Luminescence whispering gallery modes in Ho3+ doped microresonator glasses for temperature sensing

Abstract Optical temperature sensors based on the morphology-dependent resonant modes of Ho 3+ doped fibers and microspheres were investigated. Luminescent whispering-gallery-modes (WGMs) were detected for both the fibers and the microspheres in a contactless configuration using a modified confocal microscope to excite and detect the Ho 3+ luminescence. The WGMs were simulated by numerical solution of the Helmholtz equations and using the geometrical approximation, achieving a good agreement with the experimental results in both cases. A red shift of the spectral position of the WGMs was detected when the microresonators were heated either by contact with a regulated thermal bath or under high power laser irradiation. The thermal resolution of the WGM microresonators was advantageously compared with results reported for other rare-earth doped optical sensors based on the fluorescence intensity ratio technique.