Photonic crystal bends and power splitters based on ring resonators

In this paper, theoretical and numerical analysis of low-loss right angle waveguide bends and T-junctions based on ultra-compact photonic crystal ring resonators (PCRR) is presented. Desirable characteristics are obtained by designing the waveguide bends and T-junctions as low-Q resonant cavities with certain symmetries and small radiation loss. A simple analysis, based on coupled mode theory (CMT) in time, is used to explain the operation principles which agree qualitatively with the numerical results. These structures have high transmission efficiency over a large bandwidth in third communication window. Also effects of changing the ring size on power splitter transmission characteristics are discussed. The perfect transmission and zero reflection conditions are discussed by applying coupled mode theory. Results obtained by the finite difference time domain (FDTD) simulations are consistent with those from the coupled mode theory.