Bao Jianfeng, Yang Dengcai, Chen Zhiyu, Zhang Jingyuan, Yang Feng
School of Physics and Optoelectronic Engineering, Institute of Laser Engineering, Beijing University of Technology, Beijing 100124, China.
Microwave Photonics Technology Laboratory, Chengdu 610036, China.
Micromachines (Basel). 2025 Jan 19;16(1):109. doi: 10.3390/mi16010109.
To enhance the end-face coupling efficiency of lithium niobate on insulator (LNOI) chips, in conjunction with current device fabrication processes, a stepped spot size converter (SSC) based on a special outer envelope profile has been proposed and investigated. This stepped SSC can reduce the coupling loss between the LNOI waveguide and a normal single-mode optical fiber. First, the output waveguide of a mode converter was proposed and simulated, in which the mode field had the biggest overlapping integral factor with a single-mode fiber (MDF ≈ 9.8 μm). Then, a stepped LNOI waveguide, the basic structure of the mode converter, with three kinds of outer envelope profile, was proposed and analyzed. Through analysis of the impacts of different envelope profiles on mode spot conversion efficiency, the relationship between envelope profile and propagation efficiency was obtained. Additionally, the rule of LNOI stair height variation tendency and the pattern of mode spot conversion efficiency for the multi-step mode spot converter in LNOI were obtained. Ultimately, a stepped SSC with a COS-shaped envelope curve was adopted. When this stepped SSC is coupled to single-mode fiber with a mode-field diameter of 9.8 μm, the coupling efficiency of the TE mode was 95.35% at the wavelength of 1550 nm.
为提高绝缘体上铌酸锂（LNOI）芯片的端面耦合效率，结合当前器件制造工艺，提出并研究了一种基于特殊外包层轮廓的阶梯式光斑尺寸转换器（SSC）。这种阶梯式SSC可降低LNOI波导与普通单模光纤之间的耦合损耗。首先，提出并模拟了模式转换器的输出波导，其中模式场与单模光纤具有最大的重叠积分因子（模场直径MDF≈9.8μm）。然后，提出并分析了作为模式转换器基本结构的具有三种外包层轮廓的阶梯式LNOI波导。通过分析不同包层轮廓对模式光斑转换效率的影响，得出了包层轮廓与传播效率之间的关系。此外，还得出了LNOI中多步模式光斑转换器的LNOI阶梯高度变化趋势规律和模式光斑转换效率模式。最终，采用了具有COS形包层曲线的阶梯式SSC。当这种阶梯式SSC与模场直径为9.8μm的单模光纤耦合时，在1550nm波长下TE模式的耦合效率为95.35%。
