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.
ABSTRACT
Different types of photonic crystal components have been modeled by approximate RLC circuits. The proposed lumped circuits exploit the analogy of photonic crystal elements and RLC circuits. They are either coupled to each other or inserted like lumped circuits to imitate wave propagation within the photonic devices. Different examples such as side-coupled waveguide-cavity systems, side-coupled cavity-cavity systems, and improved structures are investigated for evaluating the theory. It is shown that the proposed circuits are exact enough to be substituted into the complicated calculations of numerical methods. In addition, the presented practical and straightforward procedure can be employed for flexible and efficient design. The results are verified using the finite-difference time-domain numerical simulations and coupled-mode theory for various devices.
