Fig. 1. Schematic diagram of proposed birefringent metalens with ultradeep DOF. The incident linearly polarized electromagnetic wave can be decomposed into two orthogonal parts, i.e., the x-polarized (Ex) and y-polarized (Ey) beams. The birefringent metalens is able to modulate Ex or Ey independently. Holography can be applied to set several foci along the z axis (the optical axis of the metalens) for Ex and Ey beams to realize ultradeep DOF.

Fig. 2. Building blocks, and calculation and simulation results of relation between transmission amplitude and phase. (a) Schematic diagram of the triple-layered cross I-shaped meta-atom; (b) surface current distribution under the illumination of the x- and the y-polarized beams, respectively; (c) simulated transmission amplitude and phase by sweeping lx and ly at 10 GHz; (d) transmission phase coverage of single-, double-, and triple-layered cross I-shaped meta-atoms against the transmission amplitude. The insets are the schematic diagrams of the two-port networks calculated by the scattering matrix.

Fig. 3. Extinction cross-sectional spectra of the cross I-shaped meta-atoms in air for the x-polarized normal incidence. Extinction cross-sectional spectra of (a) single-, (b) double-, and (c) triple-layered cross I-shaped meta-atoms. MD represents magnetic dipole, ED represents electric dipole, MQ represents magnetic quadrupole, EQ represents electric quadrupole, MO represents magnetic octupole, and EO represents electric octupole. (d) Normalized total extinction cross-sectional spectra of single-, double-, and triple-layered cross I-shaped meta-atoms under the condition of lx=ly=3.5 mm; (e) monochromatic variation of normalized total extinction cross section with lx (ly) at 10 GHz.

Fig. 4. GSWm and the design process of the birefringent metalens. (a) Comparison of convergence characteristics under different values of p; (b) phase profiles of the x and the y polarizations by GSWm; (c) SSE curve during the phase profiles calculation process of the x and y polarizations in the metalens; normalized intensity in the xoz plane of (d) Ex, (e) Ey, and (f) E_total calculated by Fresnel diffraction theory. The normalized intensity along the z axis is shown in (g). The full-wave simulation results of the normalized intensity in the xoz plane of (h) Ex, (i) Ey, and (j) E_total; (k) normalized intensity along the z axis.

Fig. 5. Fabricated metalens and experiment results. (a) Experiment results of normalized intensities along the z axis for Ex, Ey, and E_total; (b) normalized intensities of the total scattered field by calculation, simulation, and experiment; (c) fabricated sample of the designed metalens by GSWm; inset is a zoomed-in view of the prototype; normalized field-intensity distribution for (d) Ex, (e) Ey at different longitudinal distances.

Fig. 6. High transverse-resolution imaging simulation results. (a) Full-wave simulated results of normalized intensities along the z axis for E_total under the illumination of linearly polarized spherical wave with a polarization angle of 45° at 10 GHz; (b) square pattern consisting of four discrete points; simulated field distributions for Ex, Ey, and E_total when the square pattern is placed at (c)–(e)z=400 mm, (f)–(h) z=600 mm, (i)–(k) z=1000 mm, and(l)–(n) z=1200 mm.