Polarizing Beamsplitter Grating based on Asymmetric Slot Waveguide Scatterer

We demonstrate a novel design for grating-based polarizing beamsplitters (PBSs). The structure has a subwavelength thickness and is engineered to suppress all diffraction orders except for those of the desired orthogonal polarizations. This is achieved by using an asymmetric slot waveguide scatterer unit cell to ensure polarization-selective directional scattering. We first present the design rationale and demonstrate a PBS operating at ~ A = 752nm that reaches an efficiency of ~ 80% for both polarizations with a separation angle of ~ 80° between the polarized light beams. The structure has several advantages over typical grating or metasurface-based implementations, such as high efficiency at large separation angles, operation in any reflection-transmission mode (reflection only, transmission only, or both) and single periodic element requirement.