ZERO-ORDER GRATINGS USED AS AN ARTIFICIAL DISTRIBUTED INDEX MEDIUM

Zero order gratings are periodic structures with a period small compared to the wavelength of light. Only the directly transmitted light, the "zero diffraction order", is non-evanescent. It is shown, that by varying the material composition, i.e. the duty cycle of the gratings, the effective refractive index for the transmitted light can be changed. A grating with a variable duty cycle therefore behaves like an artifical material with distributed index. Based on this principle optical elements are proposed, microstructures are designed and a demonstration experiment with water waves is presented.