Plasmon Drag Effect enabled by Metallic Nanowires inside Optical Fibers: fundamentals and optoelectronic aspects

探测不同频率的辐射是任何实际相关的光子系统的关键特征。一种很有前途的探测方案是光子阻力效应，目前正被用于中红外辐射的高速探测。这种效应是通过自由载流子吸收和将光子动量转移到电子，从而产生电流来实现的。由于高载流子浓度和高电导率，金属基本上是利用阻力效应的理想候选者。然而，金属的反射很强，导致电磁波和电子的重叠很少，因此阻力效应引起的电流可以忽略不计。解决这个问题的方法是表面等离子体激元(SPP)，它是束缚在金属/电介质界面上的极化子状态，场和金属有很大的重叠。因此，表面等离子体激元主要允许很强的动量转移，从而产生等离子体激元阻力效应。已经取得了非常有希望的初步结果，但到目前为止只进行了很少的效果验证调查，潜在的物理仍未被发现。缺乏硬数据的主要原因是平面等离子体薄膜的导电性差，激发方案不佳，以及光/金属相互作用长度不足。该项目的目标是从实验角度揭示PDE的基本物理，并评估其在等离子体光电探测方面的潜力。实验将依靠SPP在光纤内的纵向金属纳米线(NWS)上传播--一种解决上述问题的新型等离子体平台。原子核可能有几厘米长，直径只有几百纳米，因此将前所未有的长的光/金属相互作用长度与块状导电性结合在一起。NWS将电连接，允许直接测量PDE并分析其在各种条件下的特性。除了直接传输实验，柔性光纤处理将能够研究从常温到低温的偏振子效应，揭示声子和NW形态的影响。该光纤还通过发射短光脉冲为分析PDE的动态响应提供了理想的平台。在应用方面，本项目将评估PDE是否可以用于高效的等离子体、无半导体光电检测。这对于光纤来说尤其令人感兴趣，因为PDE代表了一种将高速检测方案集成到光纤中以达到完全单片光纤内探测器的独特方式。总之，本项目旨在基于光纤中的金属纳米波来研究PDE，目的有两个：(I)揭示PDE的潜在物理机制；(Ii)评估PDE在等离子体光电检测中的潜力。

Detecting radiation of various frequencies is key feature of any practically-relevant photonic system. One promising detection scheme is the Photon Drag Effect currently being employed for high-speed detection of mid-infrared radiation. The effect operates by free carrier absorption and a transfer of the photon momentum to electrons, leading to an electrical current. Metals are principally ideal candidates for exploiting the drag effect due to large carrier concentration and high electrical conductivity. However, metals strongly reflect, leading to only little overlap of electromagnetic wave and electrons and thus to negligibly small drag effect-induced currents.The solution to this problem are the surface plasmon polaritons (SPPs), which are polaritonic states bounded to metal/dielectric interfaces with a substantial overlap of field and metal. Hence SPPs principally allow a strong momentum transfer, giving rise to the plasmon drag effect (PDE). Very promising first results have been achieved, but only few prove-of-effect investigations have been conducted up to date, with the underlying physics remaining undiscovered. This lack of hard data mainly results from the poor electrical conductivity of planar plasmonic films, from suboptimal excitation schemes and from insufficient light/metal interaction lengths.The objectives of the project are to unlock the basic physics of the PDE from an experimental perspective and evaluate its potential for plasmonic optoelectronic detection. The experiments will rely on SPPs propagating on longitudinal metallic nanowires (NWs) inside optical fibers - a novel plasmonic platform solving all above-mentioned problems. The NWs can be several centimeters long with diameters of just several hundreds of nanometers, thus combining an unprecedentedly long light/metal interaction length with a bulk electrical conductivity. The NWs will be electrically connected, allowing to straightforwardly measuring the PDE and analyzing its characteristics under various conditions. Beside direct transmission experiments, the flexible fiber handling will enable investigating the PDE from ambient down to cryogenic temperatures, revealing the influence of phonons and NW-morphology. The fiber also provides the ideal platform for analyzing the dynamic response of the PDE by launching short optical pulses. In terms of application, this project will evaluate, if the PDE can be employed for efficient plasmonic, semiconductor-free optoelectronic detection. This is especially interesting for optical fibers, as the PDE represents a unique way to integrate a high-speed detection scheme into fibers for reaching a fully monolithic in-fiber detector.In summary, this project aims to investigate the PDE on the basis of metallic NWs in optical fibers with two objectives: (i) revealing the underlying physics of the PDE and (ii) evaluating the potential of the PDE in plasmonically optoelectronic detection.