Design and Analysis of 2D Photonic Crystal Devices

Abstract

In the recent few years, the photonic crystals have provided a potential platform for a wide range of applications in numerous domains. Many optical communication devices such as multiplexers/de-multiplexers, interleavers, filters etc., designed on the photonic crystals have been reported showing high throughputs. These devices have made a significant contribution in the areas of compactness, miniature sizes and fast switching etc. The photonic crystals are periodic dielectric structures which compose of alternate high and low refractive index materials. The refractive index repeats after certain period which is of the order of the wavelength of light. So, when the light waves traverse these crystals, it suffers the multiple reflections resulting in either destructive or constructive interference. The range of frequencies, due to this phenomenon becomes non permissible in the crystal. This range is known as forbidden band or photonic band gap. It is clearly visible when we plot dispersion curves of the crystal lattices. The objective of this dissertation is to design and analyze various guiding optical circuits based on the two dimensional photonic crystals. The dispersion curves of the circuits are studied with the help of Plane-Wave Expansion (PWE) method and the band gaps are found. We then create a number of point and line defects in the crystal to vanish these band gaps due to localization of the energy in the cavities formed by defects. This is done with the help of OPTIFDTD software. The power transmission curves for these structures are also investigated. The transmission of light can be studied with the help of Maxwell’s equations. The Maxwell’s equations are solved using Finite-Difference Time-Domain (FDTD) approach. These curves give the information about the path traversed by light and the power losses incurred in the waveguides. Firstly, the 2D photonic directional coupler is presented based on a square lattice. The directional coupler is optimized for its performance as a 3dB coupler with minimum losses. By introducing the appropriate defects, the coupling strength of the coupler is increased and therefore, the coupling length required is reduced at the operating length. In the second work, we investigate the design of add drop filters on two dimensional square photonic crystal lattice. The filters are based upon multiple quasi-ring cavities inside the square cavity. They are designed to have perfect drop of desired wavelengths to the specified ports and to have high drop efficiency. Thirdly, the (1x2) wavelength router, also based on the square 2D photonic crystal lattice, is investigated for its efficient iv performance. The conventional photonic waveguides of the order of lattice constant of the crystal structure are also introduced in this design for reducing the transmission losses. For all the above designed structures, the FDTD and PWE methods are implemented using OptiFDTD software, where these structures are analyzed critically from the obtained results.