High sensitivity and large measurement range refractometric sensing based on Mach-Zehnder interferometer

An on-chip refractive index (RI) sensor with high sensitivity and large measurement range is demonstrated. The sensing scheme presented here is based on Mach-Zehnder interferometer configuration built on an SOI wafer. The measured wavelength sensitivity reaches 3498.6 nm/RIU (TE-mode). Meanwhile, according to the period changes of interference patterns, the measured period sensitivities are 20.4 nm/RIU (TE-mode) and 61.1 nm/RIU (TM-mode), respectively. Therefore, the fine index change detection limit reaches up to 1.1×10
^-5
RIU, while the period shift for larger index change detection has a measurement range of several RIU. By making an array, the proposed on-chip sensor has a potential application for multiple samples detection, such as chemical and bio-toxins in drinking water ranging from sub-nanogram to picogram level.