Polarization conversion of free-space light by metasurface-dressed on-chip waveguide

Emerging guided wave-driven metasurface has made outstanding contributions as bridges between guided waves and light in free space. However, people usually convert TE mode wave into y-polarization wave without achieving cross-polarization. In this work, an all-dielectric guided wave-driven metasurface was proposed and simulatively investigated, which can convert TE mode wave into x-polarization. There is a set of gradually rotating silicon single-split-rings (SSRs) embedded in a silicon nitride waveguide, which is the key of cross-polarization. Plus an array of silicon meta-atoms which can cover the full 2π phase shift, they form our metasurface together. As a proof of concept, anomalous deflection control of cross-polarized extracted wavefront and a one-dimensional focusing lens are numerical demonstrated. Our findings could lead to more flexible control of waves between free space and waveguide, and provide an ideal platform applied in photonic integrated chip.