Microcapillary resonators with submicrometric wall

Microcapillary resonators are intrinsically tunable microcavities readily compatible with microfluidic systems. Whispering-gallery modes resonances of submicrometric wall capillaries exhibit large wavelength shifts as a function of the refractive index of the fluid that fills the inside. These microresonators have some unique properties as (a) the spatial separation between the surface where the total internal reflection takes place and the surface where the evanescent fields interact with the fluids and (b) the possibility of using fluids with refractive index values higher than the refractive index of the capillary material. The fabrication of microcapillaries with a submicrometric wall follows two steps. First, we prepare capillaries of about 100 mum by pulling commercial silica tubes. Second, the capillaries are pressurized and tapered down to the final diameter using a travelling-flame elongation method. The experimental characterization of these microresonators demonstrates the feasibility of different applications as chemical and biological sensors, tunable microlasers, tunable filters, etc.