We explore scattering effects as the physical origin of cross-polarization and higher-order modes in silicon photonic 2D grating couplers (GCs). A simplified analytical model is used to illustrate that in-plane scattering always takes place, independent of grating geometry and design coupling angle. Experimental investigations show furthermore that grating design parameters are especially related to the modal composition of both the target- and the cross-polarization. Scattering effects and the associated cross-polarization and higher-order modes are indicated as the main reason for the higher 2D GC insertion loss compared to standard 1D GCs. In addition, they can be responsible for a variable 2D GC spectrum shape, bandwidth and polarization dependent loss.

我们探索散射效应作为硅光子二维光栅耦合器 (GC) 中交叉极化和高阶模式的物理起源。简化的分析模型用于说明面内散射总是发生，与光栅几何形状和设计耦合角无关。实验研究进一步表明，光栅设计参数与目标极化和交叉极化的模态组成特别相关。散射效应和相关的交叉极化和高阶模式被认为是与标准 1D GC 相比更高的 2D GC 插入损耗的主要原因。此外，它们可能导致可变的 2D GC 光谱形状、带宽和偏振相关损耗。