add-drop and channel-drop optical filters based on photonic crystal ring resonators

here, we propose an add-drop and a channel drop filter based on two-dimensional photonic crystal all circular ring resonators. these structures are made of a square lattice of silicon rods with the refractive index n1=3.464 surrounded by air (with refractive index n2=1). the broadest photonic band gap occurs at the filling ratio of r/a = 0.17. two linear defect w1 waveguides couple to the ring. our add-drop and channel drop filters form by the appropriate coupling distance between the ring and waveguide. the dropping efficiency of both filters in their operational window - the c (1.535-1.565μm) and l (1.565-1.625μm) bands of optical telecommunications - is almost %100 and corresponds to a deca-pole degenerated resonant mode. normalized frequencies (a/λ), in degenerated mode equal to 0.3684 and 0.3645. resonant modes of the all circular ring resonator with their corresponding degenerated poles and the transmission spectra are calculated using the pwe, and 2d-fdtd methods respectively.