Simple 1D metagrating by higher-order diffraction. To enhance first-order transmittance (T₋₁ or T₊₁), the light can be controlled in a large angle of propagation. The geometry parameters include grating period (Ʌ), fill factor (F) and height (H). The n_c, n_g and n_s denote refractive indices of cover, grating and substrate, respectively. Under TM polarization (i.e. H_y), zeroth-order transmittance (T₀) and T_±1 are simulated by rigorous coupled-wave analysis (RCWA) while varying the angle of incidence (θ_inc).|@|~(^,^)~|@|Angular properties of higher-order diffraction in the 1D metagrating. The optimal parameter set {Ʌ = 0.8 μm, H = 0.35 μm, F = 0.6} is determined to achieve high efficiency for T₋₁ and T₊₁ under TM polarization. Each color map shows the T₀, T₋₁ and T₊₁ spectra as the θ_inc varies from –90° to 90°. The white and yellow dashed lines indicate the first-order Rayleigh anomalies [RA_±1 (n_c) and RA_±1 (n_s)] in reflection and transmission.|@|~(^,^)~|@|Negative refraction in the 1D metagrating. (a) Transmittance spectra of T₀, T₋₁ and T₊₁ at θ_inc = 20° in the 1D metagrating. (b) Distribution of H_y (y-component of the magnetic field) simulated using the finite-difference time-domain (FDTD) method.|@|~(^,^)~|@|Asymmetric structure for 1D metagrating. (a) Schematic of the asymmetric grating where the H₁ and F₁ are height and the fill factor of the additional component from Fig. 1. (b) The T₁ map as a function of the H₁ for the asymmetric structure {Ʌ = 0.8 μm, H = 0.34 μm, F = 0.68, F₁ = 0.2} at normal incidence.|@|~(^,^)~|@|Light deflection in 1D asymmetric grating. (a) The T₀, T₋₁, and T₊₁ spectra at H₁ = 0.08 μm. (b) The H_y distribution of the right-side asymmetric grating. The grating parameter set is {Ʌ = 0.8 μm, H = 0.34 μm, H₁ = 0.08 μm, F = 0.68, F₁ = 0.2}.|@|~(^,^)~|@|Light control of the combined 1D array with left- and right-side (L and R) asymmetric grating. Schematic and H_y distribution for (a) the beam dividing and (b) the concentrating element where the grating parameter set is the same as for Fig. 5. For beam dividing (a), the L and R asymmetric gratings are located in the left and right halves of the region. For concentrating (b), their positions are reversed. To avoid disruption in the focal area in (b), 6 periods of gratings at the center are removed.

Curr. Opt. Photon. 2024;8:673~677 https://doi.org/10.3807/COPP.2024.8.6.673