A Polarization Maintaining Evanescent Field Sensor for Measuring Liquid Refractive Index Change

摘要

A modified Mach-Zehnder interferometer (MZI) design based on elliptical silica photonic nanowires is proposed and demonstrated numerically. The MZI is used as a highly sensitive evanescent field based refractive index sensor. By applying a full vectorial finite element method, single-mode operation, polarization maintaining and very high sensitivity are achieved by simply using 800 nm-elliptical silica nanowires. Using the highly-sensitive versatile interferometry technique, the phase shift from both arms is determined and consequently the specimen's information can be retrieved. The proposed sensor is used to determine the refractive index (RI) of NaCl solutions with different concentrations. The sensor is capable of detecting a refractive index variation of the order of 10~(-6) RI unit with a high sensitivity of 4.2 rad/μm.