Fig. 1. Schematic plot of spin-decoupled meta-couplers endowed with triple functions of guided wave radiation, polarization demultiplexing, and dual-channel wavefront manipulation. Propagating guided waves interact with the geometric metasurfaces and are scattered out with polarization-dependent wavefronts simultaneously for two different specific functions, e.g., off-chip bi-focusing, dual-channel holography multiplexing.

Fig. 2. Illustration of the working principle of the spin-decoupled geometric meta-coupler excited by the TE guided mode. The traveling TE mode can be decomposed into the combination of LCP and RCP waves, respectively, both of which are coupled out and independently manipulated by the elaborately designed geometric metasurface with different phase profiles for function multiplexing.

Fig. 3. Numerical simulation of meta-coupler enabled off-chip polarization-demultiplexed focusing. The light propagates along the x axis from left to right as the red arrow shown. Scattered light intensity distribution in the x–z plane of the (a) LCP component, (b) RCP component, (c) total field. Light intensity distribution at the focal plane of the (d) LCP component, (e) RCP component, (f) total field. Intensity distribution along the (g) x direction and (h) y direction at the focal plane, indicating the focused beam has a near-diffraction-limited spot size. The PER at the LCP focal point and RCP focal point is evaluated at 19.2 dB and 19.7 dB.

Fig. 4. Experimental demonstration of polarization-demultiplexed focusing by a meta-coupler based on an LNOI waveguide. (a) SEM image of the fabricated Si metasurface dressed on the LNOI slab waveguide. (b) Zoom-in SEM image of the details of the metasurfaces. (c)–(e) Measured intensity distribution of the LCP component, RCP component, and total field at the focal plane. (f) Reconstructed total intensity distribution in the x–z propagation plane. (g), (h) Intensity distribution of the LCP and RCP waves along the x and y directions at the focal plane. The PER at each focal point is 15.2 dB and 13.4 dB.

Fig. 5. Simulated and experimentally constructed holographic images of the dual-channel multiplexing meta-coupler. (a), (d) The holographic images of the letter “O” with LCP, which are reproduced at z=80  μm. (b), (e) The holographic images of letter “K” with RCP reproduced at the same plane. (c), (f) The superposed two images with orthogonal polarization.

Fig. 6. (a) Real part of the guided wave electric field underneath the meta-coupler region shows small distortion. (b) Transmission intensity for different modes after the metasurface region. Only the fundamental TE0 mode is detected at the end of the waveguide.

Fig. 7. Broadband performance of the polarization-demultiplexed metalens, covering a wavelength range beyond 600 nm.

Fig. 8. Illustration of the fabrication process of the meta-coupler integrated with the LNOI slab waveguide.

Fig. 9. Schematic of the experimental setup for measurement. LP, linear polarizer; Obj, objective; QWP, quarter-wave plate; IR CCD, infrared camera.

Fig. 10. 1D light field manipulation by the spin-decoupled geometric meta-coupler in a strip waveguide. e.g., polarization-demultiplexed metalens is implemented with full-wave simulation.