Propagation Controlled Photonic Crystal Fiber-Based Plasmonic Sensor via Scaled-Down Approach

Light trapping capability is the key phenomena of the photonic crystal fiber (PCF) which paves the broad range of applications. In this work, we control the light-guiding direction of the proposed PCFs <italic>via</italic> scaled-down approach to enhance the coupling between core-guided mode and surface plasmon polariton (SPP) mode resulting in the increase of sensitivity. We introduce the scaled-down air-holes in the first and second rings of the proposed PCF which provides the light guiding capability through the desire scaled-down region. A chemically stable plasmonic material gold is used outside the PCF structure to facilitate the detection of unknown analyte externally. Finite element method is used for numerical investigations, and the sensor performance is investigated by following the wavelength and amplitude interrogation methods. The proposed sensor shows the maximum wavelength sensitivities of 30 000 and 22 000 nm/RIU, and the maximum amplitude sensitivities of 1212 RIU⁻¹ and 1506 RIU⁻¹ for <inline-formula> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula>- and <inline-formula> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula>-polarized modes, respectively in the analyte refractive index (RI) range of 1.33 to 1.39. It also shows high sensor wavelength resolution of <inline-formula> <tex-math notation="LaTeX">$3.33\times 10^{-6}$ </tex-math></inline-formula> RIU and <inline-formula> <tex-math notation="LaTeX">$4.54\times 10^{-6}$ </tex-math></inline-formula> RIU, and a figure of merit about 508 and 500 for <inline-formula> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula>- and <inline-formula> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula>-polarized modes, respectively. It should be noted that the proposed PCF SPR sensor shows the significant sensing response for both polarization modes, as a result it will provide more freedom in choosing light source during practical implementation. Furthermore, the finding results indicates the proposed sensor will be effective for the detection of organic chemicals, biomolecules, and medical diagnostics.