Theoretical analysis of a Mach-Zehnder interferometer with a porous-film waveguide

Here we present a comprehensive theoretical study of a porous-film sensor of fluid in Mach-Zehnder configuration. It is found that the penetration of a fluid into the film pores causes amplitude and phase modulation of the interferometer output signal, maximizing the sensitivity at a certain value of the fluid refractive index. We define the Fisher information for this interferometer and show that it is a good measure of its sensitivity, hence suitable as an evaluation function in sensor optimization. We propose the sensor structure and design thin films that maximize its sensitivity to water, alcohol solutions and oils. The estimated sensitivity of the order of 10(-5) RIU to the fluid refractive index and of 5 pm to the changes in the film thickness indicate the potential of this sensor for applications in biomedicine, chemistry and environmental protection, and as a tool for the film characterization.