Power threshold reduction and laser efficiency improvement of Brillouin fiber laser based on an As2S3 Chalcogenide fiber via a mode field adaptor

Abstract A Brillouin fiber laser with low power threshold and high laser efficiency based on a 4.2-m-long As2S3 chalcogenide step-index fiber is presented in this work. Due to the free-space system between the As2S3 and single mode fiber (SMF), a high coupling efficiency is required to reduce the ring cavity loss and laser threshold, and hence improve the laser conversion efficiency. Compared with the lensed fiber and ultrahigh numerical aperture fiber which are commonly used as butt-coupling devices, the mode field adaptor employed in this work can better match the mode field diameter and numerical aperture of the As2S3 and SMF, exhibiting a coupling loss of only 1 dB. A low Brillouin laser threshold of 14 mW is achieved benefiting from the high cavity feedback of 16%. A Stokes power of ∼ 50 mW is generated for an injected pump power of 120 mW, showing a high laser efficiency of 42%.