Drop filters in a rod-type photonic crystal based on self-collimation ring resonators

We design a rod-type drop filter (RTDF) in a two-dimensional photonic crystal (2D PhC) employing self-collimation (SC) effect. The perfect 2D PhC consists of a square-lattice of cylindrical silicon rods in air. The dielectric constant and the radius of host rods are ε=12.25 (correspondingly the refractive index n = 3.5) and r=0.40a respectively, where a is the lattice constant. In such a PhC, self-collimation phenomenon occurs for transverse-magnetic (TM) light beams with frequencies between 0.176c/a and 0.192c/a. The proposed RTDF based on a self-collimation ring resonator (SCRR) consists of two beam splitters and two mirrors. The performances of the SCRR are investigated with the finite-difference time-domain (FDTD) simulation technique. The calculation results show that the transmissivity spectrum at the drop port has nearly equal peak spacing which will decreases when the geometrical length of the SCRR is increased. Moreover, the full width at half maximum (FWHM) and thus quality (Q) factor of peaks can be easily tuned by changing the reflectivity of two beam splitters.

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