Design of an integrated interferometric biosensor for silicon photonics technology

The topic of this work is the family of optical biosensors based on Silicon technology. The need to develop new classes of devices able to perform in situ and real-time measurements at low cost together with the advancement in semiconductor micro fabrication technology are the main reasons for the large number of studies performed in that field. In the thesis, first of all I review the basic principles related to evanescent field sampling, together with an overview of the materials and architectures that can be exploited in this field, by extensively reviewing devices already proposed in literature, in order to better describe the theoretical concepts explored in the first part. Then, I focus my attention on the analysis and design of a Mid-Infrared imaging sensor in Silicon Photonics based on Optical Feedback Interferometry in the framework of an informal collaboration with Università di Bari and Politecnico di Bari. The system is composed by a laser source coupled to a waveguide which is then connected to a multi-branch splitter, and then refocused in a single multimode output waveguide. The relative phases of the various branches is thermally controlled by the user, allowing for a fine tuning of the spatial properties of the output beam. As a result, the user can create a single lobe output beam, whose maximum position can be electrically controlled and used for raster scan of the target, but it's also possible to create an output beam characterized by a pseudo-random pattern, suitable for single pixel imaging systems. In the framework of this activity, I designed the fundamental blocks for the multi-branch optical programmable unit, namely the splitter, the combiner, the thermal tuning regions, together with other components needed for testing and tuning, namely ring resonators. I started with the analysis of the fundamental straight waveguide, with the determination of the optimal waveguide sizes to ensure that only the fundamental transverse mode is supported, and to estimate the optical propagation losses. Using the commercial software Rsoft Synopsys CAD, I performed Finite Difference Time Domain and Beam Propagation Mode simulations of the various blocks, optimizing the dimensions of each component to maximize the output power and tunability of the system. The device designed in this thesis will be realized in the next months by a a silicon photonics fab in the framework of a multi-wafer-project.