Channel drop filters with folded directional couplers in two-dimensional photonic crystals

In this paper, we proposed a three-port channel drop filter (CDF) with a folded directional coupler (FDC) in a two dimensional photonic crystal. The filter consists of two major parts, one is a resonator formed by a cavity defect to catch the desired signal from the bus waveguide, and the other one composed of two line defects close to form a directional coupler is to work as an frequency-dependent mirror for enhancement of the drop efficiency. The frequency response of the CDF has been derived by the couple-mode theory and the highly efficient drop conditions have been discussed. Numerical simulations obtained by the finite-difference time-domain method confirmed the feasibility of the CDF.