Zhang Zan, Shan Xiaotao, Huang Beiju, Zhang Zanyun, Cheng Chuantong, Bai Bing, Gao Tianxi, Xu Xiaobo, Zhang Lin, Chen Hongda
School of Electronic and Control Engineering, Chang'an University, Xi'an 710064, China.
Chinese Academy of Sciences, Beijing 100083, China.
Materials (Basel). 2020 Jun 12;13(12):2681. doi: 10.3390/ma13122681.
In this work, a bidirectional grating coupler for perfectly vertical coupling is proposed. The coupling efficiency is enhanced using a silicon nitride (SiN) layer above a uniform grating. In the presence of SiN layer, the back-reflected optical power into the fiber is diminished and coupling into the waveguide is increased. Genetic algorithm (GA) is used to optimize the grating and SiN layer simultaneously. The optimal design obtained from GA shows that the average in-plane coupling efficiency is enhanced from about 57.5% (-2.5 dB) to 68.5% (-1.65 dB), meanwhile the average back-reflection in the C band is reduced from 17.6% (-7.5 dB) to 7.4% (-11.3 dB). With the help of a backside metal mirror, the average coupling efficiency and peak coupling efficiency are further increased to 87% (-0.6 dB) and 89.4% (-0.49 dB). The minimum feature size of the designed device is 266 nm, which makes our design easy to fabricate through 193 nm deep-UV lithography and lowers the fabrication cost. In addition, the coupler proposed here shows a wide-band character with a 1-dB bandwidth of 64 nm and 3-dB bandwidth of 96 nm. Such a grating coupler design can provide an efficient and cost-effective solution for vertical fiber-to-chip optical coupling of a Wavelength Division Multiplexing (WDM) application.
在这项工作中，提出了一种用于完美垂直耦合的双向光栅耦合器。通过在均匀光栅上方使用氮化硅（SiN）层来提高耦合效率。在存在SiN层的情况下，进入光纤的背向反射光功率减小，而进入波导的耦合增加。遗传算法（GA）用于同时优化光栅和SiN层。从GA获得的优化设计表明，面内平均耦合效率从约57.5%（-2.5 dB）提高到68.5%（-1.65 dB），同时C波段的平均背反射从17.6%（-7.5 dB）降低到7.4%（-11.3 dB）。借助背面金属镜，平均耦合效率和峰值耦合效率进一步提高到87%（-0.6 dB）和89.4%（-0.49 dB）。所设计器件的最小特征尺寸为266 nm，这使得我们的设计易于通过193 nm深紫外光刻制造，并降低了制造成本。此外，这里提出的耦合器具有宽带特性，1 dB带宽为64 nm，3 dB带宽为96 nm。这种光栅耦合器设计可为波分复用（WDM）应用的垂直光纤到芯片光耦合提供一种高效且经济高效的解决方案。
