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

从纯电子到光子架构的转换，用于在计算机芯片上分配信号，这是IT和电信行业几十年来的梦想。光可以更快地以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进一步提高现代多核计算机芯片处理速度的主要障碍-互连瓶颈和带宽瓶颈。有希望的是，近年来已经开发了一种用于在纳米级几何形状中引导光的潜在技术：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，其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远离金属，因此开辟了一条通往紧密集成光子（等离子体）电路的途径。然而，主要问题是金属结构在光学和近红外频率下固有地有损耗。在我们的提案中，我们希望使用一种新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，我们可以前所未有地详细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十倍。到目前为止，所有的方法来访问光场在这个规模上只采用了一个探头，因此限制了分辨率的激发，或在检测。如果我们成功地为这种双探针近场光学显微镜开发了一种工作方法，它将为纳米光子研究开辟一个全新的领域，并为我们提供不仅一个而是两个纳米级手臂，为功能操纵世界铺平道路。

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 .