Photonic Crystal Three-Port Channel Drop Filter Based on One-Way Waveguide

We design a highly efficient three-port channel drop filter (CDF) with only one channel drop micro-cavity based on photonic crystal (PC) one-way waveguide. According to the coupled mode theory in time, the conditions to achieve 100% drop efficiency are derived thoroughly. The numerical results are all calculated by using the finite element method, and accord well with the theoretical analysis. Compared with previous three-port CDF based on general dielectric PC, the CDF based on PC one-way waveguide first shows almost complete channel drop tunneling at resonance via only one channel drop micro-cavity without the need for any reflection feedback.

I. Introduction

Channel drop filter (CDF) is one of the most essential components for photonic integrated circuits (PICs) and dense wavelength division multiplexing (DWDM) systems [1], [2]. The PC CDF is realized by utilizing resonant coupling between micro-cavity modes produced by point defects and waveguide modes created by line-defects, and has been researched extensively and maturely, which can be made smaller in sizes than the corresponding conventional devices [3]–[9]. In order to achieve 100% channel drop efficiency, the four-port PC CDF has been found by S.Fan, and its operating principles are that the resonator must support two degenerate modes between the two parallel waveguides [4]. The three-port CDF have also been presented by several research groups [6]–[9]. However, high channel drop efficiencies in these CDFs are all realized by means of reflection feedback due to some structural designs, which leads to additional complex design and fabrication difficulties [6]–[9]. In summation, it is impossible to achieve high channel drop efficiency for a three-port CDF by means of only one simple point-defect micro-cavity based on general dielectric PC [4]–[9].