Fig. 1. Schematic illustration of cascaded metasurface architecture. (a) Schematic illustration of the principle. The object is placed at the input plane of the imaging system; an interferometer generates four intensity images at the imaging plane, which are the separated intensity images of LCP and RCP, as well as the intensity images of cross-polarization interferograms. By combining these four intensity images with the DHI method, it is possible to simultaneously obtain the amplitudes and phase retardation of two spin components, thereby obtaining polarization information. (b) Operation scheme of polarization division and interference induced by cascaded metasurfaces. |R⟩ and |L⟩ represent the RCP and LCP, respectively, and |x⟩ depicts the horizontal polarization. The incident light is split into four spin components (|L1⟩, |L2⟩, |R1⟩, and |R2⟩) by the 2D polarization grating placed at the spectral plane, which shifts momentums along the diagonal and antidiagonal directions, respectively. The idler light directly transmitted from 2D polarization grating is split into two spin components (|L3⟩ and |R3⟩) by the 1D polarization grating, which shift momentums along the antidiagonal direction and interfere with the orthogonal spin components |R1⟩ and |L1⟩ at the imaging plane after horizontal polarization filtering, generating interferograms I1 and I2, respectively.

Fig. 2. Design of metasurface and experimental setup. (a), (b) Geometric phase distributions of the 1D and 2D polarization gratings, respectively. Scale bar: 500μm. The insets are the local phase distributions within a 50-μm range. (c) Phase modulations of RCP (upper) and LCP (lower) components of the 2D polarization gratings along the x and y axes. (d), (e) Optical micrographs and SEM images of the 2D and 1D polarization gratings, respectively. Scale bar in micrographs: 500μm; scale bar in SEM images: 2μm. (f) Experimental setup. (g) Background intensity images without objects for calibration. The inset is a locally enlarged image of the interference image I2. (h) 1951 USAF target (Thorlabs, R1DS1N) imaging resolution test. The inset is an enlarged view of Group 4 Element 4-6, with line widths of 22.62, 25.39, and 28.50lp/mm, respectively. (i) Measured PSFs of the RCP and LCP light.

Fig. 3. Experimental results of cascaded metasurface strategy and benchmark of polarization measurement. (a)–(c) From top to bottom are the measured results of the first- and second-order LC vortex wave plates and an LC depolarizer, and from left to right are the optical micrographs and Stokes vector measurement results. These vortex wave plates are designed at the 633-nm wavelength. Scale length: 1 mm. (d), (e) Benchmarking the polarization ellipticity angle χ and orientation angle ϕ measurements of the output light after the horizontally polarized light incident on a rotating quarter- and half-wave plate, respectively. S3_T, χT, ϕT: theoretical results; S3_M, χM, ϕM: experimental results. The rotation angle intervals Δθ of wave plates are 5 deg.

Fig. 4. Real-time characterization of LC polarization grating. (a) Physical image of LC element. Red box: 1D LC polarization grating to be measured. (b) Diagram of applying an external electric field to the LC element. (c) Polarization micrograph of a 1D LC polarization grating. Scale bar: 200μm. (d) Stokes parameter distributions. (e) Phase retardation Δφ between LCP and RCP components along the dashed line in panel (d). (f) Comparison of theoretical and experimental results after unwrapping the phase retardation Δφ. The external voltage is 2.5 V (Video 1, MP4, 2.6 MB [URL: https://doi.org/10.1117/1.AP.7.1.016008.s1]; Video 2, MP4, 2.4 MB [URL: https://doi.org/10.1117/1.AP.7.1.016008.s2]).

Fig. 5. Polarimetric imaging at different wavelengths. (a) Stokes parameter distributions of light fields output from a second-order vortex wave plate in the incidences of horizontal polarization but different wavelengths. From top to bottom, the wavelengths are 633, 552, and 473 nm, respectively. (b) Comparison of S3 distributions along the angular coordinate at different wavelengths. (c) Variation trajectory of the Stokes vector along the red dashed line in panel (a) at three wavelengths. (d) Intensity ratio of the separated left- and right-handed circular polarizations (red) and diffraction efficiency (blue) with incidence of linearly polarized light at different wavelengths.

Fig. 6. Polarimetric imaging of LED illumination scenario. (a) Power spectrum of an LED source with 626-nm central wavelength and 9.2-nm bandwidth. (b) Single-shot image of a second-order vortex wave plate under the illumination of an LED source with horizontal polarization. (c) Enlarged view of interferogram corresponding to the red box in panel (b). (d) Measured Stokes parameter distributions.