stimulated Brillouin Scattering

Accurate, and low phase noise RF synthesis is crucial for various applications. The phase-locked loop (PLL) is the common architecture to synthesize high spectral purity RF carriers with desired frequencies. However, the phase noise is limited by the electrical voltage-controlled oscillators (VCOs). Optoelectronic oscillator (OEO) is an alternative of RF oscillator that allows overcoming the phase noise limitation of electrical oscillator. Here, we propose a novel photonic RF synthesizer by using a voltage-controlled optically tunable OEO as VCO in a PLL. By phase-locking OEO to a tunable RF reference, tunable RF carrier with precise frequency can be synthesized. The OEO incorporates a RF photonic filter as the mode selector harnessing the light-sound interaction in a fiber, namely the stimulated Brillouin scattering. Due to the low dissipation rate of the confined acoustic wave, a narrowband anti-Stokes loss spectrum is formed, which can be transformed into a high quality factor tunable RF bandpass filter with the aid of a phase modulated optical probe wave. It facilitates the removal of the supermodes and enables the frequency tuning of OEO. Experimentally, we attain a RF synthesizer with frequency synthesis tuning range from 6 GHz to 12 GHz. The minimum tuning step is 8 Hz. At 8.4 GHz, the phase noise is −125 dBc/Hz at 10 kHz offset. The phase-locking dynamics, frequency tunability, and phase noise are thoroughly investigated. Our approach offers the prospects of low phase noise RF synthesis with wide frequency range.