Coupled-mode-induced transparency in aerostatically tuned microbubble whispering-gallery resonators

Coupled-mode-induced transparency is realized in a single microbubble whispering-gallery mode resonator. Using aerostatic tuning, we find that the pressure-induced shifting rates are different for different radial order modes. A finite element simulation considering both the strain and stress effects shows a GHz/bar difference, and this is confirmed by experiments. A transparency spectrum is obtained when a first-order mode shifts across a higher order mode through precise pressure tuning. The resulting lineshapes are fitted with the theory. This work lays a foundation for future applications in microbubble sensing.