Li Ying, Lan Tian, Li Jing, Wang Zhiyong
Appl Opt. 2020 Aug 1;59(22):6694-6701. doi: 10.1364/AO.395897.
Edge-coupling on single-crystal thin-film lithium niobate on insulator (LNOI) was systematically studied in this paper. An inverse taper-shaped spot-size converter (SSC) to convert the mode field from the laser chip to a nanoscale LNOI waveguide was adopted to improve the coupling efficiency. Structure of the edge coupler was fully investigated and optimized by using the eigenmode expansion method. The single-mode conditions of the LNOI waveguide for three common communication bands were taken into consideration. Further, the length and tip width of the inverse taper, the cross-section dimensions of SiON waveguide, and the sidewall angle were investigated with respect to coupling efficiency. As a result, the maximum coupling efficiency from an edge coupler to laser chip can reach 54%, 48%, and 58% at 1550, 1310, and 850 nm in Z-cut LNOI for quasi-TM mode, respectively. This proposed work gives a better understanding of the function of the edge coupler based on LNOI material and provides an appropriate method for the design of an edge coupler with high efficiency, which could benefit the further application of high-density monolithic integrated optical components.
本文系统研究了绝缘体上的单晶薄膜铌酸锂（LNOI）上的边缘耦合。采用反向锥形光斑尺寸转换器（SSC）将激光芯片的模式场转换为纳米级LNOI波导，以提高耦合效率。利用本征模展开法对边缘耦合器的结构进行了全面研究和优化。考虑了LNOI波导在三个常用通信波段的单模条件。此外，研究了反向锥形的长度和尖端宽度、SiON波导的横截面尺寸以及侧壁角度对耦合效率的影响。结果表明，在Z切LNOI中，对于准TM模式，边缘耦合器到激光芯片在1550、1310和850nm处的最大耦合效率分别可达54%、48%和58%。这项工作有助于更好地理解基于LNOI材料的边缘耦合器的功能，并为高效边缘耦合器的设计提供了一种合适的方法，这将有利于高密度单片集成光学元件的进一步应用。
