Free-Space Optical Merging via Meta-Grating Inverse-Design.

Despite various advances in achieving arbitrary optics steering, one of the longstanding challenges is to achieve optical merging for combining multidirectional beams through single-time reflection/transmission in free space. Typically, dual-directional beam merging is conducted by combining half-transmission and half-reflection using beam splitters; however, it leads to a bulky system with stray light and low merging efficiency. The difficulty of free-space beam merging lies in imparting respective distinct wavevectors to different directional beams. Herein, we originally proposed and successfully demonstrated the free-space optical merging (FOM) functionality based on the inverse-designed meta-grating architecture in the visible regime. By utilizing the inverse problem solver, two proposed meta-grating schemes experimentally enable merging of dual-directional beams into the same outgoing angle for the first time merely through single-time reflection. We envision that the creation of free-space merging performance can be widely applicable to the future optical system and facilitate the miniature optical devices and integration.