Analysis and modeling of a silicon nitride slot-waveguide microring resonator biochemical sensor

The performance of a recently demonstrated silicon nitride slot-waveguide microring resonator biochemical sensor is analyzed. The slot-waveguide sensor is optically modeled by using finite element method, full-vectorial and semi-vectorial finite-difference beam propagation methods. Numerical calculations are discussed and compared to the sensor experimental performance. This study includes homogeneous sensing -by using different aqueous solutions-, surface sensing -due to both, surface etching and biomolecular layer adhesion-, and power coupling characteristics of the microring sensor. It is found that all of the aforementioned numerical methods provide good agreement with the experimental homogeneous sensitivity, surface etching sensitivity and power transmission coefficient at the resonator coupling. The analysis of the surface sensitivity due to biomolecular layer adhesion suggests biomolecule polymerization on the surface of the actual device. These results demonstrate the suitability of the proposed numerical optical models and indicate that the slot-waveguide microring device can be fully wetted with aqueous analytes, which is desirable for sensing and optofluidic applications at the nanoscale.