This chapter presents and discusses the modeling of multilayered structures based 1D photonic crystals for micro-electro-mechanical systems (MEMS) applications. We particularly report in this chapter a design for realizing a 1D photonic crystal cavity based on highly flexible thin elastomer that enables tuning its resonance frequency by applying pressure and mechanical or thermal stress. The design consists of a Solaris thin-film elastomer layer sandwiched between two Bragg reflectors composed of six bilayers (SiO2/Si3N4). In this chapter, we will present the modeling of Bragg reflectors and photonic cavity structures using COMSOL Multiphysics, with a comparison between two COMSOL modules, Ray Optics and Wave Optics. A numerical pressure sensor based on the principles above will be presented and numerically demonstrated a resonance peak shift of 3.7 nm/bar to the lower wavelengths. An experimental MEMS Bragg mirror will also be presented, along with a photonic cavity based temperature sensor that demonstrated a transmission peak shift of 3.5 nm/° C to the higher wavelengths.