Laser generation in an Er-doped tellurite cylindrical microresonator with effective radius variations

We demonstrate a miniature laser based on a cylindrical whispering-gallery-mode (WGM) microresonator made of erbium-doped tellurite glass. The laser is excited by a widely available broadband 976 nm laser diode and operates in the telecommunication C- and L-band spectral regions. Spatial confinement for the axially propagating modes was achieved by introducing effective radius variations (ERVs). We show wavelength tuning and band switching by selective excitation of different axial modes. The laser exhibits narrow-linewidth operation, confirmed experimentally. The results demonstrate the potential of erbium-doped cylindrical microresonators as compact, tunable, and narrow-band laser sources for telecommunication and integrated photonic applications.