Investigation of symmetrical long-range surface plasmon resonance structure using induced transmission model

Symmetrical long-range surface plasmon resonance (Symm-LRSPR) is realized through the structure of "Prism/UpperDML/Metal/LowerDML/Analyte", showing sensitivity and penetration depth comparable to LRSPR. In this paper, simulation, and experiment are done on the penetration depth and sensitivity performance of this structure under different configurations of UpperDML/LowerDML layers. It is found that using medium and high refractive index materials for the UpperDML and LowerDML layer can achieve sensitivity performance similar to that of the Teflon/Cytop-based LRSPR. The performance of this structure is also very sensitive to the thickness of the LowerDML layer. Furthermore, the induced transmission model is introduced to explain the experimental phenomena and design results, and the results of the admittance diagram prove to be in good agreement with the experimental results. Our work shows that by adjusting the medium refractive index and the thickness of the LowerDML layer of this structure, we can achieve high-performance SPR at almost any refractive index of DML layer. Our findings significantly broaden the range of the DML materials that can be effectively used in the Symm-LRSPR structure.