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A highly sensitive and simple structure side-polished micro-structured fiber (MOF) refractive index (RI) sensor based on surface plasmon resonance is proposed and studied by the finite element method. The gold nanofilm used to stimulate plasmons is directly deposited on the inner wall of the open-loop channel of a MOF consisting of an arrangement of six cladding air-holes. The sample analyte is arranged on the outer surface of the optical fiber to improve the utilization rate of the sensor and reduce the tediousness of operation. Meanwhile, in order to increase the leakage intensity of evanescent field, three large air-holes were introduced near the fiber core. Research has shown that the proposed sensor can achieve sensing detection in the range of 1.19–1.37 RI. The maximum sensitivity in the x-polarized direction can reach 12,500 nm/RIU, and its corresponding resolution is 3.64 × 10–5 RIU. Moreover, it has a high linear response of 0.9944 within the RI detection range of 1.19–1.33. Obviously, the proposed sensor has a simple structure, wide RI detection range, and high sensitivity, which can make it widely used in biomedical and analytical chemistry. [ABSTRACT FROM AUTHOR]

A dual-polarized photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) was proposed for measuring the refractive indexes (RIs) of liquids. A gold film and a liquid analyte were successively wrapped around the outer surface of the PCF to stimulate the external SPR effect, which greatly reduced the manufacturing difficulties, compared to depositing the gold film and filling the inner air holes of the PCF with liquid analyte. The performance of the proposed PCF sensor was numerically investigated using the finite-element method. The results show that the proposed PCF sensor can realize dual-polarized detection in the RI range of 1.36–1.42. The x and y polarization (X-P and Y-P) core modes were coupled to the X-P second-order and Y-P first-order surface-plasmon polariton modes, respectively. As the the RI of the analyte increased, the wavelength sensitivity increased and, as a result, maximum values of 15 900 nm RIU−1 for X-P and 16 900 nm RIU−1 for Y-P were achieved. Correspondingly, we obtained a maximum amplitude sensitivity of 2026.05 RIU−1 for X-P and 2102.65 RIU−1 for Y-P. In addition, the fabrication tolerance of the proposed PCF was increased to ±0.4 μm, which made the proposed PCF a favorable candidate for the detection of liquids. [ABSTRACT FROM AUTHOR]

A fiber/Ag-Cu films surface plasmon resonance (SPR) refractive index (RI) sensor composed of multimode fiber-no-core-fiber-multimode fiber (MMF-NCF-MMF) structure is designed. The sensing region length and Cu film deposition time of sensor are gradually optimized by the control variable method, which finally achieves the improvement of sensor properties. We experimentally compared the sensing performance of the fiber/Ag film and fiber/Ag-Cu films sensor. Experimental results show that the fiber/Ag-Cu films sensor has good linearity (R-square = 0.993), and its sensitivity is as high as 3957 nm/RIU in the refractive index detection range of 1.3328–1.3853, which is 1109 nm/RIU higher than the sensitivity of a conventional fiber/Ag film sensor. The sensor presented in this paper adopts the structure with composite metal film, which outperforms the common single-layer metal film in chemical stability such as oxidation resistance and mechanical hardness. Meanwhile, the SPR sensor with MMF-NCF-MMF structure has the advantages of convenient manufacture and compact structure. In conclusion, it can bestow a unique advantage in the field of biological detection or chemical analysis. [ABSTRACT FROM AUTHOR]

• A novel SPR sensor based on D-shaped PCF with offset-core is proposed and demonstrated for the liquid RI measurement. • The structural design of the D-shaped fiber makes the placement of the liquid to be tested more convenient. • The SPR sensor with high sensitivity can be realized by introducing the offset-core. • Ultra-high wavelength sensitivity and amplitude sensitivity of 42,000 nm/RIU and 2204.49 RIU−1 are obtained. We propose a novel D-shaped offset-core photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) for the liquid refractive index (RI) measurement. The D-shaped structural design makes the placement of the liquid to be tested more convenient. The offset-core is designed to improve the sensitivity of the SPR sensor. The optical propagation characteristics of the proposed sensor were investigated by the finite element method (FEM). Numerical results show that more energy of the core mode transfers to the gold surface as the analyte RI increases. The wavelength sensitivity increases with the increase of RI, and the maximum wavelength sensitivity can reach to 42,000 nm/RIU. What's more, the maximum amplitude sensitivity is up to 2204.49 RIU−1. The proposed sensor shows excellent performances in terms of wavelength sensitivity and amplitude sensitivity than some previous reported sensors. We believe that it can become a favorable competitor in the liquid RI measurement fields. [ABSTRACT FROM AUTHOR]

• The D-shaped microstructure fiber sensor is suitable for external plasmonic sensing. • The fiber sensor performs sensing detection by means of double resonance peaks. • The fiber sensor has high sensitivity, high resolution and high figure of merit at the near-infrared wavelength. • Double-peaks detection is simultaneously self-calibrated as both detection and verification. A miniature D-shaped microstructure fiber sensor is proposed for external plasmonic sensing. The hollow core not only effectively modulates the core field, but also efficiently facilitates the excitation of surface plasmon resonance near the micro-opening. The refractive indices of analyte ranging from 1.37 to 1.41 can be detected by double-loss peaks tracing in the near-infrared wavelength. And the more reliable method of double-peaks detection achieves detection and verification simultaneously, which improves largely the accuracy of sensing detection. In addition, the transmission properties and sensing characteristics for the designed sensor is explored as well corresponding to various geometrical parameters. An average wavelength sensitivity is 26,927 nm/RIU with the resolution of 3.71 × 10−6 RIU, and the maximum amplitude sensitivity of 5059 RIU−1 is obtained with the resolution of 1.97 × 10−6 RIU, moreover, the maximum figure of merit can reach to 1282, which can be found a wide application prospect in the field of chemical, biological and medical. [ABSTRACT FROM AUTHOR]