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

A Brillouin fiber laser with low power threshold and high laser efficiency based on a 4.2-m-long As 2 S 3 chalcogenide step-index fiber is presented in this work. Due to the free-space system between the As 2 S 3 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 (UHNA) fiber which are commonly used as butt-coupling devices, the mode field adaptor (MFA) employed in this work can better match the mode field diameter and numerical aperture of the As 2 S 3 and SMF, exhibiting a total 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%. Furthermore, the Brillouin laser with the MFA butt-coupling exhibits lower relative intensity noise and phase noise and hence narrower laser linewidth than that with the lensed fiber and UHNA fiber butt-coupling. These results suggest the significance of the MFA which can reduce the cavity loss for a Brillouin laser with good performance based on As 2 S 3 chalcogenide fiber. • A low coupling loss of only 1 dB is realized by butt-coupling As 2 S 3 fiber with a mode field adaptor. • A low threshold of BFL of 14 mW is obtained based on As 2 S 3 Chalcogenide fiber. • 50 mW Stokes power is generated for a 120 mW pump power, showing a high laser efficiency of 42%. • RIN and phase noise reduction in achieved in this BFL.