Large-Angle, Broadband and Multifunctional Gratings Based on Directively Radiating Waveguide Scatterers

TL;DR

This paper introduces a novel design for large-angle, broadband, multifunctional diffraction gratings using asymmetric waveguide scatterers, achieving high efficiency and additional functionalities like polarization splitting.

Contribution

The authors present a new grating design based on asymmetric waveguide scatterers that enables high-efficiency large-angle deflection and multifunctionality, surpassing conventional surface-relief gratings.

Findings

Achieves diffraction efficiencies up to 94% at 47° deflection

Operates broadband with strong tolerance to incident angle variations

Demonstrates multifunctionality with an 80° polarization beamsplitter

Abstract

Conventional surface-relief gratings are inefficient at deflecting normally-incident light by large angles. This constrains their use in many applications and limits the overall efficiency of any optical instrument integrating gratings. Here, we demonstrate a simple approach for the design of diffraction gratings that can be highly efficient for large deflection angles, while also offering additional functionality. The gratings are composed of a unit cell comprising a vertically-oriented asymmetric slot-waveguide. The unit cell shows oscillating unidirectional scattering behavior that can be precisely tuned as a function of the waveguide length. This occurs due to interference between multiple modes excited by the incident light. In contrast to metasurface-based gratings with multiple resonant sub-elements, a periodic arrangement of such non-resonant diffracting elements allows for broadband operation and a strong tolerance for variations in angle of incidence. Full-wave simulations show that our grating designs can exhibit diffraction efficiencies ranging from 94% for a deflection angle of 47$^\circ$ to 80% for deflection angle of 80$^\circ$. To demonstrate the multifunctionality of our grating design technique, we have also proposed a flat polarization beamsplitter, which allows for the separation of the two orthogonal polarizations by 80$^\circ$, with an efficiency of 80%.