Bloch mode engineering for photonic biosensors

• Ano de defesa: 2021
• Autor(a) principal: Arruda, Guilherme Simoneti de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: quasi guided mode resonances; biosensores fotônicos; dispositivos de uso local; guias de onda; photonic biosensors; point-of-care devices; redes de difração sub-comprimento de onda; subwavelength gratings; waveguides
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/18/18155/tde-16032021-080651/

Point-of-care (PoC) devices are an important technology in the field of medicine, playing a crucial role in healthcare by providing real time and in situ diagnostics, thus being especially suitable for regions with inadequate traditional healthcare and clinical laboratories. Photonic biosensors have advanced this area over the last few years, enabling high sensitivity, miniaturisation and mass production capability. Various configurations of these sensors have been explored, using different types of materials, such as metals and dielectrics. One of the most promising photonic biosensor configurations is the silicon waveguide based on Quasi Guided Mode Resonances (GMR), which uses a simple detection setup, and is compatible with the Silicon on Insulator (SOI) fabrication technology, thus being suitable for mass production, which is crucial for PoC devices. However, their performances are still hindered by lower sensitivities, as compared to other photonic biosensors, such as sensors based on plasmonic resonances and Subwavelength Gratings (SWGs). This dissertation proposes to find design strategies to enhance the performance of GMR sensors, without significant addition of complexity. The first step was to understand the behaviour of the silicon GMRs and SWGs for optimized structures of different geometric complexities, where the less complex is a 2D structure and the most complex is a 3D structure, typically associated with the state-of-the art devices. Using simulations in COMSOL Multiphysics, the relationship between the waveguide\'s mode confinement and sensing performance was analysed and it was realized that, depending on the light polarization, a less complex structure can achieve a performance close to the state-of-art more complex structures. A design strategy to take advantage of the high sensitivity of the SWG and simplicity of the GMR is presented. The strategy essentially perturbs the SWG period to allow coupling of guided modes with radiation modes, which greatly simplify the system, while exhibiting resonances with arbitrarily large quality factors (only limited by fabrication imperfections). The sensing performances of these new perturbed SWGs were analysed and their tolerance to fabrication deviation was estimated.