High-efficiency spot size converter for photonic crystal fiber-to-waveguide using composite waveguide structures - Li, Haoyu; Li, Baoshuai; Zhuang, Xingang; Chen, Lingyun; Wu, Bin; Zhao, Luo; Zhu, Xingbang; Gao, Yesheng; Wu, Hengkui (Frontiers in Physics, 2024)