An ultrahigh sensitivity, high resolution, aerostatic pressure sensor using microbubble resonators

Sensors based on whispering gallery resonators can push achievable sensitivities and resolutions to their limits, while maintaining minute footprints. Here, we report on the fabrication of a microbubble resonator using two CO$_2$ beams focused on a microcapillary; the resulting microbubble has an ultrathin wall. We show that, even when the wall is as thin as 500 nm, an intrinsic quality factor of $10^7$ is achievable at the telecommunications C-band. Considering strain and stress of the material, we investigate the feasibility of using the microbubble as an aerostatic pressure sensor. The measured sensitivity is 19 GHz/bar and is at the limit of current techniques. We have found that the sensitivity can be improved to 38 GHz/bar at the 780 nm wavelength range, where the resolution for pressure sensing is 0.14 mbar and the Q-factor remains higher than $10^7$.