Optical bistability based on Fano resonances in single- and double-layer nonlinear slab waveguide gratings

In this paper, we numerically investigate all-optical bistable switching at low input intensity based on Fano resonances available in nonlinear slab waveguide gratings with narrow slits. Fano resonances with various quality factors (Q-factors) in the single- and double-layer slab waveguide gratings are designed and their characteristics are studied by the finite-difference time-domain method. Dependencies on wavelengths of operation, various switching intensities, contrast, and bandwidth of all-optical bistabilities are observed. Comparing nonlinear characteristics of single- and double-layer grating configurations, the latter provides more bistable efficiency with the low input intensities needed and high contrast with high Q-factors at certain operating wavelengths. Both grating configurations in this work provide interesting venues for highly efficient Fano resonance-based all-optical bistable switching devices.