Single-step-etched ultra-compact metamaterial grating coupler enabled by a hierarchical inverse design approach

作     者：Qiao Wang Ruiqi Luo Nan Liu Maojing Hou Bo Xiong Guandong Liu Wei Ma 

作者机构：Intelligent Network Research InstituteZhejiang LabHangzhou 311100China State Key Laboratory of Modern Optical InstrumentationCollege of Information Science and Electronic EngineeringZhejiang UniversityHangzhou 310027China 

出 版 物：《Science China(Physics,Mechanics & Astronomy)》 (中国科学：物理学、力学、天文学（英文版）)

年 卷 期：2024年第67卷第2期

页      面：119-126页

核心收录：

学科分类：080903[工学-微电子学与固体电子学] 070207[理学-光学] 07[理学] 0809[工学-电子科学与技术（可授工学、理学学位）] 08[工学] 0804[工学-仪器科学与技术] 0701[理学-数学] 0702[理学-物理学] 

基　　金：supported by the National Key Research and Development Program of China(Grant No.2021YFA1401200) the National Natural Science Foundation of China(Grant Nos.62322511,62105285,and 62275230). 

主　　题：waveguide hierarchical inverse 

摘      要：With the concept of metamaterials introduced into integrated photonics,subwavelength structures have gained popularity for their ability to create devices with ultra-compact size,high performance,and versatile functionalities.However,traditional metamaterial design methods are usually based on empirical templates and physical approximations,lacking the ability to design free-form metamaterial structures and optimize entire devices globally.In this work,we propose a hierarchical inverse design approach that combines a conventional effective refractive index based metamaterial structures design with a follow-up global topology optimization.The empirical metamaterial grating coupler design based on effective refractive index engineering faces inaccurate index extraction and insufficient approximation of wavevector matching conditions,which deteriorates coupling efficiency,especially for fully-etched devices with the decreased tapering region.Fortunately,a subsequent overall topology optimization step can well compensate for the negative effect of the shrinking device footprint to increase the efficiency of the metamaterial grating coupler.We demonstrate a 23μm×10μm ultra-compact metamaterial grating coupler with single-stepetched to couple light between a fiber and a 500 nm single-mode silicon waveguide in the O-band.Experimental measurement shows an insertion loss of 3.17 dB and a 3 dB bandwidth of 77 nm,making it the smallest footprint device ever reported.