High-Sensitivity Flow Rate Sensor Enabled by Higher Order Modes of Packaged Microbottle Resonator

In this letter, we demonstrate a high-sensitivity flow rate sensor which is packaged using a stable and convenient method. The sensor is based on an optofluidic microbottle resonator (OFMBR), which serves as a promising platform for fluid sensing due to its ultrahigh quality factor and inherent microfluidic channel. The coupling system is packaged using a modified method, and the sensor’s stability is verified using phosphate buffered saline at different flow rates. According to the Bernoulli effect of fluid, the dynamic change of velocity in OFMBR can be detected via wavelength shift mechanism of whispering galley mode. Both the simulated and experimental results show that sensitivity can be enhanced for a given wall thickness by exploiting higher order radial modes of the OFMBR. The maximum sensitivity of 0.079 pm/( $\mu \text{L}$ /min) within the range of 0- $200~\mu \text{L}$ /min is achieved in the experiment. This sensor provides an optional method for fluid detection with high sensitivity and stability.