Employing a dual polarisation microring to determine refractive index and thickness of a thin polymer layer

Dual polarisation biosensing is a novel optical technique that focuses on retrieving structural information from a bound or adsorbed layer of molecules, by using a silicon-on-insulator (SOI) microring. Both density and thickness of the layer can be monitored simultaneously. Due to a self-calibrating protocol that is quickly performed at the start of every experiment, a high accuracy can be obtained. In this paper, we determine the thickness and refractive index of a thin layer of polyethyleneimine (PEI), which adsorbs to the silicon surface of the microring. This results in a layer with a thickness of 1.158 and a refractive index of 1.453 RIU.