Design, simulation of XOR / XNOR and AND logic gates using the optical two-circle switch

Abstract

In this paper, first, the optical two-circle switch (OTCS) and then, the XOR / XNOR and AND logic gates were designed, simulated, and optimized. The OTCS designed structure consisted of two rectangular waveguides and two optical circles between them. The light enters from one waveguide, and due to the coupling between the waveguide and the ring, it enters the circle in case of constructive interference, transmitted to the adjacent circle, and finally, transferred to another waveguide. If it is possible to change the properties of the circle in such a way that there is no constructive interference in it, the coupling of the light from the first waveguide to the circle will not occur, therefore the light will come out from the other side of the first waveguide. The continuity condition of electromagnetic fields at the boundary between rectangular and ring waveguides and the scattering condition has been used in all simulation boundaries to simulate this structure. By optimizing the size and type of material in the core and cladding the waveguides and circles, up to 90 percent of input waves were observed from the output of the second waveguide with the barium titanate core. This occurs as a result of coupling modes between waveguides and circles. In the second step, by applying transverse voltage and changing the refractive index, the conditions of constructive interference in the ring were eliminated, and the coupling between the rectangular waveguide and the circle did not occur. As a result, up to 85 percent of the light exited from the end of the first rectangular waveguide. This change of output power from the first to the second waveguide and vice versa can transform the designed structure into a two-state voltage-controlled optical switch; by putting two of these switches together in a row, optical logic gates of XOR / XNOR and AND are simulated and then optimized.