Widely tunable ultra-narrow linewidth single-longitudinal-mode Brillouin fiber laser with low threshold

Abstract

A widely tunable ultra-narrow linewidth single-longitudinal-mode Brillouin fiber laser (SLM-BFL) with low threshold is proposed and experimentally demonstrated by using a 205 m long high-nonlinear fiber (HNLF) as Brillouin gain media. The single-longitudinalmode (SLM) operation is guaranteed by cascaded filters composed of a fiber ring Fabry-Pérot filter and a self-induced narrow filter based on a 4 m unpumped erbium-doped fiber. Owing to the long ring cavity, the BFL has a low threshold of 12.8 mW and ultra-narrow linewidth of 0.29 kHz. The BFL can be tuned from 1532 to 1577 nm. The optical signal-to-noise ratio of the fiber laser is higher than 70 dB during the 45 nm tune range.

All-Chalcogenide Ring Fiber Laser

“…BFLs made of silica require hundreds of meters of cavity length to reach laser threshold, leading to multi-mode operation. Hence, additional filtering is required to enable single-mode operation 6,7 . A simpler version of the silica BFL that naturally leads to single-mode operation, with reduced fiber length and reduced power threshold, can be achieved with the use of a fiber with increased Brillouin gain.…”

Optical frequency comb generation with ultra-narrow spectral lines

“…With a Brillouin gain spectrum that has a 30 MHz full width at half-maximum (FWHM), the BFL would be multimode unless additional filtering methods are implemented. The BFL single-mode operation is ensured from a series of two filtering mechanisms that suppress the many longitudinal modes of the compound ring cavity [7]. The filtering mechanisms include an in-fiber Fabry-Perot (FP) filter with a 5-m-long SMF-28 and a Sagnac loop interferometer with a 4-m-long unpumped erbium-doped fiber (EDF).…”