Sensitivity Enhancement in D-Shaped Photonic Crystal Fiber Sensors: Gold Versus Silver Plasmonic Layers

Surface plasmon resonance (SPR) sensors have attracted great attention in recent years for various applications such as medical diagnosis and biochemical materials. Among SPR sensors, D-shaped structures based on photonic crystal fibers (PCFs) have shown very high performance and are easy to use. In this paper, a simple design of SPR sensors based on the D-shaped PCFs with the optimized geometrical parameters is proposed. Gold and silver are considered as plasmonic layers on the surface of the D-shaped PCF sensor. By performing multiple simulations using the finite-difference eigenmode (FDE) method, various values of gold and silver thicknesses are investigated to achieve the highest sensitivity and resolution. The results indicate that the highest sensitivity and resolution of 25,600 nm/RIU and 3.9x10-6\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$3.9\times {10}<^>{-6}$$\end{document} are achieved respectively for a gold thickness of 44 nm at the analyte refractive index (RI) of 1.41. Meanwhile, for an analyte RI range of 1.29 to 1.40, silver demonstrates greater sensitivity than gold in the same range. The proposed sensor with superior characteristics compared with other SPR sensors can be considered as a very good candidate for RI measurement with high sensitivity, linearity, and resolution.