Designing an ultra-fast all-optical full-adder based on nonlinear photonic crystal cavities

In this paper, a two-dimensional structure based on photonic crystal for adding three input bits is proposed. The dielectric rods used in this work are made of chalcogenide with a dielectric constant of 9.61. The lattice constant of the structure is 510 nm and the radius of the fundamental rods is 0.206 times the lattice constant. Three waveguides transmit the optical wave from input ports to the main waveguide. Based on the optical intensity in the main waveguide, two nonlinear cavities drop the waves toward the SUM and CARRY output ports. For using the optical Kerr effect, a rod made of the doped glass with a nonlinear coefficient of 10^–14 m²/W is placed in each cavity. The radii of these rods are 1.12 and 1.06 times the radius of the fundamental rods. To calculate the band diagram and optical wave propagation throughout the proposed structure, the plane wave expansion and the finite difference time domain methods have been used. The maximum rise time of this structure is 400 fs that is less than one for the previous works. Furthermore, the area of the structure is around 115 µm² which is proper to the optical circuits. Also, the obtained difference between margins of logic 0 and 1 is equal to 82%. According to the obtained results, one can be optimistic about the designed structure to be considered in optical processing applications.