Unravelling energy transport in plasmon waveguides using dual-probe near-field optical microscopy: A feasibility study

几十年来，在计算机芯片上实现从纯电子结构到光子结构的信号传输一直是IT和电信行业的梦想。光可以以更快的速度和高度并行的方式传输信息；因此，光子信号分布将使我们能够克服现代多核计算机芯片进一步提高处理速度的主要障碍——互连瓶颈和带宽瓶颈。很有希望的是，近年来已经开发出一种潜在的纳米级几何形状的光引导技术：所谓的等离子体波导，微小的金属结构，如电线，切割成金属片的凹槽，或金属颗粒链，它可以将光以表面波的形式限制在金属界面上。至关重要的是，这些表面波仅在纳米尺度上延伸，远离金属，因此为紧密集成的光子（等离子体）电路开辟了一条道路。然而，主要的问题是金属结构在光学和近红外频率上具有固有的损耗。在我们的提案中，我们希望使用一种新颖的方法来确定等离子体波导最有前途的几何形状：使用两个微小的，独立移动的纳米级探针直接在波导的近场区域进行激发和收集，基本上是在纳米级环境本身。通过这种方式，我们可以以前所未有的细节研究能量转移的过程，以及局部化和损失之间的权衡。原则上，激发和收集都可以发生在直径仅为50纳米的区域上——比透镜和传统显微镜好10倍。到目前为止，所有在这个尺度上访问光场的方法都只使用了一个探头，因此限制了激发或探测的分辨率。如果我们成功地为这种双探针近场光学显微镜开发出一种工作方法，它将为纳米光子研究开辟一个全新的领域，并为纳米世界的功能操纵铺平道路，因为我们不仅有一个，而且有两个纳米尺度的手臂。

The switch from a purely electronic to a photonic architecture for distributing signals on a computer chip has been a visionary dream of the IT and telecommunications industry for decades. Light can transport information both faster and in highly parallelized fashion; therefore photonic signal distribution would enable us to overcome the main obstacles towards further increases in processing speed of modern, multiple-core computer chips - the interconnect bottle-neck, and the bandwidth bottle-neck. Promisingly, a potential technology for the guiding of light in nanoscale geometries has been developed in recent years: so called plasmon waveguides, tiny metallic structures such as wires, grooves cut into a metal sheet, or chains of metal particles, which can confine light to metallic interfaces in the form of a surface waves. Crucially, these surface waves extend only over nanoscale dimensions away from the metal, hence opening up an avenue towards tightly integrated photonic (plasmonic) circuits. The main problem however is that metallic structures are inherently lossy at optical and near-infrared frequencies. In our proposal, we want to identiy the most promising geometry for plasmon waveguides using a novel approach: the use of two tiny, independently movalbe nanoscale probes for exciation and collection directly in the near-field zone of the waveguide, essentially in the nanoscale environment itself. This way, we can investigate the process of energy transfer, and the trade-off between localization and loss, in unprecedented detail. In principle, both excitation and collection can occur over an area with a diameter on the order of only 50 nanometres - a factor ten better than with lenses and conventional microscopes. Thus far, all approaches to access light fields on this scale have employed one probe only, limiting therefore either the resolution in excitation, or in detection. If we succeed in developing a working methodology for this dual-probe near-field optical microscopy, it would open up a whole new landscape for nanophotonic investigations, and pave the way towards functional manipulation of the nanoworld by giving us not only one but two nanoscale arms .