Optical sensing by silicon slot-based directional couplers

A theoretical investigation of an optical liquid sensor, based on asymmetric directional coupler employing slot optical waveguides, is carried out. The sensing principle is based on the shift in the waveguide transmitted spectrum induced by analyte refractive index change. Silicon-on-insulator technology has been assumed in sensor design, and sensor modelling is carried out by using the coupled modes theory and the finite element method. The influence of geometrical parameters on the sensor characteristics has been investigated. A minimum detectable refractive index change of the order of 10^?6 can be theoretically predicted.