Advancing tunable structured light with PT-symmetric dammann grating metasurfaces

Using Dammann grating (DG) metasurfaces enables miniaturization and integration of devices for generating structured light, allowing them to be used in different applications with different types or working wavelengths of structured light. However, most existing DG metasurfaces are based on Hermitian photon systems, and there has been no exploration of the results of DG metasurfaces under non-Hermitian photon system conditions. In this study, we numerically constructed a non-Hermitian DG metasurface with parity-time (PT) symmetry of the adjacent silicon dioxide substrate and lithium niobate (LiNbO3, LN) nanorods. Simulation results have demonstrated that introducing PT symmetry into DG metasurfaces alters their response wavelengths, leading to changes in the structured light patterns. To further investigate the effects introduced by incorporating PT symmetry into diffraction gratings, we have also designed two types of pseudo-Dammann gratings (PDG), namely, annular PDG and cross-shaped PDG. Incorporating PT symmetry into PDG not only improved the uniformity of the diffracted light spot arrays but also altered the distribution arrangement of the spots in one type of PDG, enabling the generation of novel and unique structured light patterns in the far field. This study theoretically proposed a PT-symmetric and dynamically tunable metasurface structure, providing a new approach for the design, control, and fabrication of dynamically adjustable optical components.