Fabrication and characterization of Ge–Ga–Sb–S glass microsphere lasers operating at~1.9 μm

We report the fabrication and characterization of germanium gallium antimony sulfide (Ge-Ga-Sb-S or 2S2G, doped with Tm³⁺ ions) microsphere lasers operating at~1.9-μm spectral band. Compared to the chalcogenide glasses that are used in previous microsphere lasers, this 2S2G glass has a lower transition temperature and a higher characteristic temperature. This implies that 2S2G microspheres can be fabricated at lower temperatures and the crystallization problem in the sphere-forming process can be alleviated. We show that hundreds of high-quality microspheres (quality factors higher than 10⁵) of various diameters can be produced simultaneously via a droplet sphere-forming method. Microspheres are coupled with silica fiber tapers for optical characterizations. We demonstrate that Whispering Gallery mode (WGM) patterns in the 1.7-2.0 μm band can be conveniently obtained and that once the pump power exceeds a threshold, single-and multi-mode microsphere lasers can be generated. For a typical microsphere whose diameter is 258.64 μm, we demonstrate its laser threshold is 0.383 mW, the laser wavelength is 1907.38 nm, and the thermal sensitivity of the microsphere laser is 29.56 pm/℃.