A high-drop hole-type photonic crystal add-drop filter

Based on the effect of total internal reflection (TIR) and photonic band gap, a new type of hexagonal-lattice hole-type silicon photonic crystal add-drop filter is proposed with a large circular hole as inner ring. The single mode operation is realized by compressing the two rows of photonic crystal above and below the line defect waveguide. Two-dimensional (2D) finite-difference time-domain (FDTD) method is then applied to investigate the impacts of side length of inner ring and coupling strength on its drop efficiency. It is also fairly compared with the traditional inner ring structure composed of hexagonal-lattice holes. The results show that the proposed structure can offer higher spectral selectivity than the traditional one. Two channel wavelengths of 1.425 μm and 1.45 μm can be simultaneously dropped at corresponding ports with drop efficiency of more than 90% and quality factor of 900 in the proposed configuration when the width of bus waveguide, the side length of inner ring and the coupling strength are 0.8 √3a, 4a and 0, respectively, where a is the lattice constant.