Single-frequency hybrid Brillouin-thulium fiber laser with kilohertz linewidth

Abstract

Stimulated Brillouin scattering (SBS) is a well established method to narrow the laser linewidth to kilohertz level, which however suffers high threshold due to the low SBS gain at the region of 2 μm. The hybrid Brillouin/thulium fiber laser (BTFL) is such an approach which could suppress the laser linewidth with low threshold and high efficiency. In this paper, an ultra-narrow linewidth hybrid Brillouin/thulium fiber laser (BTFL) was demonstrated. Through experimentally optimizing the output coupling, pump scheme, Brillouin pump power and cavity length of the laser, 344-mW laser output with a narrow linewidth of 0.93 kHz was obtained, in which the linewidth of Stokes light was suppressed more than 43 times compared with the 40 kHz linewidth of the Brillouin pump. Besides, the influences of output coupling and pump scheme on the power and linewidth behavior of a single-frequency BTFL were also experimentally investigated, and there exists a performance balance among linewidth narrowing, output power and SBS threshold. The BTFL output power was further boosted to 5.5 W by a one-stage cladding-pumped fiber amplifier, and the corresponding spectral linewidth was broadened to 1.93 kHz. The output coupling exerted a significant influence on the BTFL performance.