Polymer Mach Zehnder interferometers for refractive index sensing Abstract: This thesis presents polymeric Mach Zehnder interferometers (MZI) for refractive index sensing. These interferometers are designed as asymmetric Mach Zehnder interferometers (AMZIs) meaning that when compared with the conventional MZI the devices have no interaction window on the sensing arm. The asymmetricity is realized by designing the sensing arm and reference arm with different widths. The analyte of interest acting as the cladding layer covers the entire surface. The phase shift is induced by the external refractive index change due to the different sensitivities of the two arms.<br>Polymers with variable refractive index and viscosity allow great flexibility in design and fabrication. The transfer from traditional photo lithography to the roll to roll process of polymer AMZIs enables us to fabricate cost efficient sensors on a flexible platform. The thermal expansion and thermo optic co efficient of the customized polymers and PMMA substrate are characterized experimentally and the data are used in the temperature simulations of AMZIs.<br>Four design types of AMZIs using either curved tapers on the Y couplers or straight tapers on the sensing arm are presented. Extensive simulation and experimental results show the functionality of the AMZI to external refractive index change with a limit of detection (LOD) in the order 10−3 refractive index units (RIU). Temperature simulation of the AMZIs indicates a signal change of 1% per degree within temperature range 10 to 60 ◦C.<br>In addition to enhance the sensitivity of the AMZIs a simple yet efficient method is presented using tailored high index thin films on the surface of the core layer. Simulation and experimental results show that a properly placed PTFE Ta2O5 thin film can lead to enhanced sensitivity of AMZIs to refractive index changes of factors between 3 and 8. The thin films are deposited on the polymer surface using ion beam sputtering at low temperatures (< 80◦C) thereby avoiding detrimental heating effects on the substrate. It is shown that LOD of the AMZIs is enhanced by a factor 10 (down to Δn ≤ 10−4) using these films