  Polarization beam splitters, devices that separate the two orthogonal
polarizations of light into different propagation directions, are one of the
most ubiquitous optical elements. However, traditionally polarization splitters
rely on bulky optical materials, while emerging optoelectronic and photonic
circuits require compact, chip-scale polarization splitters. Here we show that
a subwavelength rectangular lattice of cylindrical silicon Mie resonators
functions as a polarization splitter, efficiently reflecting one polarization
while transmitting the other. We show that the polarization splitting arises
from the anisotropic permittivity and permeability of the metasurface due to
the two-fold rotational symmetry of the rectangular unit cell. The high
polarization efficiency, low loss, and low profile make these metasurface
polarization splitters ideally suited for monolithic integration with
optoelectronic and photonic circuits.
