Design of Polymethine Dyes with Large Third-Order Optical Nonlinearities and Loss Figures of Merit

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Science  18 Feb 2010:
DOI: 10.1126/science.1185117


All-optical switching applications require materials with large third-order nonlinearities and low nonlinear optical losses. We present a design approach that involves enhancing the real part of the third-order polarizability (γ) of cyanine-like molecules through incorporation of polarizable chalcogen atoms into terminal groups, while controlling the molecular length to obtain favorable one- and two-photon absorption resonances that lead to suitably low optical loss and appreciable dispersion enhancement of Re(γ). We implement this strategy in a soluble bis(selenopyrylium) heptamethine dye that exhibits a real part of γ that is exceptionally large throughout the wavelength range used for telecommunications, and an imaginary part of γ, a measure of nonlinear loss, that is two orders-of-magnitude smaller. This combination is critical in enabling low-power and high-contrast optical switching.