Self-expanding fabricated optical millibubble resonators with strong thermo-optical effect

We develop a novel method for fabricating borosilicate millibubble resonators with strong thermo-optical effect. The method is based on self-expanding of air within a two ends sintered borosilicate capillary under the heating of a hydrogen–oxygen flame (HOF). The intrinsic thermo-optical effect of borosilicate millibubble resonator is experimentally demonstrated by a designed novel structure based on the principle of thermometer and the fabricated millibubble resonator has a Q factor exceeding ∼10⁴. When filled with ethanol, borosilicate millibubble resonator shows the strong intrinsic thermo-optical effect by exhibiting a linear blue shift of nearly twice of its free spectral range (FSR) under 6.0 mW pump power change, which corresponds to a thermal enhanced tuning sensitivity as high as 0.124 nm/mW. The proposed borosilicate millibubble resonator is anticipated to find applications in optical filtering, all-optical switching, microfluidic sensing as well as all-optical micro-optics devices.