Waveguided SPR sensor using a Mach-Zehnder interferometer with variable power splitting ratio

This paper proposes and analyses the possibility of using variable power splitting Mach-Zehnder interferometer to increase the sensitivity of an integrated optics surface plasmon resonator (SPR) sensor. As the SPR sensors produces changes to both the phase and attenuation of the propagating light, this configuration is adjustable to utilize the full range of changes provided by the sensed material. Sensor sensitivity and working range can be increased by optimizing the power entering each branch of the Mach-Zehnder interferometer. Analysis of a specific SPR waveguide shows a 20% increase in sensitivity as compared to the single channel and to the conventional symmetric Mach-Zehnder setup. A very general analytic study of two configurations: variable power splitting sensor and single-channel sensor is presented, providing a decision tool as to which one would furnish the best results. As an additional outcome of our analysis we revealed that for large attenuation values in a waveguide sensor, the variable Mach-Zehnder interferometer is a preferred scheme even for a case where the sensing process causes only variations in amplitude of the optical carrier. The method is applicable to any perturbation mechanism that induces phase and amplitude changes on a waveguide.