Theoretical Analysis of the Referencing Scheme in WGM Sensors

In a referencing scheme, some of the whispering gallery mode (WGM) sensors are functionalized for detecting particular substances and some are not functionalized for monitoring effects of unwanted perturbations. It is known that in principle the same perturbation can cause different shifts for WGM peaks with different polarizations and orders. We studied such effects using 2-D finite difference time domain (FDTD) modeling for sensing the index variations in the surrounding medium. Our results show that the assumption of referencing scheme that the sensing and reference resonators identically respond to the same perturbation holds only for the same order WGM subsets with the same polarization. This means that the application of referencing scheme requires identification of polarization and order of the WGM spectral peaks in sensing and reference resonators prior to sensing experiments.