Zhou Nan, Zheng Shuang, Cao Xiaoping, Zhao Yifan, Gao Shengqian, Zhu Yuntao, He Mingbo, Cai Xinlun, Wang Jian
Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074 Hubei, China.
State Key Laboratory of Optoelectronic Materials and Technologies and School of Physics and Engineering, Sun Yatsen University, Guangzhou 510275, China.
Sci Adv. 2019 May 31;5(5):eaau9593. doi: 10.1126/sciadv.aau9593. eCollection 2019 May.
Orbital angular momentum (OAM), one fundamental property of light, has been of great interest over the past decades. An ideal OAM generator, fully compatible with existing physical dimensions (wavelength and polarization) of light, would offer the distinct features of broadband, polarization diversity, and ultra-compact footprint. Here, we propose, design, fabricate, and demonstrate an ultra-compact chip-scale broadband polarization diversity OAM generator on a silicon platform with a 3.6 × 3.6 μm footprint. The silicon OAM chip is formed by introducing a subwavelength surface structure (superposed holographic fork gratings) on top of a silicon waveguide, coupling the in-plane waveguide mode to the out-plane free-space OAM mode. We demonstrate in theory and experiment the broadband generation of polarization diversity OAM modes (x-/y-polarized OAM/OAM) from 1500 to 1630 nm with high purity and efficiency. The demonstrations of an ultra-compact broadband polarization diversity OAM generator may open up new perspectives for OAM-assisted N-dimensional optical multiplexing communications/interconnects and high-dimensional quantum communication systems.
轨道角动量（OAM）是光的一种基本属性，在过去几十年中一直备受关注。一种与光现有的物理维度（波长和偏振）完全兼容的理想OAM发生器，将具有宽带、偏振多样性和超紧凑尺寸等显著特点。在此，我们提出、设计、制造并展示了一种超紧凑的芯片级宽带偏振多样性OAM发生器，该发生器基于硅平台，尺寸仅为3.6×3.6μm。硅OAM芯片是通过在硅波导顶部引入亚波长表面结构（叠加全息叉形光栅），将面内波导模式耦合到面外自由空间OAM模式而形成的。我们在理论和实验上均证明了在1500至1630nm范围内能够以高纯度和高效率宽带产生偏振多样性OAM模式（x/y偏振OAM/OAM）。超紧凑宽带偏振多样性OAM发生器的展示可能会为OAM辅助的N维光复用通信/互连以及高维量子通信系统开辟新的前景。
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