Design and optimization of an OR gate all optical circuit based on silicon photonic crystals

In this paper we investigate and optimize the design of an OR gate all optical circuit based on silicon photonic crystals. The OR gate is formed by two ring resonators placed between three waveguides, obtained by removing specific rods from the photonic-crystal structure. To optimize the design parameters, the fill factor (r/a), corresponding to the ratio between the rod radius "r" and the inter-rod lattice "a", was varied using the plane wave expansion method. The Q-factor has been determined to achieve the optimal performance of the ring resonators. The optical properties and the normalized transmission spectra for the proposed gate based on the photonic-crystal ring resonators have been calculated by the finite difference time domain (FDTD) technique. We have noted that the two rings must be symmetric to the central waveguide to obtain the OR gate function in the output.