We discuss the peculiar properties of binary waveguide arrays composed of identical photonic crystal waveguides with nonuniform spacing. Coupled-mode theory is used in order to demonstrate that, as a result of the excitation of the individual waveguides’s modes, two different array modes characterized by opposite transverse velocity can propagate. Approximated expressions for the evaluation of the diffraction curves and the percentage of energy carried by each array mode are calculated and tested through numerical examples.
© 2008 Optical Society of America
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