银纳米线表面等离激元波导的能量损耗

金属纳米结构的表面等离激元可以突破光学衍射极限,为光子器件的微型化和集成光学芯片的实现奠定基础.基于表面等离激元的各种基本光学元件已经研制出来.然而,由于金属结构的固有欧姆损耗以及向衬底的辐射损耗等,表面等离激元的传输能量损耗较大,极大地制约了其在纳米光子器件和回路中的应用.研究能量损耗的影响因素以及如何有效降低能量损耗对未来光子器件的实际应用具有重要意义.本文从纳米线表面等离激元的基本模式出发,介绍了它在不同条件下的场分布和传输特性,在此基础上着重讨论纳米线表面等离激元传输损耗的影响因素和测量方法以及目前常用的降低传输损耗的思路.最后给出总结以及如何进一步降低能量损耗方法的展望.表面等离激元能量损耗的相关研究对于纳米光子器件的设计和集成光子回路的构建有着重要作用.

Energy loss of surface plasmon polaritons on Ag nanowire waveguide

Metal nanostructures can support surface plasmon polaritons (SPPs) propagating beyond diffraction limit, which enables the miniaturizing of optical devices and the integrating of on-chip photonic and electronic circuits. Various surface plasmon based optical components have already been developed such as plasmonic routers, detectors, logic gates, etc. However, the high energy losses associated with SPPs' propagation have largely hampered their applications in nanophotonic devices and circuits. Developing the methods of effectively reducing energy loss is significant in this field. In this review, we mainly focus on the energy losses when SPPs propagate in Ag nanowires (NWs). Researches on energy loss mechanism, measurement approaches and methods of reducing energy loss have been reviewed. Owing to their good morphology and high crystallinity as well as low loss in visible spectrum, chemically synthesized Ag NWs are a promising candidate for plasmonic waveguides. The energy losses mainly arise from inherent Ohmic damping, scattering process, leaky radiation and absorption of substrate. These processes can be influenced by excitation wavelength, the geometry of NW and the dielectric environment, especially the effect of substrate, which is discussed in the review. Longer excitation wavelength and larger NW diameter can induce decreased mode confinements and smaller Ohmic loss. The experimental methods to measure the energy loss have been summarized. Researches on reducing energy loss have been reviewed including applying dielectric layer or graphene between NW and substrate, replacing commonly used substrate with a dielectric multilayer substrate, introducing gain materials, and forming hybrid waveguides by using the semiconductor or dielectric NW. Specifically, the leaky radiation can be prevented when an appropriate dielectric layer is placed between NW and substrate, and the mode confinement can be reduced which leads to decreased Ohmic loss. The gain materials can be used to compensate for the energy loss during propagation. Compared with metal waveguides, semiconductor or dielectric NWs suffer lower energy losses while decreased field confinement. Then the hybrid waveguides constructed by metal and dielectric NWs can combine their advantages, which possesses reduced propagation loss. In addition, the plasmon modes in NWs in a homogeneous medium and a substrate are briefly discussed respectively, followed by the introduction to fundamental properties of SPPs propagation. Finally, perspectives of the future development of reducing energy loss are given. The researches on reducing energy loss are crucial for designing and fabricating the nanophotonic devices and integrated optical circuits.