Narrow Linewidth All-Optical Optomechanically Microwave Oscillator Based on Forward Stimulated Brillouin Scattering

An narrow linewidth all-optical optomechanically microwave oscillator (OM-MO) based on forward stimulated Brillouin scattering (FSBS) for microwave photonics (MWPs) generation is proposed and demonstrated. The all-optical OM-MO consists of a 100 m SMF ring cavity which provide FSBS gain and a Sagnac loop with 10 m un-pumped Erbium-doped fiber (EDF) that used as saturable absorber. At 280 mW 980 nm pump threshold power, the 128∼368 MHz tunable range with about 50 MHz frequency interval of the MWPs are achieved by adjusting PCs to tune the offset frequency between the repetition rate of the driving pulse and the R ₀₃ –R ₀₈ FSBS acoustic mode resonance frequency of the all-optical OM-MO. At the same time, the acoustic and side-mode suppression rates of R ₀₃ –R ₀₈ acoustic mode based R ₀₃ –R ₀₈ MWPs are 21, 28, 22, 28, 31, 27 dB and 38, 28, 20, 30, 30, 32 dB respectively. Compared with the FSBS based OEO and passively mode locked fiber laser, the all-optical OM-MO in longer length fiber without any electrical microwave devices can generate narrower linewidth MWPs by narrowing the passive resonator intrinsic linewidth, which is different from the backward Brillouin fiber laser of narrowing pump linewidth. The linewidths of R ₀₃ –R ₀₈ MWPs are 11.9, 11.1, 10.3, 10.8, 10.4, 10.5 Hz. Within 20 minutes of the stability experiment, the power and frequency stability fluctuation of the R ₀₄ MWP are ±0.5 dB and ±5 kHz respectively. The best phase noise value at 10 kHz frequency offset is −136.1 dBc/Hz of R ₀₄ MWP which is superior to FSBS based OEO. This narrow linewidth MWP generation technology can be promising for radar monitoring and wireless communication applications.