Numerical investigation of tunable Fano-based optical bistability in coupled nonlinear gratings

In this paper, we numerically report the optical bistability based on tunable Fano resonances in photonic structures consisting of two coupled nonlinear slab waveguide gratings facing to each other. Quality factor (Q-factor) and asymmetric factor (q-factor) of Fano resonance of the coupled grating structure can be tuned by changing the gap-distance and horizontal shifted-alignment. The switching intensity not only depends on the Q-factor, but also strongly depends on the q-factor of the resonance. Considering strong coupling coefficients and optimizing the gap-distance between two gratings, the Fano resonance with high Q-factor and optimal q-factor can be excited. It is found that the horizontal shifted-alignment of the system provides high-order resonant mode having higher Q-factor and thus reduces the switching intensity than that of the perfect alignment system. Depending on the wavelengths of operation and q-factors of Fano resonances, the optical bistabilities will provide various switching intensities.