Inverse design of polarization-insensitive C-band Dammann grating based on dielectric metasurface

Abstract

Conventional Dammann gratings control the phase profiles of light by varying the etching depths of the DOEs, suffering from a contradiction between the fabrication complexity and the output performance. Due to the advantage of the single-step fabrication procedure, the ability to locally manipulate light at a subwavelength resolution, and the possibility of vertical integration, metasurfaces have attracted extensive interest. Here, we propose polarization-independent metasurface-based Dammann gratings that can redistribute a collimated light into high efficiency wide-angle spot arrays with desired intensity distributions. We combine a hybrid optimization algorithm with the finite-difference time-domain method to optimize the supercells of the metasurfaces. To illustrate the effective control over the power distributions among the desired diffraction orders, we first optimize metasurfaces with uniform intensity distributions. As an extension of the finding, we furthermore demonstrate metasurfaces with an intensity proportion of 1: 1.5: 2 and 1: 2. The diffraction efficiency errors are 4.67 %, 3.85 %, 1.7 %, and 9.16 % with an overall efficiency reaching 89.9 %, 85 %, 90.2 %, and 77.6 % in the four designed metasurfaces. The maximal diffraction angles for 3 × 3 and 5 × 5 diffractive spot arrays are 43.2° and 49.3° from the center. The bandwidth performance analysis demonstrates that the proposed metasurfaces show high diffraction performance in the C-band fiber telecommunications window (1530–1565 nm). Owing to the accurate modulation over intensity distributions, high diffraction efficiency, large diffraction angle, wideband characteristics, polarization-insensitive property, and single-step fabrication procedure with high etching depth tolerance, the proposed gratings may have potential applications in various regions, including optical information processing, beam shaping, and depth detection.