Freeform Metasurface-Assisted Waveguide Coupler for Guided Wave Polarization Manipulation and Spin–Orbit Angular Momentum Conversion

Authors:
raw_author_name: Mingfeng Xu
raw_affiliation_string: National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu 610209, China; Research Center on Vector Optical Fields, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China; School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
raw_author_name: Mingbo Pu
raw_affiliation_string: National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu 610209, China; Research Center on Vector Optical Fields, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China; School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
raw_author_name: Yuhan Zheng
raw_affiliation_string: National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu 610209, China; Research Center on Vector Optical Fields, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China; School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
raw_author_name: Yinghui Guo
raw_affiliation_string: National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu 610209, China; Research Center on Vector Optical Fields, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China; School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
raw_author_name: Fei Zhang
raw_affiliation_string: National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu 610209, China; Research Center on Vector Optical Fields, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China; State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
raw_author_name: Nan Chi
raw_affiliation_string: Department of Communication Science and Engineering, Fudan University, Shanghai 200438, China
raw_author_name: Xiangang Luo
raw_affiliation_string: National Key Laboratory of Optical Field Manipulation Science and Technology, Chinese Academy of Sciences, Chengdu 610209, China; School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China

Abstract: Metasurface integrated waveguide couplers provide a promising pathway toward advanced manipulation of free-space light for guided wave coupling, such as polarization routing, mode-selective coupling, and wavelength (de)multiplexing. However, it is a great challenge to manipulate the guided wave polarization state to be completely decoupled from the polarization of incident light. Here, an adjoint-based topology optimization method is employed to inversely design a freeform metasurface for unidirectionally coupling free-space light into customized waveguide mode, with the capabilities of polarization manipulation and guided mode selection. An arbitrary transverse magnetic or transverse electric eigenmode can be unidirectionally excited for any incident polarization state conditions, with the maximum polarization-rotated mode purity and unidirectional coupling efficiency approaching 90.97 and 43%, respectively. Furthermore, by using multiobjective topology optimization, a meta-waveguide coupler with dual functions of generating polarization-controllable hybrid mode and realizing reconfigurable spin–orbit angular momentum conversion is inversely designed, leading to the increase of a mode (de)multiplexer channel number. Our work provides an effective strategy for multifunctional integrated on-chip devices and may have potential applications in optical communication, integrated optics, and quantum optics.