Inversely engineered metasurfaces for independent manipulation of transmitted and reflected light fields

Independent manipulation of transmitted and reflected light fields is a key technology for the realization of multifunctional optical applications, which can be implemented based on multilayered plasmonic or supercell subwavelength structures.However, the former is not suitable for the optical bands, while the latter is insufficient in generating large phase gradients. Here,an adjoint-optimization-based inverse design methodology is proposed, which utilizes the polarization-selective local interference between individual meta-atoms and enables monolayer dielectric metasurfaces to decouple the wavefront of transmitted and reflected optical fields. Moreover, this methodology serves to mitigate the aperiodic electromagnetic crosstalk inherent between adjacent meta-atoms, consequently leading to a significant enhancement in the performance of meta-devices. We analyzed the physical mechanism of adjoint optimization and proposed the concept of phase factors, highlighting their importance in the rapid inverse design of meta-devices—an aspect often overlooked in previous research. To demonstrate the feasibility and robustness of our method, we optimize monolayer metasurfaces with different initial structures. These devices efficiently focus and deflect x-linearly and y-linearly polarized incident light in transmission and reflection spaces, respectively.Overall, this methodology holds immense potential for designing multifunctional, high-performing metasurfaces that meet multiple constraints, opening up broad prospects for applications.