An Yb³⁺-Ho³⁺ codoped glass microsphere laser in the 2.0μm wavelength regions

In this letter, an Yb³⁺-Ho³⁺ codoped sol-gel silica microsphere lasing at around 2.0μm is reported. The gain microsphere is fabricated by overlaying the 1.0 mol% Yb³⁺-0.2 mol% Ho³⁺ codoped sol-gel solution on the surface of a pure silica microsphere and is then heated using a CO₂ laser. Using a traditional fiber taper-microsphere coupling method, we observe the single- and multi-mode microsphere laser outputs around 2.0μm using a 980 nm laser diode as a pump source, with a low threshold pumping power of 14.7 mW. The ability to fabricate sol-gel codoped silica glass microlasers represents a new generation of low-threshold and compact mid-infrared laser sources for use as miniaturized photonic components for a wide range of applications including gas sensing and medical surgery.