Optical Nanopatterned Heterostructure with Dual Features of Broad Spectral Distribution and Wide Spatial Diffraction for Beam Steering in Photonic Devices

A photonic heterostructure (HS) with two integrated periodicities is fabricated by combining the features of a diffraction grating and a colloidal photonic crystal. The top surface of the self-assembled photonic crystal, grown using colloids of 254 nm, is patterned with grating structures in optical disks using soft-imprint lithography. This HS, which combines the nanometric size of colloids with the micrometer 1 size of gratings, shows a large angular spread of light combined with broad diffraction peaks over the entire; visible -wavelength range, thus overcoming the strong and narrow angular selectivity of ordinary diffraction gratings. The diffraction characteristics of the HS persist with high diffraction efficiency even for oblique angles of the incident light, which is helpful in solar-energy-harvesting and lightemission devices because the diffraction angles can be steered conveniently. Numerical simulation with rigorous coupled wave analysis provides strong support for the features seen in the experimental observations.