Fig. 1. (a) Schematic of the unit cell of the reflection metasurface composed of two Al structures (yellow) and dielectric layer SiO2 (blue). p=300  nm, L1=51  nm, L2=140  nm, L3=114  nm, w=50  nm; g denotes the distance between the two structures and g=70  nm. (b) Side view of the metasurface; H1=150  nm, H2=40  nm, H3=30  nm.

Fig. 2. (a) Spectral dependence of the reflection matrix coefficients. A singularity point, where r−+=0, is observed at λ=667  nm. (b) Amplitude and phase of the reflection matrix eigenvalues. Real and imaginary parts of two eigenvalues degenerate at λ=667  nm.

Fig. 3. Simulation results of the metasurface in the parameter space (L1, L3). Simulated (a) real and (b) imaginary parts of two eigenvalues at λ=667  nm. A self-intersecting Riemann surface profile and EP are observed.

Fig. 4. Amplitude and phase of CP conversion coefficients of the reflection matrix. (a), (b) Amplitude and phase of the structure for RCP incidence. (c), (d) Amplitude and phase of the structure for LCP incidence in the parameter space in the range of L1∈(0,100) (nm) and L3∈(60,160) (nm). An EP appears at (L1,L3)=(51,114) (nm) in cross reflection amplitude r−+ and cross reflection phase φ−+.

Fig. 5. Amplitude and phase of CP conversion coefficients with “0” (red curve) and “1” (blue curve) elements. (a) Amplitude of CP conversion r+− for LCP incidence, (b) amplitude of CP conversion r−+ for RCP incidence, (c) phase φ+− for LCP incidence, and (d) phase φ−+ for RCP incidence.

Fig. 6. Structure of the unit cells for the ETP and PB phase coding metasurface.

Fig. 7. Design of 1-bit coding metasurface based on ETP. Far-field scattering pattern of the coding metasurface under different incidences of (a) RCP and (b) LCP.

Fig. 8. Design of coding metasurface based on ETP and PB phase. (a) Schematic of the coding sequence. (b), (c) Far-field scattering pattern of the coding metasurface under different incidences of polarization.

Fig. 9. (a) Simulated results with L1 changed from 50 to 80 nm. The red and blue curves represent rxx and ryy, respectively. The effective length of the meta-atom in the y-direction is fixed, such that the resonance dips of rxx keep constant. The effective length of the meta-atom in the x-direction is increasing, resulting in a red shift of the resonance dips of ryy. (b) Simulated results with L3 changed from 94 to 124 nm. The effective length of the meta-atom in the y-direction is fixed, such that the resonance dips of ryy keep constant. The effective length of the meta-atom in the x-direction is increasing, resulting in a red shift of the resonance dips of rxx. Therefore, by modulating the parameters of L1 and L3, orthogonal y- and x-polarized resonances can be degenerated, which means that the generation of EP is possible.

Fig. 10. Design of 1-bit coding metasurface based on Pancharatnam-Berry (PB) phase. The far-field scattering pattern of the coding metasurface under different incidences of (a) RCP and (b) LCP light. The parameters of the structure are (L1,L3)=(81,102) (nm); the “0” and “1” elements are encoded by rotating 90°. It reveals that they exhibit identical far-field scattering for various polarization incidences, which is essentially the result of the same coding method. The PB phase imparts different phase modulations for LCP and RCP light, with the same magnitude but opposite signs. Therefore, circularly polarized light cannot be controlled independently by the PB phase only.