Modified periodic photonic structures for surface mode and mode converters

Photonic crystals are periodic dielectric structures that can be used for controlling the propagation of light. Recently, many researchers explore photonic crystal structures for different purposes due to their unique bandgap properties. In this thesis, various square lattice and triangular lattice photonic crystals are investigated by utilizing finite difference time domain method and plane wave expansion method. Slow light properties of optical surface modes are explored. The group refractive index and bandwidth of the structure can be arranged by manipulating the geometrical parameters at the surface. The low group velocity dispersion behavior of the surface mode photonic crystal is demonstrated. Additionally, a heterostructure which consist of asymmetric and symmetric photonic crystals is examined for the mode-order conversion purpose. The operating principle of the proposed structure is based on the phase refractive index difference between symmetric and asymmetric photonic crystal. By the help of designed configuration, at a certain frequency region fundamental mode can be converted to higher order modes. Furthermore, polarization-independent waveguide is designed by using surface mode photonic crystals. The proposed waveguide structure works for both transverse-electric and transverse ?magnetic polarizations. The light wave that has the frequency interval of surface mode can propagate with low loss along the surface of the proposed structure. The other investigated application of photonic crystals is bio-sensor configuration. In order to sense the refractive index change, surface modes are created by perturbing the surface of the photonic crystal structure in different ways. With these sensor designs, various sensitivity values are achieved. Keywords: Photonic crystals, Optical surface modes, Waveguides, Slow light, Phase shift, Polarization-independent waveguide, Sensors