梯形截面硅基水平多槽纳米线定向耦合器全矢量分析

FuU-vectorial analysis of the directional couplers in horizontal multiple-slotted silicon wires with trapezoidal cross-section

定向耦合器是构成各类光子器件的基础元件.本文采用一种基于电场分量的全矢量有限元法,分析由梯形截面硅基水平多槽纳米线构成的定向耦合器.给出了准TE与准TM偶、奇模有效折射率、耦合长度及模场分布,揭示了其模式的混合特性及模场分布特点.分析结果表明,准TE模与准TM模的耦合长度随波导间距的增大均呈指数增长,其中准TE模的耦合长度对波导侧壁倾角的变化敏感,而准TM模的耦合长度对槽厚及槽折射率的变化敏感.恰当选择结构与材料参数,可实现两偏振态下相同耦合长度,定向耦合器在偏振无关条件下工作.

Directional couplers are basic components for forming various kinds of photonic devices. In this paper, a directional coupler composed of two horizontal multiple-slotted waveguide structures with slanted sidewalls is characterized by using a full-vectorial finite element method in terms of the electric fields. The effective indexes of the even and the odd modes and the corresponding coupling lengths, both in quasi-TE and quasi-TM modes, are presented, where the strongly-hybrid nature of the guided-mode is effectively demonstrated. The results show that the coupling lengths in quasi-TE and quasi-TM modes exponentially increase with the increase of the gap between the coupled waveguides, where the value in quasi-TE mode is more sensitive to the variation of the angle of the sidewall, while the value in quasi-TM mode is more sensitive to variation of the height and the index of the slot. Properly choosing the structure and material parameters, polarization-independent directional couplers can be realized.