Packaged Microbubble Resonator for Versatile Optical Sensing

Microbubble whispering-gallery resonator with the intrinsic microfluidic channel is a promising platform for biochemical sensing due to their ultrahigh quality (Q) factor and ultralow detection limit. In this work, we realize a packaged microbubble resonator (PMBR) of ultrahigh-Q factor (∼ 3.52×10 $^6$ ) in a moisture curable polymer for practical applications. The long-term stability and thermal response of a PMBR are measured. Further, we demonstrate the dynamic hydrogel gelation transition from hydrophilic to hydrophobic state by detecting the resonant wavelength shift and mode broadening in a filled PMBR simultaneously. The refractive index changes of hydrogel during the transition is explicitly modelled. Our work shows the versatility of PMBR for practical optical sensing and may open a new route to microfluidic dynamic reaction.