Perforated Mach-Zehnder interferometer evanescent field sensor in silicon-on-insulator

This paper investigates an evanescent field refractive index sensor based on a planar waveguide silicon-on-insulator (SOI) unbalanced Mach-Zehnder interferometer structure. The key element used for enhancing the sensitivity of the device is a waveguide structure that contains perforations through its core guiding layer. Three-dimensional numerical solution of the wave equation was used to determine optimal device dimensions and model device behavior. Devices were then fabricated in 3.4 mu m thick SOI material and optically characterized. It was found that the perforations in the waveguidc increased its sensitivity to refractive index changes in the cladding by a factor of two. The sensitivity of the device, which contained a 100 mu m long sensing region, was estimated to be 2.2 nm shift in the interferometer output spectrum per unit refractive index change of the cladding. It is expected that further optimization of the perforated waveguide structure will result in a significant increase in sensitivity.