CROW-based Fano structures for all optical switching devices

Abstract

In this paper, an improved optical Fano switch based on coupled resonator optical waveguides (CROWs) is presented. The new topological design is employed to achieve steeper and highly asymmetric Fano resonances (FRs). Physically, in the proposed structures, due to the increase in the effective refractive index at the center of the CROW, a confined mode arises in the continuum background according to the variational theorem and leads to FR. The results show that in CROW-based Fano switches, the Fano spectrum is improved by tuning the number of nanocavities. The ratio between the slope ratio and linewidth shows an improvement of 55.25% from single to CROW5. As an important application of FR, an ultra-compact device with a CROW-based Fano structure is demonstrated. The results of the numerical finite difference time domain simulation agree well with the theoretical coupled mode theory.