Polarization-dependent angularly selective dielectric reflector.

A key limitation of conventional polarizers is their lack of intrinsic angular selectivity. Thus, optical devices that manipulate polarization and propagation direction are forced to realize these two degrees of freedom sequentially, increasing size and complexity. Here, we introduce and experimentally demonstrate a compact, all-dielectric optical element that simultaneously achieves polarization separation and angular selectivity. This is accomplished using a truncated three-dimensional photonic crystal that possesses a mirror symmetry and exhibits an associated symmetry band gap. For incident light aligned with the high-symmetry direction, the symmetry band gap enforces polarization-dependent reflection and transmission, whereas deviations from this orientation lift the symmetry constraint and erase the polarization selectivity. Implemented using alternating layers of silicon-rich and silicon-poor nitride etched into a cubic lattice of prisms, the structure exhibits tailorable bandwidth and low optical loss while maintaining stable performance over a wide field of view and preserving compatibility with standard nanofabrication techniques.