Low-Threshold and Sub-kHz-Linewidth Brillouin Laser Based on Chalcogenide Fiber at 2 μm

We experimentally demonstrate a Brillouin fiber laser (BFL) with a low threshold and narrow linewidth at 2 mu m employing a chalcogenide As2S3 fiber as the Brillouin gain fiber. The As2S3 fiber exhibits a Brillouin gain coefficient of 1.76x10(-9) m/W at 2 mu m, which is two orders of magnitude higher than that of the silica fiber, together with a Brillouin frequency shift of 6.308 GHz and a gain linewidth of 10.2 MHz. By theoretically optimizing the fiber length adopted in the Brillouin ring cavity, a 3-m-long segment of the As2S3 fiber is used to realize a BFL with excellent performance in terms of laser power threshold and linewidth. The BFL shows a total cavity loss of 6.18 dB, corresponding to a cavity feedback parameter of 24.1%. The lowest laser power threshold of 39 mW and narrowest laser linewidth of similar to 619 Hz so far, to the best of our knowledge, are simultaneously achieved for the BFL at 2 mu m. These results benefit from not only the extremely high Brillouin gain coefficient and small effective mode field area of the As2S3 fiber but also a suitable Brillouin gain fiber length and low cavity loss of the BFL. The relative intensity noise and temporal stability of the BFL are also investigated. Such a low-threshold and sub-kHz-linewidth laser will facilitate the development of practical applications such as gas sensing and coherent LIDAR in the 2 mu m spectral range.

Automated summary

This article demonstrates a low-threshold and narrow linewidth Brillouin fiber laser (BFL) at 2 μm using a chalcogenide As2S3 fiber as the Brillouin gain fiber. The BFL achieves excellent performance in terms of laser power threshold and linewidth, with the lowest laser power threshold and narrowest laser linewidth ever achieved at 2 μm. These results are attributed to the high Brillouin gain coefficient and small effective mode field area of the As2S3 fiber, as well as the optimized fiber length and low cavity loss of the BFL.