Micro-Cavity Optical Sensors

Abstract

Optical micro-cavities-based sensors are the subject of intensive researches and are expected to revolutionize the sensor market especially in biological and chemical applications. In this context, a proposed form of coupled cavities is presented to enhance the performance of cavity-based sensors in terms of the range of detection and accuracy. Other applications can also use the same concept to enhance the performance like in dye lasers. The basic drawback of these micro-cavities is that they are less tolerable to technological artifacts. A good control of fabrication processes is required for proper operation. The fabrication tolerance is analyzed and experimentally characterized. The proposed coupled cavity was modelled, designed, fabricated on Si wafer based on MEMS compatible technology. Characterization of these cavities revel a widened free spectral range and high quality factor compared to conventional single cavities. In order to further understand the behaviour of micro-cavities, a model based on Fourier optics was built to take into account some effects that were not included in previous models like the small size of the mirrors, verticality, roughness, and mirror shaping. The results of this model explain some of the mismatch between the expected and measured performance. Slotted micro-mirrors are expected to solve some problems found in conventional Bragg mirrors and metallic ones. Therefore, a new model for the slotted micro-mirror was presented to include the effect of mirror small thickness and the expected multiple reflections inside it. The model results are compared to FDTD simulations and good matching was observed.