The first Janus metasurfaces convert asymmetric orbital angular momentum directionally from arbitrary spin angular momentum. Titania-based meta-atoms enable operation in the visible range. These meta-atoms also offer local and global rotation, as well as width control, achieving multifunctionality in a single-layer design, surpassing previous approaches based on spatial multiplexing or vertical stacking.
Janus metasurfaces, offering versatile light manipulation contingent on incident direction, are explored across microwave to mid-infrared spectra. Nonetheless, prior designs often resort to spatial multiplexing or vertical stacking, entailing complex fabrication. Metallic Janus metasurfaces, owing to material properties, suffer notable Ohmic losses in the visible spectrum. In this study, Single-layer TiO2-based Janus metasurfaces with arbitrary polarization control is experimentally demonstrated, exhibiting directionally asymmetric functionalities in spin and orbital angular momentum (OAM). A novel Jones matrix formulation tailored for Janus metasurfaces is presented, enabling efficient generation of two asymmetric, high-purity OAM states of vortex beams at wavelength of 532 nm, contingent on incidence direction. This innovation facilitates compact and versatile phase manipulation, encompassing applications such as lasers and optical combiners, thereby expanding its utility across diverse domains.
It is published in Advanced Optical Materials.
這是首個能夠將自旋角動量以方向非對稱的方式轉換成任意的軌道角動量的雅努斯超穎介面。以二氧化鈦的超穎原子使其能在可見光範圍內運作。這些超穎原子還提供局部旋轉、全域旋轉與寬度控制，在單層設計中實現多功能性，超越了以往以空間多工或垂直堆疊的方法。
雅努斯超穎介面具備基於入射光方向的多樣化光操控功能，其應用範圍涵蓋從微波到中紅外光譜。然而，先前的設計常需依賴空間多工或垂直堆疊，導致製程複雜化。此外，金屬雅努斯超穎介面在可見光波段因材料特性而遭受顯著的歐姆損耗。在本研究中，實驗展示了一種單層以二氧化鈦實現的超穎介面，具備任意偏振控制功能，並展現出在自旋角動量和軌道角動量上的方向不對稱性。我們提出了一種專為雅努斯超穎介面量身定制的新的瓊斯矩陣公式，能有效生成兩種不對稱的高純度的光學渦漩，這些狀態依賴於 532 nm 波長下的入射光方向。此項創新促進了微型化且多功能的相位操控，並在未來的雷射和光合成器等應用中展現出廣泛的潛力，進而擴大其在多個領域中的應用範圍。
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