Thermo-optical tuning of whispering gallery modes in Er:Yb co-doped phosphate glass microspheres

We demonstrate an all-optical, thermally assisted technique for broad-range tuning of whispering gallery modes in microsphere resonators fabricated from an Er:Yb co-doped phosphate glass (IOG-2). The microspheres are pumped at 978 nm and the heat generated by absorption of the pump expands the cavity, thereby altering the cavity size and refractive index. We demonstrate a significant nonlinear tuning range of greater than 700 GHz of both C-and L-band cavity emissions via pumping through a tapered optical fibre. Finally, we show that large linear tuning up to ∼488 GHz is achievable if the microsphere is alternatively heated by coupling laser light into its support stem.