In this paper, we will demonstrate a theoretical approach to determining the optical response of interferometric detector systems to external stimuli. The wavelength dispersion of the refractive index and the thermo-optic coefficient of transparent polymer blend waveguide materials are inserted into modeling software in order to simulate the optical response of both Multimode Interferometer (MMI) and Bragg grating (BG) architectures. The optical output of such devices is very sensitive to variations in the refractive index of the constituent materials, and they may be used to detect phenomena such as local temperature changes or relative humidity variations [1]. When the input intensity of the sensor system is normalized to unity, we demonstrate theoretical thermal sensitivities of 2 × 10−4/K for BG architectures and 3 × 10−5/K for MMI devices. A differential measurement system for BG or MMI components is discussed and simulated. We shall also discuss the use of such systems as gas detectors when a catalyst capable of accelerating the exothermic oxidation of combustible gasses is deposited onto the optical circuit.