  Metasurfaces have attracted extensive interests 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, we propose and experimentally
demonstrate a novel method for generating independently selective diffraction
orders. Our method is based on complex amplitude modulation with ultrathin
dielectric metasurfaces. By tailoring the geometric parameters of silicon
nanofin structures, we can spatially control the geometric and dynamic phase as
well as the amplitude simultaneously. We compare the results 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. Our developed method for achieving selective
diffraction with metasurfaces has potential applications in beam shaping,
parallel laser fabrication, and nanoscale optical detection.
