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<p>A fibre-based surface plasmon resonance (SPR) sensor architecture is numerically investigated for resolving near-unity refractive-index variations in a polymer-coated fibre geometry using angular modulation. The proposed structure employs a multilayer coating on the fibre sensing region consisting of Ag-Cr-(Bi<sub>2</sub>O<sub>3</sub>-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>)-VOC-sensitive polymer, enabling plasmon excitation under total internal reflection and interrogation through angular modulation. The Bi<sub>2</sub>O<sub>3</sub>-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> film layer provides a high refractive index and broad transparency, enabling strong field localisation. Finite-element simulations are used to analyse field confinement and evanescent penetration at representative angles, demonstrating enhanced interface-localised fields at lower angles, thereby increasing overlap with the polymer layer. The angular SPR response exhibits a sharp resonance near 44°, with limited wavelength-dependent drift across 630–636&#xa0;nm (43.86–43.95°), supporting a stable angular operating point; performance metrics in this band indicate favourable behaviour near ~ 634&#xa0;nm. To examine refractometric response in a gas-phase-relevant regime, the refractive index of the outer polymer layer is perturbed by small increments, and the resonance shift is extracted. For sensing RI ranging from 1.001 to 1.010, the resonance angle shifts monotonically from 43.8599° to 44.4031° (Δθres = 0.5432°), yielding an angular sensitivity of ~ 60°/RIU with only modest broadening of the linewidth. These results substantiate plasmonic angular modulation in a fibre-guided SPR geometry as an effective approach for resolving ultralow refractive-index variations relevant to gas-phase VOC sensing.</p>

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Numerical Investigation of a Polymer-coated Fiber SPR Platform for Near-unity Refractive Index Sensing Relevant to VOC Detection

  • 期刊论文

  • 发表日期：

    2026年4月1日

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  • Amrita Deepika V G,
  • Bibhatsu Kuiri,
  • Rittwick Mondal,
  • Soumyajyoti Kabi,
  • Gagan Anand

摘要

A fibre-based surface plasmon resonance (SPR) sensor architecture is numerically investigated for resolving near-unity refractive-index variations in a polymer-coated fibre geometry using angular modulation. The proposed structure employs a multilayer coating on the fibre sensing region consisting of Ag-Cr-(Bi2O3-Al2O3-SiO2)-VOC-sensitive polymer, enabling plasmon excitation under total internal reflection and interrogation through angular modulation. The Bi2O3-Al2O3-SiO2 film layer provides a high refractive index and broad transparency, enabling strong field localisation. Finite-element simulations are used to analyse field confinement and evanescent penetration at representative angles, demonstrating enhanced interface-localised fields at lower angles, thereby increasing overlap with the polymer layer. The angular SPR response exhibits a sharp resonance near 44°, with limited wavelength-dependent drift across 630–636 nm (43.86–43.95°), supporting a stable angular operating point; performance metrics in this band indicate favourable behaviour near ~ 634 nm. To examine refractometric response in a gas-phase-relevant regime, the refractive index of the outer polymer layer is perturbed by small increments, and the resonance shift is extracted. For sensing RI ranging from 1.001 to 1.010, the resonance angle shifts monotonically from 43.8599° to 44.4031° (Δθres = 0.5432°), yielding an angular sensitivity of ~ 60°/RIU with only modest broadening of the linewidth. These results substantiate plasmonic angular modulation in a fibre-guided SPR geometry as an effective approach for resolving ultralow refractive-index variations relevant to gas-phase VOC sensing.