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

Abstract

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 <inline-formula><tex-math id="M302">\begin{document}$3.3\;{\text{μ}}{\rm{m}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181664_M302.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181664_M302.png"/></alternatives></inline-formula> 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.