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Single-Mode Narrow-Linewidth Laser Based on Stimulated Brillouin Scattering and Parity-Time Symmetry

we propose and experimentally demonstrate a single-mode narrow-linewidth laser based on the stimulated Brillouin scattering (SBS) effect and parity-time symmetry to ensure single-mode operation. In a single cavity, we provide gain loop in the counterclockwise (CCW) direction by the SBS amplified effect, and loss loop in the clockwise (CW) direction. Then we accurately adjust the polarization controller (PC) to achieve gain and loss of the same magnitude for the CCW and CW lights. Under the PT symmetry broken condition, single-mode lasing is achieve with high stability in a long fiber laser cavity, resulting in a sub-kHz narrow linewidth.