Tellurite microspheres for nanoparticle sensing and novel light sources

High index Er-Yb codoped tellurite spheres with diameter of 9 μm and good sphericity were fabricated using a CO(2) laser. Upconversion modulated whispering gallery modes with a quality factor of 45,000 were observed in the sphere dipped in methanol. Refractometric sensing with detection sensitivity of 7.7 nm/RIU was demonstrated using a 9 μm diameter sphere. Such high index spheres have the potential to be used for nanoparticle sensing and mid-IR frequency conversion.