Optimization focusing of surface plasmon polaritons with Fresnel phase zone pad on the silica-silver interface

Lam Yen Thi Nguyen^1*, Yu-Fang Chang¹, Yang-En Tseng¹, Hao-Min Chang¹, Chia-Chen Hsu¹, Jiunn-Yuan Lin¹, Hung-Chih Kan¹

¹Department of Physics, National Chung Cheng University, Chiayi, Taiwan

* Presenter:Lam Yen Thi Nguyen, email:thinguyen3108@gmail.com

Phase modulation with a dielectric Fresnel phase zone pad is proposed as a method for manipulating surface plasmon polaritons (SPPs), that could assist in the development of plasmonic integrated circuit. In this article, we demonstrate that utilizing the Fresnel phase zone pad (FPZP) structure with phase shift of π radians across consecutive zones enables the SPP to be focused into a high intensity spot, and subwavelength width at the interface of the silica and silver. The finite difference time domain (FDTD) simulation is use to investigate the characterization of the SPP focusing based on the diffraction with FPZP. The experimental result of the SPP focusing is examined with the up-conversion fluorescence microscopy. Altering the zone width and the focal length in the design of the FPZP structure allow us to further investigate in the optimization of FPZP structure has on the SPP focusing. we suggest a 4-level structure for the FPZP in order to enhance the intensity of the focus spot while simultaneously reducing the size of the spot because the addition of the new phase contribution interacts in such a manner as to focus the SPP flux in the first diffraction order and nearly totally suppress the others. Our findings demonstrate that the simulation and experiment of FPZP-assisted SPP focusing are qualitatively consistent with one another.

Keywords: surface plasmon polaritons, Fresnel phase zone pad, up-conversion fluorescent microscopy