Design of nanophotonic structures for biosensor applications

In this thesis, an optical sensor design is realized by using low symmetrical photonic crystals which support surface modes. In order to achieve low symmetry, the translational symmetry of the photonic crystal was maintained while the rotational symmetry in terms of unit cell size was disturbed. Furthermore, an air slot is placed on the surface to increase the interaction with the material to be detected. The surface mode is achieved in the band gap region by the angular displacement of the small holes in the surface and the slot added to the surface. For the proposed sensor structure, both three-dimensional frequency and three-dimensional time domain calculations were performed. A high sensitivity value of ~2100 nm/RIU was obtained as a result of the strong interaction of the material injected into the surface with the light traveling confined in the surface. A sensitivity map has been created showing different sensitivity values for different angle values and different slot widths of small holes on the surface. In addition, numerical analysis of low symmetric photonic crystal sensor structure for specific refractive index values was performed for biosensor applications. In another study conducted in this thesis, one-dimensional photonic crystal consisting of periodic arrangement of silicon and silicon nitrate with an air slot on its surface was designed for biosensor design. The biosensor structure was analyzed in both frequency and time domain. Bloch surface wave was obtained by creating a certain defect on the surface of one dimensional photonic crystal. The interaction of the light wave travelling on the surface with the material caused a shift in the resonance angle. The sensitivity of the designed structure was calculated as 258 degrees/RIU. The nano slot surface wave biosensor structure can be shown as an alternative for biosensor applications because of its high sensitivity and compactness. In another study, a new label-free optical biosensor configuration based on spectral refractive index detection method was proposed using asymmetric high refractive index contrast gratings. Characterization of the designed biosensor was carried out using two and three dimensional finite difference time domain method. Its outstanding features are its compactness, simple measurement technique, easy excitation scenario, label-free operation and high sensitivity of 450 nm/RIU. The proposed sensor configuration can give new impetus to the alternative biochemical detection approach. The last study in the thesis, eight-fold symmetric photonic quasi crystal structure sensor applications have been investigated. In order to create a waveguide in the center of the quasi-crystal structure, the diameter of the holes in the middle was increased and various waveguide modes were obtained in the forbidden band gap of the quasi-crystal structure. In addition, without defining any defects in the structure, the refractive index of certain regions of the quasi-crystal was changed at high transmission frequencies and its performance was evaluated in terms of sensor application. With the designed quasi-crystal structure, a sensitivity value of 105 nm/RIU was reached. Photonic quasi-crystal structures can be shown as an alternative for sensor applications due to the strong light-matter interaction.