Abstract
Long-range surface plasmon resonance (LRSPR), generated from a coupled plasmon polariton in a thin metal slab sandwiched by two dielectrics, has attracted more and more attention due to its merits, such as longer propagation and deeper penetration than conventional single-interface surface plasmon resonance. Many useful applications related to light–medium interaction have been demonstrated based on the LRSPR effect, especially in the sensing area. Here, we propose and demonstrate an LRSPR-based refractive index sensor by using a SiO2-Au-TiO2 heterostructure, in which a D-shaped honeycomb-microstructure optical fiber (MOF) is designed as the silica substrate and then deposited with a gold film and thin-layer titanium dioxide (TiO2). By using the full-vector finite-element method (FEM), this heterostructure is numerically investigated and demonstrated to excite LRSPR without a buffer layer, which is usually necessary in previous LRSPR devices. Through comprehensive discussion about the influence of structural parameters on the resonant wavelength, the excitation of the LRSPR in the proposed heterostructure is revealed to be highly related to the effective refractive index of MOF’s fundamental core mode, which is mainly determined by the MOF’s pitch, the thicknesses of the silica web and the planar-layer silica. Moreover, the thin-layer TiO2 plays an important role in significantly enhancing the resonance and the sensitivity to analyte’s refractive index as well, when it is coated on the top of the Au film rather than between the metal and waveguide. Finally, the proposed LRSPR sensor based on SiO2-Au-TiO2 heterostructure shows an ultra-high wavelength sensitivity of 20,100 nm/RIU and the corresponding minimum resolution is as low as 4.98×10−7 RIU. Thus, the proposed LRSPR device offers considerable potential for sensing applications in biomedical and biochemical areas.
Highlights
With the rapid development of multi-disciplinary science and technology in recent years, optical measurement methods and tools play significant roles in many areas, especially in chemistry, biology, medicine, and so on
We find that most of electric field of the long-range surface plasmon polariton (LRSPP) mode distributes in the analyte region
An Long-range surface plasmon resonance (LRSPR) sensor based on a SiO2-Au-TiO2 heterostructure on a D-shaped microstructure optical fiber (MOF) is proposed and numerically investigated
Summary
With the rapid development of multi-disciplinary science and technology in recent years, optical measurement methods and tools play significant roles in many areas, especially in chemistry, biology, medicine, and so on. The oscillations are very sensitive to any perturbation of the metal’s boundary, especially when the thickness of metal layer is as thin as several tens of nanometers It indicates that the SPR-based devices are intrinsically suitable for high-sensitivity detection [1,2,3,4]. An LRSPR refractive index sensor based on a SiO2-Au-TiO2 heterostructure is proposed and theoretically investigated. This heterostructure is composed of a D-shaped honeycomb-structure silica MOF coated with a thin-layer of Au and a TiO2 film sequentially. The corresponding minimum resolution is as low as 4.98 × 10−7 RIU
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