Dual-wavelength dielectric metasurface for full-space light manipulations

Dielectric metasurfaces have been credited for their salient capability in manipulating visible light with high efficiency, yet their operations are usually specified to the transmission space with limited functionality at a specified single wavelength. In this work, we show that dielectric metasurface can also be considered as an effective platform to independently control transmitted and reflected light wavefronts with high efficiency at two distinct wavelengths. In specific, silicon meta-atoms allowing high transmission and reflection of orthogonally linear-polarized light at wavelengths of 690 nm and 750 nm along with independent 2 & pi; phase modulations are successfully established. The first demonstrated dual-functional metasurface can transform incident plane wave into focused point beam spot and focused vortex beam in transmission and reflection spaces, respectively. The spatial multiplexing strategy is further considered to enrich the functionality diversity of a single meta-device, on which two off-axis light focusing phenomena and focused vortex beams carrying opposite topological charges in either transmission or reflection spaces with reduced crosstalk are successfully witnessed. Lastly, the metasurface enabling broadband anomalous deflection further demonstrates that the device's efficiency can be further improved with densely packed meta-atoms. Our study provides a new thought in light control, which can be further considered in the development of multi-wavelength and full-space meta-devices.