横电磁模导行光纤中电磁波的传播

Traditional waveguide theory seldom discusses the transverse electromagnetic (TEM) modes in dielectric waveguides. This is understandable. For a waveguide composed of two isotropic media, the guidance of TEM modes requires that one of the media is negatively refractive. Although, the concept of negative refraction was already proposed by Veselago in 1968, negatively refractive media are not naturally exist, and was artificially fabricated only until the year of 2000. Recent theoretical studies show that under certain condition of electromagnetic parameters, negatively refractive fibers possess the solution of TEM modes, and the distribution of modal fields can be arbitrary. The property of arbitrariness of modal fields is not only very interesting in physics, but also may provide a novel space-division-multiplexing mechanism in applications. The fiber guiding TEM modes is the only known waveguide structure that possesses the property of arbitrariness of modal fields. For this type of unique optical fibers, up to now, only modal analysis has been performed, and the unsolved physical problems include the steady-state analysis with excitation source and transient analysis. We would investigate the above two problems by analytical calculation and numerical simulation, illustrating the physical picture of the propagation of electromagnetic waves in the fibers guiding TEM modes, and evaluating the possibility of applying such exotic fibers in space-division-multiplexing.

传统波导理论甚少论及介质波导中的横电磁模。这是可以理解的。对于由两种各向同性介质构成的波导，导行横电磁模要求其中一种介质是负折射的。尽管负折射的概念在1968年即由Veselago提出，但负折射材料并不天然存在，直到2000年才首次由人工制造出。近期的理论研究表明，在特定电磁参数条件下，负折射光纤具有横电磁模解，且模场分布具有任意性。模场分布任意的特性不仅在物理上极为有趣，同时有可能在应用上提供一种新颖的空分复用机制。横电磁模导行光纤是已知的唯一具有模场任意性的波导结构。对于这类独特光纤，目前仅进行了模式分析，亟待解决的物理问题包括带有激励源的稳态分析和瞬态分析。本项目将对上述两个问题做解析计算和数值模拟，以期阐明横电磁模导行光纤中电磁波传播的物理图象，并评估这种奇异光纤应用于空分复用的可能性。

横电磁模导行光纤是一类特殊的负折射光纤，具有模场任意性的新奇性质，有望用于实现高密度、低能耗的光纤通信空分复用。模场任意性意味着最终的模式图案完全由激励源条件决定。在之前的研究中，研究者只是从模式理论上预言了横电磁模导行光纤的模场任意性，而未进行带有激励源的分析。.本项研究首先利用时域有限差分方法，进行了面源激励下横电磁模导行光纤的频域分析和时域分析，证实了光纤中可以存在不具备旋转对称性的模式，为模场任意性提供了直接证据。另外，研究发现模场任意性是稳定的，在小的结构参数偏离下，模场图案亦变化很小。在此研究结果的支持之下，我们有理由继续深入探究横电磁模导行光纤的实现问题，及通信相关的信号编码及模式激发问题。.横电磁模导行光纤最有望在手性版本中实现，我们开展了手性波导模式求解器、手性材料和手性波导制备等方面的研究。基于浸没界面方法，开发了适用于手性多层光纤和手性多层平面波导的高效模式求解器，并验证了其通用性及计算性能。基于嵌段共聚物自组装，研究了如何制备期望的手性纳米结构和控制缺陷结构，为手性负折射光纤的制备提供了一种新颖的思路。