Optimization of whispering gallery modes in microbubble resonators for sensing applications

The optical properties and sensing capabilities of fused silica microbubbles are studied numerically through a finite element method. Mode characteristics, such as the quality (Q) factor and the effective refractive index, can be determined for different bubble diameters and shell thicknesses. For sensing with whispering gallery modes, thinner shells lead to an improved sensitivity. However, the Q- factor decreases as the shell thickness reduces and this limits the final resolution. Here, we show that high resolution can be achieved when the microbubble acts as a quasi-droplet even for a water-filled cavity at the telecommunications C-band. Different sensing scenarios can be studied such as thermal sensing, pressure sensing, and nanoparticle detection. We investigate the onset of the quasi droplet regime for different modes in the microbubble.