Eliminating Scattering Loss in Anomalously Reflecting Optical Metasurfaces

Emerging gradient metasurfaces represent a new class of diffraction optical components. Through elaborate engineering of planar arrangements of subwavelength optical antennas, metasurfaces are capable of imparting arbitrary phase profiles on to the incident light, thereby enabling devices such as holograms, complex lenses, and beam splitters. However, the traditional approach for designing reflective gradient metasurfaces fails for simple beam deflection if the angle included by the incident and the anomalously reflected beam is large. Recently, it has been shown that this shortcoming, which results from the impedance mismatch at the interface and parasitic reflections, can be eliminated by proper metasurface engineering. Here, we report the design, fabrication, and characterization of an optical metasurface, which reflects normally impinging light at around 1550 nm wavelength at an angle of 80° with respect to the surface normal. Under these conditions, the calculated and measured results show a reflection efficiency that exceeds previous results by a factor of 2. We believe that our findings are an important step toward high-efficiency devices for general wavefront manipulation.