Selective Diffraction with Complex Amplitude Modulation by Dielectric Metasurfaces

Metasurfaces have attracted extensive interest due to their ability to locally manipulate optical parameters of light and easy integration to complex optical systems. Particularly, metasurfaces can provide a novel platform for splitting and diffracting light into several beams with desired profile, which is in contrast to traditional gratings. Here, a novel method for generating independently selective diffraction orders is proposed and demonstrated. This method is based on complex amplitude modulation with ultrathin dielectric metasurfaces. By tailoring the geometric parameters of silicon nanofin structures, the geometric and dynamic phase as well as the amplitude simultaneously can be controlled spatially. The results are compared with a metasurface that uses a phase-only modulation, to verify such selective diffraction can be solely efficiently achieved with complex amplitude modulation. Besides, the diffraction angles of each order have been measured, which are consistent with standard grating theory. The method developed for achieving selective diffraction with metasurfaces has potential applications in beam shaping, parallel laser fabrication, and nanoscale optical detection.