一种分析楔形光纤的等效矩形近似-阶梯串联法

楔形光纤(WSF)是实现平面光波光路芯片入出端口与光纤高效连接的核心部件. 采用数值模拟方法分析其中光波传输演化过程，是优化设计光子器件耦合结构的重要基础. 提出基于等效矩形近似的三维阶梯串联法(ERA-SCM)，将楔端沿传输方向细分，引入矩形波导近似，给出了细分后各段近似矩形波导的等效折射率；在此基础上，建立了阶梯串联法分析模型，分级给出WSF中光波传输过程与模场演变. 数值分析结果表明，ERA-SCM比有限差分束传播法(FD-BPM)能够更精确地分析非对称光纤和波导结构，描述其中光模场的演化. WSF出射光场实测结果表明，ERA-SCM数值模拟结果与实验结果的误差为1.9%，而FD-BPM的误差为4.5%. ERA-SCM是分析非对称光波导光波传输与模场演变的有效方法. 关键词： 平面光波光路 楔形光纤 等效矩形近似 阶梯串联法

Equivalent rectangle approximation-staircase concatenation method for wedge shaped fiber

Wedge shaped fiber (WSF) is the key component to acquire high coupling efficiency between input/output ports of planar lightwave circuit chips and fiber arrays. It is very important to analyze the mode spot and the mode field evolution of the lightwave propagating in WSF using numerical simulation tools. A three_dimensional equivalent rectangle approximation-staircase concatenation method (ERA-SCM) is proposed to fractionize the wedged tip of WSF along the propagating direction and introduce rectangular waveguide approximation so that effective index of the segmentations is obtained and SCM analysis model is established. Lightwave propagation and mode field evolution is analyzed by ERA-SCM and compared with finite difference-beam propagation method (FD-BPM), showing that the former is more precise to solve mode field evolution for asymmetric fiber and waveguide structures. The measurement of the output optical spot verifies the ERA-SCM simulation error is within 1.9%, while that for FD-BPM method is 4.5%. Thus, ERA-SCM is an effective method for analyzing asymmetric fiber and waveguide structures.