Waveguide-based antireflection structure

A waveguide-based antireflection structure is proposed. The device consists of two polarization rotators (PRs), two polarization-distinguished 90-deg phase delay units (PDUs), and a polarization beam combiner (PBC). The PR and PDU, providing the same function as a quarter wave plate in free-space optics, convert a linearly polarized light into a circularly polarized light. Upon reflection from an isotropic homogenous interface, the returned light is converted back into a linearly polarized light in its perpendicular direction. Through the PBC placed at the input port, the returned light is then redirected into a different port for further use or discard. Our three-dimensional mode-matching method-based simulation shows that, on the silicon-on-insulator waveguide platform, the total device length can be made as short as 10.5 μm.