磁光平面波导的单向传播特性

Properties of one-way propagation inthe magneto-optical planar waveguide

表面磁等离子体(surfacemagnetoplasmons,SMPs)是一种在电介质和偏置磁场作用下磁光材料界面处传播的近场电磁波.其独特的非互易传播特性引起了大量科研工作的关注,但在具体的波导结构设计上仍存在很多问题.本文研究了一种银-硅-磁光材料的3层平面波导结构,SMPs在磁光材料和硅的界面处传播,发现在特定的频率范围内,SMPs的基模及高阶模式均具有正向或反向的单向传播特性.分别计算了旋磁与旋电材料平面波导的色散方程,研究了硅层厚度与外加磁场对能带结构及SMPs单向传播区域的影响,发现无论是旋磁或旋电材料的结构,硅层厚度的增加使高阶模式使高阶模式出现在更低的频率位置,使单向传输带宽变小甚至消失,外加磁场的变大使磁光材料的能带结构频率增大的同时带隙中也引入了高阶模式.计算了2种磁光材料平面波导的正向和反向的单向传播带宽宽度,发现旋磁材料YIG的单向SMPs模式出现在GHz波段,最大单向带宽可达到2.45 GHz;旋电材料InSb的单向SMPs模式出现在THz波段,最大单向带宽达到3.9 THz.

Surface magnetoplasmons(SMPs)is a kind of near-field electromagnetic wave,which propagates at the interface of dielectricand magneto-optical material under the action of biased magnetic field.Because SMPs have excellent anti-interference and backscattering-immune properties,it has attracted wide attention of researchers in recent years,but there are still many problems in the design of waveguide structures.When electromagnetic waves propagate in magneto-optical materials,the faraday rotation effect makes the bias magnetic field and the magnetic field vector(or electrical displacement vector)not in the same direction,so the anti-angle elements of the second-order matrix of magnetic permeability(or dielectric constant)are asymmetric.This asymmetrymakes electromagnetic waves non-reciprocal when propagating in specific directions in magnetooptical materials,and can even achieve one-way propagation in a certain frequency range.In this paper,a structure of three-layerplanar waveguide with silver,silicon,and magneto-optical material is studied.SMPs propagate at the interface between silicon and magneto-optical materials.This work numerically calculates the dispersion relation of the waveguide and the band gap of the magneto-optical material.It is found that both the fundamental mode and the higher-order mode of SMPs have one-way propagation characteristics in forward or backward directionwithin a specific frequency range.The dispersion relation of the planar waveguides with gyromagnetic material andgyroelectricmaterial are calculated respectively.As a result,the thickness of silicon layer and the external magnetic field have significant influence on bulk mode and the one-way propagation region of SMPs.By increasing the thickness of the silicon layer or increasing the intensity of the magnetic field,the higher-order mode can appear at the lower frequency region,thus compressing the one-way propagation region or even losing the one-way propagation mode.The one-way propagation bandwidth of planar waveguideswith gyromagnetic material YIG and gyroelectric material InSbare calculated.Bycalculating the dispersion relation of the waveguide SMPs and the band gap of the magneto-optical material for each group of magnetic field and the thickness of Si,the colormap of YIG waveguideand InSbwaveguide under 400-20000 e magnetic field and 0.1-1 T magnetic field are obtained.As a result,the one-way mode of YIG waveguide appears in GHz band,and the maximum bandwidth for both forward and backward one-way propagation is2.45 GHz.While,the one-way mode of InSbwaveguide appears in THz band,the maximum one-way propagation bandwidth in forward and backward directions are 3.9 THz and 3.12 THz.The research results in this paper are of great significance for the design and fabrication of non-reciprocal waveguides with onewaypropagation characteristics.