Broadband asymmetric light transmission via all-dielectric digital metasurfaces.

We demonstrate broadband asymmetric transmission or optical-diode behavior via a digital metasurface, that is, a surface that is digitally patterned at subwavelength dimensions. Enhanced light-matter interactions at the interfaces of the metasurface break the symmetry in the propagation direction, and enables high light-transmission in one direction, while strongly reflecting the light in the opposite direction. We measured a peak extinction ratio of 11.18 dB and peak forward transmission efficiency of 74.3% at the design wavelength of 1.55μm. The operational bandwidth of the device was 201nm. We further designed, fabricated and experimentally characterized a digital metasurface that enables polarization-independent optical-diode behavior, which we believe is the first device of its kind. Our digital metasurfaces enable the optical-diode behavior in a single layer of sub-wavelength thickness for several input modes and therefore, can perform as a passive, albeit imperfect optical isolator.