Mid-infrared chalcogenide microfiber knot resonators

A novel type of mid-IR microresonator,the chalcogenide glass （ChG） microfiber knot resonator （MKR）,is demonstrated,showing easy fabrication,fiber-compatible features,resonance tunability,and high robustness.ChG micro fibers with typical diameters around 3μm are taper-drawn from As2S3 glass fibers and assembled into MKRs in liquid without surface damage.The measured Q factor of a typical 824μm diameter ChG MKR is about 2.84×10～4 at the wavelength of 4469.14 nm.The free spectral range （FSR） of the MKR can be tuned from2.0 nm （28.4 GHz） to 9.6 nm （135.9 GHz） by tightening the knot structure in liquid.Benefitting from the high thermal expansion coefficient of As2S3 glass,the MKR exhibits a thermal tuning rate of 110 pm·℃-1 at the resonance peak.When embedded in polymethyl methacrylate （PMMA） film,a 551μm diameter MKR retains a Q factor of 1.1×10～4.The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.