Sub-Kilohertz Narrow Linewidth Fiber Laser Based on Nanoparticles Doped Self-Injection Module

Fiber lasers with narrow linewidth are essential light sources for many prospects in advanced scientific fields. In this letter, we proposed a scheme of self-injection locked single-frequency fiber laser based on a hybrid cavity configuration and a novel type of nanoparticles doped fiber. The newly proposed hybrid cavity was applied to achieve mode selection in the case of a long cavity which helped increase output power without sacrificing mode instability and single frequency performance. The nanoparticles doped self-injection module helped achieve a fiber laser with 3dB linewidth compressed from 16 kHz to 497 Hz and side mode suppression ratio of more than 60 dB. Furthermore, the sub-kilohertz fiber laser was amplified to more than 1 W with the polarization extinction ratio of
$\sim $
30 dB. Throughout the work, experimental verification and analysis have been carried out to confirm the single frequency lasing performance, including center wavelength drift and slope efficiency variation. The demonstrated watt-level narrow linewidth fiber laser with low RIN and frequency noise has full potential for practical applications.