Sharma Dushyant K, Pathak Surya K
Opt Express. 2016 Dec 26;24(26):29521-29536. doi: 10.1364/OE.24.029521.
In this study, we report slow wave propagation characteristics of an extremely anisotropic metamaterial loaded helical guide (EAMLHG). An analytical expression has been theoretically derived and numerically computed to get exact solutions of all possible guided modes of propagation. Anisotropy is defined in terms of positive longitudinal permittivity (ϵz > 0) and negatives transverse permittivity value (ϵt < 0). The waveguide supports hybrid (HE) mode propagation and possesses characteristics of backward wave (BW) mode, forward wave (FW) mode, zero-group velocity and mode-degeneracy. The large value of effective index of BW mode and mode-degeneracy mechanism leads to slowing and trapping of electromagnetic (EM) wave. Closed-form guided mode energy propagation expressions has been also derived and computed which exhibits zero power flow at mode degeneracy point. A comparative study is also carried out between extremely anisotropic metamaterial helical waveguide (EAMLHG) and conventional extremely anisotropic metamaterial cylindrical guide (EAMCG), which reveals enhanced slow wave behaviour. Engineering feasible design and analysis is also presented by combining alternate disks of silver and glass as an extremely anisotropic medium which exhibits lossy and dispersive properties. This type of waveguide can find applications as a filter, phase shifter, and delay lines in microwave to THz applications and, as an optical buffer in optoelectronics applications.
在本研究中，我们报告了一种极各向异性超材料加载螺旋波导（EAMLHG）的慢波传播特性。通过理论推导和数值计算得出了一个解析表达式，以获得所有可能导模传播的精确解。各向异性是根据正的纵向介电常数（ϵz > 0）和负的横向介电常数（ϵt < 0）来定义的。该波导支持混合（HE）模传播，并具有反向波（BW）模、正向波（FW）模、零群速度和模式简并的特性。BW模的有效折射率的大值和模式简并机制导致了电磁波的慢化和俘获。还推导并计算了封闭形式的导模能量传播表达式，该表达式在模式简并点处呈现零功率流。还对极各向异性超材料螺旋波导（EAMLHG）和传统的极各向异性超材料圆柱波导（EAMCG）进行了比较研究，结果表明慢波行为得到了增强。通过将银和玻璃的交替圆盘组合作为一种具有损耗和色散特性的极各向异性介质，还给出了工程上可行的设计和分析。这种类型的波导可作为滤波器、移相器和延迟线应用于微波到太赫兹应用中，以及作为光电子应用中的光缓冲器。
