Detailed study of zigzag metal gratings

最近在光子学方面取得了许多令人兴奋的进展，表明金属结构可以在亚波长尺度上被图案化，从而显示出自然没有的新的电磁特性。虽然超材料这个术语最近才被创造出来来描述这些结构，但也许超材料最著名的例子是简单的衍射光栅。它最早是在18世纪末被研究出来的，在19世纪初发现了在光谱学中的应用，随后由于刻度引擎的发展，大量生产了反射光栅。从那时起，这一基本装置在整个电磁频谱中得到了广泛的应用。近年来，人们对亚波长尺度的金属透射栅的研究给予了相当大的关注，这在很大程度上是由于观察到了与波导和表面等离子体共振激发相关的增强传输现象。这里提出的之字形结构代表了一种全新的、迄今完全被忽视的超材料类型，对其的研究将汇集许多高度热门和活跃的研究领域。我们提出了一种计算机建模、制造和实验表征的方案，在可见光和毫米波长，非常适合两个博士生。第一个子项目将使用锯齿形光栅，为可见光辐射提供一种机制，使其与银膜和金膜上存在的表面模式(表面等离子激元)耦合。然而，在微波频率下，金属几乎是完美的导体，不存在束缚表面波。因此，我们必须依靠表面本身的微扰来诱导必要的边界条件，这样才能完全支持局域表面模。耦合到传统的表面等离子激元和微波等效子，将允许探索模在具有以前没有考虑过的新对称性的表面上的传播和色散，包括那些具有手性的表面。因此，我们希望观察到一种有趣的偏振响应，该表面能够将横向磁辐射和横向电辐射耦合成表面模，并可能从闪耀光栅中进行强烈的偏振转换。我们已经为电磁辐射与这种结构的相互作用提出了一种理论处理方法，因此，该项目的一个重要部分将是将这一理论发展成计算机代码。这不仅将允许与实验数据进行比较，而且还将有机会通过快速对与这些令人兴奋的结构相关的整个参数空间进行建模来发现最有趣的现象。我们还将利用商业数值模拟软件，该软件虽然速度慢得多，但将使研究人员能够从一开始就优化和研究结构。

There have been many recent and exciting advances in photonics demonstrating that metallic structures can be patterned on the subwavelength scale to exhibit novel electromagnetic properties not found naturally. While the term metamaterial has only recently been coined to describe these structures, perhaps the most famous example of a metamaterial is the simple diffraction grating. It was first studied in the late 18th century, finding use in spectroscopy in the early part of the nineteenth century, with mass production of reflection gratings following due to the development of ruling engines. Since then, this fundamental device has been employed extensively across the whole electromagnetic spectrum. In recent years considerable attention has been focused upon the study of metal transmission gratings structured on the subwavelength scale, this renewed interest largely being due to the observation of enhanced transmission phenomena associated with the excitation of waveguide and surface plasmon resonances. The zigzag structures proposed here present an entirely new, and as yet completely overlooked type of metamaterial, the study of which will draw together a number of highly topical and active research areas. We propose a programme of computer modelling, fabrication and experimental characterisation at both visible and millimeter wavelengths ideally suited to two PhD students. The first subproject will use zigzag gratings to provide a mechanism for visible radiation to couple to the surface modes (surface plasmons) that exist on silver and gold films. However, at microwave frequencies, where metals are almost perfect conductors, no bound surface waves exist. Therefore we must rely on the perturbation of the surface itself to induce the necessary boundary conditions so that localised surface modes can be supported at all. Coupling to both traditional surface plasmons, and the microwave equivalent, will allow for an exploration of the modes' propagation and dispersion on surfaces with novel symmetries not previously considered, including those with chiral properties. We therefore expect to observe an interesting polarisation response, with the surface able to couple both transverse magnetic and transverse electric radiation into surface modes, and potentially strong polarisation conversion from blazed gratings. We have already produced a theoretical treatment for the interaction of electromagnetic radiation with such a structure, and a vital part of the project will therefore be to develop this theory into a computer code. This will not only allow for a comparison to the experimental data, but also an opportunity to discover the most interesting phenomena by quickly modelling the whole of parameter space associated with these exciting structures. We will also utilise commercial numerical modelling software, which while much slower, will enable the researchers to optimise and study the structures from the outset.