Photonic crystal filter based on defect mode and waveguide mode symmetry matching

In this paper, a new type of filter based on symmetry matching between the defect and waveguide modes in a square lattice photonic crystal for 1.31 μm wavelength is designed and evaluated. The filter consists of one elliptical defect and three wire defect waveguides with two single-mode waveguides and one dual-mode waveguide. Because the point defect state has four different resonant frequencies and four corresponding types of mode field symmetries, the proposed filter uses the match or mismatch between the defect and waveguide modes to realize two resonant frequency filtering outputs through a dual channel. To evaluate the device, the transmission characteristics of the electromagnetic waves in the device are simulated using the finite element method. The quality factor and transmission coefficient of the filter is 2,017 and 0.84 at the frequency of 0.4034 c/α (corresponding to 1.31 μm wavelength). This device can be applied to wave division multiplexing, filtering, and has the potential for applications in optical integrated chip and optical communications.