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arXiv · 1908.07988

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

Ashutosh Patri·Stephane Kena-Cohen·Christophe Caloz
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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%.

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Ashutosh Patri, Stephane Kena-Cohen, Christophe Caloz. 2019-08-21. Large-Angle, Broadband and Multifunctional Gratings Based on Directively Radiating Waveguide Scatterers. https://doi.org/10.1021/acsphotonics.9b01319

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