Zeroth-order-free holographic reconstruction with a nanoimprinted nonlocal metasurface

Abstract

The undesired zeroth-order diffraction (ZOD) arising from imperfections in diffractive optical elements (DOEs) degrades the quality of target optical wavefronts. Herein, we propose a zeroth-order-free holographic reconstruction method using a nanoimprinted nonlocal metasurface. By judiciously designing the metasurface structure and its angular selectivity based on guided mode resonance, the ZOD can be suppressed without relying on a bulky, conventional 4f setup. We designed and fabricated a nanoimprinted nonlocal metasurface using a high-refractive-index TiO2-composite resin. Using the metasurface, we demonstrated ZOD suppression in a surface-relief DOE and a spatial light modulator. Furthermore, we prototyped a 20-mm-square metasurface and verified its effectiveness in suppressing the ZOD in 3D holographic projection.

Figures (7)

• Figure 1: Schematic of ZOD suppression using (a) the proposed method employing (b) a nonlocal metasurface based on guided mode resonance. (c) The corresponding 2D angle‑dependent transmittance. (d) Conventional ZOD suppression using a 4f setup.
• Figure 2: Design and fabrication of the nanoimprinted nonlocal metasurface. (a) Angle‑ and wavelength‑dependent transmittance of the designed metasurface. (b) Wavelength- and (c) angle‑dependent transmittance profiles along the dashed and dash‑dotted lines in (a). (d) Fabrication flow based on nanoimprint lithography.
• Figure 3: Characterization of the fabricated metasurface. (a) Photograph of the fabricated sample. (b) 3D structure measured using an atomic force microscope together with the corresponding (c) cross‑sectional profile at the center. (d) Measured wavelength‑ and angle‑dependent transmittance. (e) Wavelength‑dependent transmittance for normal incidence ($0^\circ$). (f) Optical setup for evaluating the in‑plane angular selectivity of the sample, and (g) the corresponding evaluation results.
• Figure 4: Experimental validation using a surface‑relief DOE. (a) Ideal phase distribution of the designed surface‑relief DOE. (b) Photograph of the fabricated element. (c) 3D surface profile measured with a confocal laser microscope. (d) Experimental setup. (e, f) Simulated diffraction pattern produced by the ideal element. Experimentally obtained diffraction patterns (g, h) without and (i, j) with the metasurface.
• Figure 5: Holographic projection system based on (a) 4f and (b) free-space setups. (c) Example phase hologram displayed onto a phase-only SLM.