| Microring resonators have potential in sensing applications due to the property of high Q-factor resonances. In this thesis, high Q-factor is pursued with detailed loss analysis and careful design of microring resonators to minimize the loss. Based on the calculation, the designed polymer microring resonators were successfully fabricated using a direct imprinting method and a template filling method. Due to the imperfection in the fabrication processes, imprinted polymer microrings have side wall roughness, which significantly influences the resonator performance. The roughness could be drastically reduced with a developed thermal-reflow technique. With the aid of thermal-reflow, microring resonators with Q-factor exceeding 104 were demonstrated. These devices were utilized in bio-sensing experiments by monitoring the resonant wavelength shift or the intensity variation at a fixed wavelength. They can also be treated to have functional binding sites for label-free detection of biomolecules. The polymer microring resonators were used in the homogeneous sensing and the surface sensing. In the homogeneous sensing, they are able to detect glucose concentration change lower than 0.1% (weight percentage); in the surface sensing, they can detect a surface coverage of 277.5 pg/mm 2 biomolecules using a model of streptavidin-biotin system. In addition, analytical expressions for the sensitivity of each possible sensing scheme were derived based on the waveguide and microring theories. Such derivation can provide significant insights in designing microring resonators for biosensor applications. |
