All-Optical Bistability in Photonic Crystal Slabs with Coupled Cavity-waveguide Structure

In this study, we consider a photonic crystal slab with a triangular lattice, which consists of air holes with a circular shape in a tellurium background on top of a Teflon substrate. In this structure, by enlarging the size of an air hole and infiltrating it with nonlinear polystyrene material we introduce a nonlinear cavity in the mentioned structures. Then, we optimize the geometrical parameters, using the finite-difference time-domain method, to obtain optimal parameters. The results reveal that the triangular lattice represents a nonlinear cavity with a large quality factor (). The mentioned value is much greater than the reported values in similarly designed structures. Then, the designed high-quality cavity is placed between two waveguides symmetrically, and thus a coupled cavity-waveguide structure is created. These waveguides are used to couple light in and out of the cavity. Our investigation shows that by changing the structural parameters such as distance between the cavity and waveguides, the strong coupling between the cavity and waveguides is obtained. In the end, the optical bistability diagram of the structure corresponding to optimum parameters is presented. It is observed that the threshold power is significantly low in the designed structure. In the optical switching phenomenon, the threshold intensity and the response time of the nonlinear materials are very important. The response time of polymers is significantly shorter than that of semiconductors and due to the use of polymers instead of semiconductors in the current study, the obtained results represent some advantages compared with the previously published results.