超构表面对非线性谐波辐射中光的自旋与轨道角动量的调控

光的自旋、轨道角动量在经典光、量子光通信、超分辨成像、光镊等领域已有广泛且重要应用。在线性光学范畴，光的自旋与轨道角动量的耦合机理已经相对成熟。在非线性光学范畴，如谐波辐射过程中如何在微纳光学器件上实现对光的自旋与轨道角动量的多维度调控，对未来的高密度光信息处理至关重要。尽管在非线性领域大家对这两个角动量已分别有所研究，然而对于二者相互耦合的机理尚缺乏系统阐述。申请人近来在倍频、三倍频辐射过程中发现超构表面的旋转对称性与光的自旋角动量存在特定的选择定则。申请人等亦首次提出并验证了超构表面上非线性光学谐波辐射过程中贝里几何相位的存在。该项目计划通过具有非线性贝里几何相位的超构单元将拓扑电荷引入超构表面，从而实现对超构表面上倍频、三倍频辐射中光的自旋-轨道角动量的同时控制。理解超构表面上谐波辐射过程中光的自旋、轨道角动量的调控机理，可为设计多维度光信息处理芯片等提供重要科学与技术基础。

Spin and orbital angular momentum (SAM and OAM) of light have broad and important applications in the classic light, quantum optical communication, super-resolution imaging, and optical tweezers and so on. In the linear optics, the coupling mechanism between the spin and the angular momentum of the light is relatively mature. However, in the field of nonlinear optics, such as in harmonic generations, how to realize the multi-freedoms manipulation of the spin and orbital angular momentum of light is essential for high capacity optical information processing in future. Although SAM and OAM of light in nonlinear optical regime have been studied separately, however, the mechanism of their mutual coupling is still lack of systematic exploration. Recently, the PI of this proposal have found that there is a specific selection rule between the SAM of second and third harmonic generations (SHG and THG) and the rotational symmetry of a metasurface. For the first time, we also proposed and verified the existence of Berry geometric phase in the process of nonlinear harmonic generations on the metasurfaces. The project plans to introduce the topological charge into the metsurface by using meta-atoms with nonlinear geometric Berry phases to achieve simultaneous control of SAM and OAM of the light in both SHG and THG processes. Understanding the mechanism of manipulation of SAM and OAM of light in nonlinear harmonic generations will provide an important scientific and technical basis for designing multi - dimension optical information processing chips.