Flexible polymer packaged high-Q WGM resonators for displacement detection

Whispering Gallery Mode (WGM) sensors provide high sensitivity, high resolution, small footprint, and resistance to electromagnetic interference, making them a great option for displacement sensing. An efficient method of coupling light into and out of WGM resonators is through the use of tapered tapers, but their instability can be a limitation in practical applications. Conventional packaging methods for WGM resonators use UV-curable polymers with low refractive indices to improve robustness, but their rigidity can make them less suitable for displacement sensing. Additionally, their high cost, potential toxicity and the interference from ambient moisture pose a critical issue. In this study, we demonstrate an alternative method of packaging WGM devices using non-toxic polydimethylsiloxane (PDMS). The Q-factor of 10⁷ is achieved at the 780 nm band. The PDMS packaging technique not only improves the robustness and compactness of the WGM device, but also enhances humidity resistance significantly. By take advantages of the unique flexibility of PDMS, we demonstrate displacement detection with a high sensitivity of ~0.1 pm/µm and a detection limit of 600 nm.