High contrast all-optical logic gates based on 2D nonlinear photonic crystal

We have proposed the all optical XOR, XNOR, NAND and NOT logic gates based on two-dimensional (2D) photonic crystals (PCs). In all structures the nonlinear Kerr effect has been used. The gates function is based on the destructive interference of the input signals. The phase difference between the input signals has been caused by the different signal travelling paths. To demonstrate the performance of the XNOR, NOT, and NAND gates a control port has been added to the structure. The gates have been operated at the frequency of 0.341(c/a) where 'a' and 'c' are the lattice constant and the speed of light in vacuum, respectively. Due to the maximum required input power of P0=277(mW/μm2) for the XOR, NOT, and XNOR gates and P0=554(mW/μm2) for the NAND gates, and the high contrast ratio of at least 20 dB between the ON and OFF states, these logic gates are applicable for real time communications. Simulations are based on the finite-difference time-domain (FDTD) numerical method.