Polymer-based Ring Resonators for Sensing Applications

Ring resonators, esp. when processed with well established silicon-nitride wafer technology, are already successfully applied for sensitive detection of gases and fluids. The effective refractive index is changed if molecules are present close to or adsorbed at the surface which leads to a shift in resonance frequency. Selectivity is only achieved by functionalization of the surface or by its coating with appropriate receptor molecules to guarantee that only the species of interest is accumulated at the interface. Transfer of this technique into a cost effective material system like a polymer foil is attractive for the realization of sensor networks in a large-scale, complementing other sensors for pressure, strain and temperature. Extensive simulations where performed to determine appropriate dimensions for the waveguides, the design of the ring and the coupling zone and to estimate losses. Based on these results, polymer micro-ring resonators were manufactured using microscope projection lithography. Different designs were realized using off-the shelf polymer materials. Characterization of the ring resonators themselves and their sensing performance will be discussed.