Enhancement of unidirectional transmission through the coupling of nonlinear photonic crystal defects

We investigate the unidirectional transmission behavior of coupled photonic crystal defects with nonlinearity by using the coupled mode theory, focusing on how to enhance the transmission contrast. Although the unidirectional transmission originates from the asymmetric configuration and nonlinear property of the structure, it is revealed that the maximum transmission contrast depends mainly on two linear factors. For two coupled defects, they are the highest order of the frequency detuning appearing in the transmission formula and the frequency splitting due to the coupling. Our analyses are supported by the numerical simulations based on the finite-difference time-domain technique. An enhancement of the maximum transmission contrast by an order of magnitude is achieved in the structure consisting of two coupled defects. (c) 2006 Optical Society of America.