Sensitivity Enhancement of Modified D-Shaped Microchannel PCF-Based Surface Plasmon Resonance Sensor

High FOM PCF-SPR refractive index sensor based on MgF2-Au double-layer films

A simple twin-core D-shape photonic crystal fiber sensor based on surface plasmon resonance (SPR) is designed for the measurement of refractive indices (RI). The twin-core D-shape structure enhances the SPR effect, and the M g F 2-Au dual-layer film narrows the linewidth in the loss spectrum, consequently improving both the sensitivity and figure of merit (FOM). The properties of the sensor are analyzed by the finite element method. In the RI range of 1.32-1.42, the maximum wavelength sensitivity, FOM, and resolution are 62,000 nm/RIU, 1281R I U -1, and 1.61×10-6, respectively.

Plasmonic Perfect Absorber Utilizing Polyhexamethylene Biguanide Polymer for Carbon Dioxide Gas Sensing Application

In this paper a perfect absorber with a photonic crystal cavity (PhC-cavity) is numerically investigated for carbon dioxide (CO₂) gas sensing application. Metallic structures in the form of silver are introduced for harnessing plasmonic effects to achieve perfect absorption. The sensor comprises a PhC-cavity, silver (Ag) stripes, and a host functional material-Polyhexamethylene biguanide polymer-deposited on the surface of the sensor. The PhC-cavity is implemented within the middle of the cell, helping to penetrate the EM waves into the sublayers of the structure. Therefore, corresponding to the concentration of the CO₂ gas, as it increases, the refractive index of the host material decreases, causing a blue shift in the resonant wavelength and vice versa of the device. The sensor is used for the detection of 0-524 parts per million (ppm) concentration of the CO₂ gas, with a maximum sensitivity of 17.32 pm (pico meter)/ppm achieved for a concentration of 366 ppm with a figure of merit (FOM) of 2.9 RIU^-1. The four-layer device presents a straightforward and compact design that can be adopted in various sensing applications by using suitable host functional materials.

Cu2+-imprinted optical fiber SPR sensor for intelligent recognition

An optical fiber surface plasma resonance (SPR) sensor with MMF-TCF-MMF structure was designed to realize intelligent recognition of copper ions (Cu²⁺), and the selective adsorption sensitization was achieved by plating a layer of Cu²⁺-imprinted film on the surface of gold film excitation layer. Combining the principle of optical fiber interference and SPR, the proposed sensor realized the detection of the copper ions concentration through measuring the refractive index changes caused by ions adsorption on imprinted film. The Cu²⁺-imprinted optical fiber SPR sensor can realize the intelligent recognition and detection of copper ions in the complex environment and exhibits a detection sensitivity of -10.05 pm/ppm. The proposed sensor has tremendous development potential in practical application, and provides new ideas for the field of metal ions detection.

Detection of kerosene adulteration in automobile fuel by a low-loss surface plasmon resonance (SPR) chemical sensor

A surface plasmon resonance (SPR) chemical sensor with gold as the sensitive material has been designed to detect the adulteration of petrol by kerosene. Samples of petrol adulterated with kerosene were prepared in different ratios by volume (v/v). Kerosene concentrations ranging from 0% to 80% can be detected by monitoring the optical spectra, and the properties of the sensor were analyzed using the COMSOL Multiphysics software. The sensor shows a high spectral sensitivity of 7117 nm per RIU and a sensing resolution of 1.4 × 10^-4 RIU. The excellent sensing properties and a low confinement loss of 5.4 dB cm^-1 render the sensor competitive in SPR sensing applications.

Sensitivity Enhanced Refractive Index Fiber Sensor Based on Long-Range Surface Plasmon Resonance in SiO2-Au-TiO2 Heterostructure

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.

Near-infrared long-range surface plasmon resonance in a D-shaped honeycomb microstructured optical fiber coated with Au film

Long-range surface plasmon resonances (LRSPRs) are featured with longer propagation and deeper penetration, compared with conventional surface plasmon resonances (SPRs). Thus, LRSPR-based fiber sensors are considered to have great potential for highly sensitive detection in chemistry or biomedicine areas. Here, we propose and demonstrate a near-infrared LRSPR sensor based on a D-shaped honeycomb microstructured optical fiber (MOF) directly coated with gold film. Although there is no additional heterogeneous buffer layer, the optical field of the long-range surface plasmon polariton (LRSPP) mode penetrates strongly into the analyte region. Thus the effective refractive index of the LRSPP mode depends highly on the analyte's material refractive index and an abnormal dispersion relationship between the LRSPP mode and MOF's y-polarized core mode is observed. The mechanism of the LRSPR excitation in the coupling zone is attributed to an avoided crossing effect between these two modes. It also results in the generation of a narrow-bandwidth peak in the loss spectrum of the core mode. Further discussion shows that the resonance wavelength is mainly determined by the core size that is contributed by the MOF's cladding pitch, silica-web thickness and planar-layer-silica thickness together. It indicates that the operation wavelength of the proposed LRSPR device can be flexibly tuned in a broadband wavelength range, even longer than 2 µm, through appropriately designing the MOF's structural parameters. Finally, the proposed LRSPR sensor shows the highest wavelength sensitivity of 14700 nm/RIU and highest figure of merit of 475 RIU^-1 for the analyte refractive index range from 1.33 to 1.39.

Highly Sensitive Twin Resonance Coupling Refractive Index Sensor Based on Gold- and MgF2-Coated Nano Metal Films

A plasmonic material-coated circular-shaped photonic crystal fiber (C-PCF) sensor based on surface plasmon resonance (SPR) is proposed to explore the optical guiding performance of the refractive index (RI) sensing at 1.7–3.7 μm. A twin resonance coupling profile is observed by selectively infiltrating liquid using finite element method (FEM). A nano-ring gold layer with a magnesium fluoride (MgF2) coating and fused silica are used as plasmonic and base material, respectively, that help to achieve maximum sensing performance. RI analytes are highly sensitive to SPR and are injected into the outmost air holes of the cladding. The highest sensitivity of 27,958.49 nm/RIU, birefringence of 3.9 × 10−4, resolution of 3.70094 × 10−5 RIU, and transmittance dip of −34 dB are achieved. The proposed work is a purely numerical simulation with proper optimization. The value of optimization has been referred to with an experimental tolerance value, but at the same time it has been ensured that it is not fabricated and tested. In summary, the explored C-PCF can widely be eligible for RI-based sensing applications for its excellent performance, which makes it a solid candidate for next generation biosensing applications.