Sub-wavelength surface gratings for light redirection in transparent substrates

We demonstrate sub-wavelength grating couplers patterned on glass surfaces which are designed to convert incident free-space radiation into guided modes along the glass material. The devices are fabricated by nanoimprint lithography and the measured optical performance is compared to a simple model based on diffraction and ray-optics, and complemented by numerical simulations. We show that our approach is suitable for redirecting and guiding light over a broad range of incident angles and wavelengths in transparent substrates. The technique has potential applications for solar harvesting in window panes and display applications with minimal influence on vision quality. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4738777]