High-Q, ultrathin-walled microbubble resonator for aerostatic pressure sensing

Sensors based on whispering gallery resonators have minute footprints and can push achievable sensitivities and resolutions to their limits. Here, we use a microbubble resonator, with a wall thickness of 500 nm and an intrinsic Q-factor of 107 in the telecommunications C-band, to investigate aerostatic pressure sensing via stress and strain of the material. The microbubble is made using two counter-propagating CO2 laser beams focused onto a microcapillary. The measured sensitivity is 19 GHz/bar at 1.55m. We show that this can be further improved to 38 GHz/bar when tested at the 780 nm wavelength range. In this case, the resolution for pressure sensing can reach 0.17 mbar with a Q-factor higher than 5×107.