Surface mode biosensor and waveguide in photonic structures

In this thesis, first of all, the design of a polarization-independent (dual-polarization) waveguide is presented by utilizing surface modes of photonic crystals. The waveguide structure operates in a frequency interval that is commonly shared by both TE and TM polarizations. The numerical calculations based on PWE and FDTD methods are carried out to design and demonstrate a surface mode waveguide that provides confinement and guiding for both TE and TM modes. Once the relevant modes are properly excited, the high transmission efficiency of the photonic crystal surface waveguide is ensured. The demand to have polarization-insensitive devices makes the proposed design an important component for the photonic integrated circuit applications. Moreover, a broadband surface mode photonic crystal waveguide is proposed with a bandwidth value of 28% for only TE polarization. In addition to polarization insensitive waveguide design, a new bio-sensor concept that incorporates photonic crystal (PC) surface modes to sense small refractive index changes is designed and presented. The initial attempt creates optical surface modes by first enlarging and then perforating the radii of rods residing along the end surface of the square-lattice PC. The strongly confined mode which decays both evanescently along transverse to propagation direction interacts with the substance while propagating along the PC-air interface. Due to index change of the ambient medium, the transmission spectrum experiences linear shift with a large dynamic range. The relocation of the surface defects enhances the sensitivity of bio-sensor from ~8 to ~93 nm/RIU. The second type of investigated PC structure is based on triangular-lattice PC and it provides a surface state bio-sensor with a sensitivity of 117 nm/RIU. In addition to these designs, a final structure that incorporates air slot along one side of triangular-lattice PC is proposed. Succeeded sensitivity value is 396 nm/RIU. The investigation shows that even higher sensitivities can be achieved. The different RIU values are reminiscent of group velocity of the relevant modes which can be extracted from the dispersion analysis. Compact, sensitive and label-free optical sensors based on surface modes may become part of the important applications in opto-fluidic technology and lab-on-a-chip. Keywords: Photonic crystals, Polarization-insensitive waveguides, Optical surface modes, Wide bandwidth waveguides, Sensors, Integrated optics, Waveguides.