Fig. 1. Schematic of mode detection HOOV mode ${\mathrm{LG}}_{\mathrm{4,2}}$ is chosen as an example. (a1) Intensity distribution of HOOV beam of ${\mathrm{LG}}_{\mathrm{4,2}}$. (a2) SSP with $F=13.4{\mathrm{mm}}^{-2}$ and $\theta =0\mathrm{deg}$. (a3) Intensity distribution of HOHG ${\mathrm{HG}}_{\mathrm{4,6}}$. (b1) HOOV ${\mathrm{LG}}_{\mathrm{4,2}}$. (b2) SSP with $F=13.4{\mathrm{mm}}^{-2}$ and $\theta =45\mathrm{deg}$. (b3) Intensity distribution of HOHG ${\mathrm{HG}}_{\mathrm{4,6}}$ after rotating 45 deg. The subscripts $(p,l)$ and $(m,n)$ are the mode numbers of ${\mathrm{LG}}_{p,l}$ and ${\mathrm{HG}}_{m,n}$. The subscript $(F,\theta )$ indicates the modulation parameters of SSP. The SSP range of the $x$, $y$ coordinate is $(-0.3\mathrm{mm},0.3\mathrm{mm})$ and $(-0.3\mathrm{mm},0.3\mathrm{mm})$, respectively.

Fig. 2. Design and fabrication of geometric metasurface. (a)–(e) Process of the phase superposition. (a) Phase distribution of the incident field ${\mathrm{LG}}_{\mathrm{4,2}}$ corresponds to Fig. 1(a1). Symbol + indicates phase superposition. (b) SSP with $F=13.4{\mathrm{mm}}^{-2}$ and $\theta =0\mathrm{deg}$ corresponds to Fig. 1(a2). The sign → indicates the result phase superposition. (c) Phase distribution of ${\mathrm{HG}}_{\mathrm{4,6}}$ corresponds to the phase of Fig. 1(a3). (d) Blazed grating phase with the period $\mathrm{\Lambda }=0.03\mathrm{mm}$. (e) Metasurface phase. (f) Unit cell of ${\mathrm{TiO}}_2$ metasurface and the structural parameters. ($\mathrm{f}0$) 3D view of nanorods. Length $L=165\mathrm{nm}$, width $W=65\mathrm{nm}$, height $H=500\mathrm{nm}$, and period $T=200\mathrm{nm}$. $(\mathrm{f}1)-(\mathrm{f}4)$ Top view of the nanorods corresponds to four characteristic phase rotation angles $\phi =0$ (180 deg), 46.8, 83.6, and 105.3 deg. The red plus sign + indicates the center of the structure. (g) Phase value of the four characteristic corners of the nanorods at the corresponding design wavelengths of 405, 532, and 633 nm. Color corresponds to the corresponding wavelength. (h) Metasurface device corresponding to phase diagram (e). Optical microscope image of the metasurface with a radius of $300\mu \mathrm{m}$ (Olympus objective, magnification $10\times$, numerical aperture $\mathrm{NA}=0.5$, $\text{scale bar}=50\mu \mathrm{m}$). The red dotted frame shows a partially enlarged view of the central phase optical microscope image (Olympus objective, magnification $100\times$, numerical aperture $\mathrm{NA}=0.95$). Plus sign + indicates the center of the metasurface corresponding to (f) symbol +.

Fig. 3. Experimental results of multiwavelength HOOV detection. (a) Schematic of optical field diffraction of the metasurface. Three wavelengths ${\lambda }_1=405\mathrm{nm}$, ${\lambda }_2=532\mathrm{nm}$, and ${\lambda }_3=633\mathrm{nm}$ combined optical incident with left-handed circular polarization. The dotted line corresponds to wavelength color. Three-color sample drawing villains represent the photons of three wavelengths. ${\varphi }_{\lambda i}$ is the diffraction angle at three wavelengths. The target detection field ${\mathrm{HG}}_{\mathrm{4,6}}$ appears at three different diffraction azimuths ${\varphi }_{\lambda 1}=19.72\mathrm{deg}$, ${\varphi }_{\lambda 2}=26.31\mathrm{deg}$, and ${\varphi }_{\lambda 3}=31.94\mathrm{deg}$, which accompany a right-handed circular polarization state. (a1)–(a3) Diffraction field of the target detection field ${\mathrm{HG}}_{\mathrm{4,6}}$ at three wavelengths. (a1) Detection diffraction field at the design wavelength ${\lambda }_1=405\mathrm{nm}$. (a2) Diffraction field at ${\lambda }_2=532\mathrm{nm}$. (a3) Diffraction field at ${\lambda }_3=633\mathrm{nm}$. The Cartesian coordinate system is represented by the black dotted line with a single arrow. The red solid arrow line indicates the $z$ axis direction. The dotted line double arrow indicates the position of the target detection field on the CCD. (b) Simulated polarization transformation efficiency of metasurface in the visible light band (from 400 to 700 nm) and the experimental measured data points at three wavelengths ${\lambda }_1=405\mathrm{nm}$, ${\lambda }_2=532\mathrm{nm}$, and ${\lambda }_3=633\mathrm{nm}$. The black solid line is the calculated data for the entire visible band. The circular data points are the calculated values at three wavelengths. Triangular data points are the experimental data (color corresponds to wavelength). (c) Gray code pattern based on metasurface detection ${\mathrm{LG}}_{4,2}$ mode with three-wavelength switches. (c1)–(c8) Gray code images 111, 110, 101, 011, 100, 010, 001, and 000 corresponding to binary numbers 5, 4, 6, 2, 7, 3, 1, and 0, respectively. The white number group is the gray code array. Cyan numbers are binary numbers. The colored circular arrow curve indicates the polarization state of the corresponding wavelength.

Fig. 4. Schematic diagram of the experimental setup.