Parity-Time-Symmetric Forward Stimulated Brillouin Scattering Optomechanically Microwave Oscillator With LN-PM

Narrow linewidth microwave oscillators are critical components in radar, quantum precision measurement, and wireless communication systems. However, traditional optoelectronic oscillators (OEO) are prone to introducing additional noise due to the use of electrical signals, making it difficult to overcome the “electronic bottleneck” of high frequency and low stability. Generating a pure single longitudinal mode (SLM) microwave signal output with narrow linewidth and high gain remains a significant challenge. This paper proposes a parity-time (PT) symmetric all-optical optomechanically microwave oscillator (OM-MO) based on the birefringence of a z-cut lithium niobate phase modulator (LN-PM), which realizes SLM microwave photonics output with a linewidth of the order of Hz. The system utilizes the intrinsic birefringence characteristics of the z-cut LN-PM to naturally form gain and loss loops in the cavity. Precise control of the polarization state of forward stimulated Brillouin scattering (FSBS) light injected into the LN-PM triggers symmetry breaking of the PT system. Ultimately, the experiment achieved SLM microwave signal at 319.2 MHz -R07 microwave photonics (MWPs). Experiments demonstrate that the OM-MO achieves a side mode suppression ratio (SMSR) of up to 42.09 dB and a measured linewidth of 0.9 kHz at -20 dB (with an intrinsic linewidth of 45.2 Hz). Additionally, it exhibits phase noise as low as -117 dBc/Hz at an offset frequency of 10 kHz. Compared to existing PT-symmetric microwave oscillators, this scheme uses a self-excited pump source, eliminating the need for electrical signal modulation and significantly simplifying the system structure. This system provides a high-performance microwave photonics solution for applications such as radar imaging and coherent communication.