Designing of all-optical subtractor via PC-based resonators

Using a photonic crystal array, an all-optical half-subtractor has been designed that consists of four resonant rings and some waveguides which connect two input ports to output ports. The silicon rods with a period of 0.631 μm are arranged in the form of a square. Concerning the four working states of the device, different radii of nonlinear rods inside the resonators have been chosen. This issue makes the different switching thresholds for the rings and results in the correct dropping operation for optical waves. Unlike the previous works, each bit is defined to one port, and the input ports have equal power. The maximum rise time and the contrast ratio of the presented circuit are 3.5 ps and 8.45 dB, respectively. The fast response and small size are the main advantages of the presented subtractor. The obtained results demonstrates that the designed device has an acceptable performance which is proper for optical applications.