Tuning of optical resonances in asymmetric microtube cavities

We tune optical resonances in rolled-up SiO/SiO2 microtube cavities by gradually modifying the tube structure through asymmetrical postdeposition of SiO2. Spectral blueshifts followed by redshifts of the resonant modes are observed in a thin-walled microtube (tube-I), which is attributed to a competition between shape deformation and effective increase of tube wall thickness. In contrast, only a monotonic redshift is detected when asymmetrical deposition is performed on a thick-walled microtube (tube-II). Distinct wavelength-dependent tuning was revealed in both kinds of tubes. Numerical calculations based on perturbation theory are carried out to explain and confirm the experimental results. (C) 2011 Optical Society of America