Slanted TiO2 Metagratings for Large-Angle, High-Efficiency Anomalous Refraction in the Visible

Diffractive gratings are crucial elements for optical systems but suffer from rapid power drop at large angles. Recently, metagratings have shown their capability of deflecting light in an arbitrary direction. However, the experimental efficiency at large-angle is still low and the zeroth-order crosstalk is difficult to suppress. Here a new approach for large-angle and high-efficiency anomalous refraction in the visible spectrum is demonstrated. By introducing out-of-plane asymmetry, it is shown that meta-atoms with simple configurations have similar degrees of freedom as their topologically optimized counterparts. Consequently, the slanted titanium dioxide (TiO2) metagratings can steer light to 80 degrees with high relative efficiency (98.5%) and absolute efficiency (89.5%), which represents the ratio of the energy in target diffraction order to the total transmittance energy and to the total incident energy, respectively. Most importantly, the simple configurations make the TiO2 metagratings easy to fabricate, and the experimental efficiency for large (80 degrees) angle of refraction is preserved at a considerably high value of 94.0% (relative) and 83.6% (absolute). This approach represents an effective route in meta-devices and shall trigger new classes of high-performance nanophotonic systems.