Polarization-insensitive optical angular filtration enabled by defective photonic crystals

Optical angular filters, which can be used to filter light transmission at a specific angle, are extremely attractive for various optical applications. Here, we propose and experimentally demonstrate a one-dimensional (1D) defective photonic crystal (DPC) to realize polarization-insensitive narrow angular filtration at normal incidence. The proposed angular filter consists of a mirror-symmetric heterostructure incorporating two groups of alternatively stacked Si and SiO2 layers separated by a SiO2 defect layer. Using the plasma-enhanced chemical vapor deposition technique, the fabricated DPC can achieve a narrow angular transparency window of ±6° at the near-infrared wavelength. Based on the angular filtration effect, DPC angular filter is further demonstrated to suppress the diffraction phenomenon in the far-field projection imaging. We envision that the proposed angular filter based on DPC has potential applications in lens-less imaging, privacy protection, and beam shaping.