All-polymer whispering gallery mode sensor in the low-Q regime

Microcavities, such as spheres, rings or toroids, show sharp optical resonances at specific wavelengths, called whispering gallery modes (WGMs). They provide high quality factors, which leads to high sensitivity to changes in the environment, for example, due to temperature or forces. The conventional method to measure these physical quantities using WGMs is to record the resonance shift of a single microresonator. Usually an expensive low-bandwidth tunable laser system with high spectral accuracy is necessary for this. In our approach, we use an array of microspheres with slightly different diameters, taking advantage of the fact that every single microsphere has a different resonance behavior. Knowing the dependency of these intensity patterns on temperature for example makes it possible to measure changes of this quantity at a fixed wavelength. Moreover using many spheres instead of one relieves the high demands on the resonance quality and thus allows using inexpensive polymer spheres instead of high quality resonators. So, this realization of a WGM-sensor opens the perspective of simple and low cost WGM sensing.