All-polymer whispering gallery mode sensor for application in optofluidics

Microcavities such as spheres or rings are resonant optical sensors which support whispering gallery modes (WGMs). In recent years WGM based sensors have been continuously improved with respect to sensitivity and detection limit. The conventional method to measure physical as well as biological quantities using WGMs is to record the resonance shift of a single resonator. To ensure high sensitivity, resonators with high quality factors, expensive ultranarrow-linewidth tunable laser systems, and piezoelectric positioning are necessary. All these requirements hamper operation beyond the laboratory environment. To overcome these limitations in previous work we presented a small and completely polymer based measurement system. We use an array of microspheres with slightly di erent diameters, taking advantage of the fact that every singlemicrosphere has a di erent resonance behaviour. Using many spheres instead of a single one relieves the high demands on resonator quality and allows using inexpensive polymer spheres instead of high quality resonators. Here we show, that a xation of the spheres makes the device more robust with the result that the sensor is well suited for the determination of an unknown wavelength under di erent environmental conditions, for example in aqueous environment. This o ers the possibility to use the sensor in micro uidics in the future.