Ultrahigh-Q WGM microspheres from ZBLAN for the mid-IR band

The advantages of high-quality-factor (high- Q ) whispering gallery mode (WGM) microresonators can be applied to develop novel photonic devices for the mid-infrared (mid-IR) range. ZBLAN (glass based on heavy metal fluorides) is one of the most promising materials to be used for this purpose due to low optical losses in the mid-IR. We developed an original, to the best of our knowledge, fabrication method based on melting of commercially available ZBLAN-based optical fiber to produce high- Q ZBLAN microspheres with the diameters of 250 to 350 μ m. We effectively excited whispering gallery modes in these microspheres and demonstrated high quality factor both at 1.55 μ m and 2.64 μ m. Intrinsic quality factor at telecom wavelength was shown to be (5.4 ± 0.4) × 10 8 which is defined by the material losses in ZBLAN. In the mid-IR at 2.64 μ m we demonstrated record quality factor in ZBLAN exceeding 10 8 which is comparable to the highest values of the Q -factor among all materials in the mid-IR.