金属-光折变材料复合全息结构对表面等离激元的波前调控

表面等离激元(surface plasmon polaritons, SPPs)控制具有重要意义.表面电磁波全息法是在金属表面设计能有效控制SPP传输的凹槽阵列结构.本文提出一种新的SPP传输的控制方法,利用金属-光折变材料复合全息结构控制SPP传播.在金属表面覆盖一层光折变材料,两束SPP波在光折变材料内干涉生成全息结构,利用此全息结构能够控制SPP的传播.通过时域有限差分法模拟验证,结果显示,通过金属-光折变材料复合全息结构可以有效地控制SPP波束的传输,实现SPP平面波束的单点聚焦、两点聚焦,以及生成零阶和一阶高斯SPP波束.经过优化发现,光折变材料的最佳厚度为3.3μm,最佳折射率调制度为0.06.现有SPP控制器件主要是通过离子束刻蚀,而金属-光折变材料复合全息结构不需要刻蚀,从而扩展了SPP控制的器件的制作方法,为SPPs的全光控制提供了新的思路,使SPP全光控制成为可能,进一步实现了SPP全光开关等功能.

Surface plasmon polaritons' propagation controlled by metal-photorefractive material composite holographical structure

Control of surface plasmon polaritons' (SPPs') propagation is of great importance. The groove structure in metal surface, designed by the surface electromagnetic wave holography (SWH) method, can control the SPPs' propagation effectively. In the SWH method, all designed groove structures are etched in metal surface. The fabrication method is confined to the etching method, such as the focused ion beam lithography and electron beam lithography. And the designed structures cannot implement the real-time control of SPP propagation. We propose a new method to control SPPs' propagation through metal-photorefractive material composite holographical (MPRCH) structures. A photorefractive material film is coated on the metal surface, and the reference SPP wave interferes with the object SPP wave in the photorefractive material film. The interference intensity is recorded by the photorefractive material film, forming the MPRCH structure. The MPRCH structure is used to control the propagation of relatively weak SPP waves. The finite difference time domain method is used to verify the method. We simulate that a reconstructed SPP wave is incident into the structure region and interacts with the structure. The incident wave is reflected and scattered by the designed MPRCH structure. These reflected and scattered wave are propagated and superposed, forming the desired SPP wave on the metal surface. Simulation results show that the MPRCH structure can control SPPs' propagation effectively and realize the functions such as SPP wave aside single-point focusing, two-point focusing, generating zero-order and first-order Gaussian SPP beams. It is found that the optimal thickness of the MPRCH film is \$3.3{\text{μ}}{\rm{m}}$\ and modulation amplitude of refractive index is 0.06. This method extends the SPP device fabrication methods, and gets rid of the etching method. Based on the investigation, the real-time controlling of SPP wave may be realized through the MPRCH structure. The study provides a new idea for realizing the all-optical control of SPP propagation, thus making it possible to implement the all-optical control of SPP and further switch.