Curvature measurement plays an important role in many fields. Aiming to overcome shortcomings of the existing optical fiber curvature sensors, such as complicated structure and difficulty in eliminating temperature noise, we proposed and demonstrated a simple optical fiber curvature sensor based on surface plasmon resonance. By etching cladding of the step-index multimode fiber and plating gold film on the bare core, the typical Kretschmann configuration is implemented on fiber, which is used as the bending-sensitive region. With increases in the curvature of the optical fiber, the resonance wavelength of the SPR (Surface Plasmon Resonance) dip linear red-shifts while the transmittance decreases linearly. In the curvature range between 0 and 9.17 m−1, the wavelength sensitivity reached 1.50 nm/m−1 and the intensity sensitivity reached −3.66%/m−1. In addition, with increases in the ambient temperature, the resonance wavelength of the SPR dips linearly blueshifts while the transmittance increases linearly. In the temperature range between 20 and 60 °C, the wavelength sensitivity is −0.255 nm/°C and the intensity sensitivity is 0.099%/°C. The sensing matrix is built up by combining the aforementioned four sensitivities. By means of the dual modulation method, the cross-interference caused by temperature change is eliminated. Additionally, simultaneous measurement of curvature and temperature is realized.

By using a seven-core fiber (SCF), we propose and demonstrate a novel segmented detection SPR sensor, which solves two bottlenecks about the fiber SPR sensor of low sensitivity and the difficulty in the multichannel detection. The proposed sensor has ultra high sensitivity and wide detection range because of employing the segmented detection technology. Besides that, the proposed sensor employs reflection-type time division multiplexing (TDM) technology in fiber multichannel detection for the first time. We couple light into and out of the six circularly symmetric distributed cores of the seven-core fiber to realize the three channel SPR sensing and testing. This three-channel SPR sensor has the advantages of detecting biochemical or multi analytes reactions and eliminating the distractions due to temperature fluctuations or sample composition variations and adsorption of non-target molecules to the sensor surface. This SPR sensor also has the advantages of online monitoring by inserting into the blood vessel because of its small size. Furthermore, this paper has deeply researched the relationship between the refractive index of the solution to be measured, the grinding angle of the sensing channel, the sensitivity and the detection range. In this paper, we propose a novel segmented detection method which realizes the wide detection range with the wider refractive index range of 1.333~1.395 and the narrower working bandwidth of 250nm compared with the common SPR sensor, the average sensitivity and the maximum sensitivity of the sensor reach 7387.1nm/RIU and 8502.5nm/RIU respectively.

Purpose This paper aims to clarify the relationship between the performance of the metal nanoparticles and the sensitivity of the fiber surface plasma resonance (SPR) sensor. It proposes modeling the sensing effects of a single-mode fiber SPR sensor with a cone angle structure decorated with metal nanoparticles. This study uses the metal nanoparticles to the realize enhanced sensitivity of refractive index sensing. Design/methodology/approach This paper opted for an exploratory study using a simulation approach of finite-difference time-domain (FDTD). Specifically, the effect of size, the material and the shape of the metal nanoparticle on sensing performance are investigated theoretically. Findings In conclusion, it is evident that the localized SPR (LSPR) effect weakens as the diameter of the gold nanosphere increases, the SPR effect enhances and the SPR sensitivity increases first and then decreases. The metal nanoparticle with the different materials and different shapes also have different LSPR and SPR sensitivity and wavelength length dynamic range. The investigation shows that, by changing parameters, the reflection spectra of the fiber SPR sensor exhibit an obvious transition from LSPR to SPR characteristics, and enhanced sensitivity of the refractive index is realized. Originality/value This paper fulfills an identified need to study how the sensitivity of the fiber SPR sensor can be enhanced by the metal nanoparticle. After the optimization of parameters, the sensitivity of 5,140 nm/RIU is achieved, which provides a new research direction for sensitivity enhancement of fiber SPR sensor.

In this paper, a refractive index sensor based on the control of the fiber core refractive index is proposed. By employing ultraviolet curable adhesive with the different refractive index and hollow capillary fiber, the special fiber with a variable core refractive index is fabricated. Using the special fiber, a novel, to the best of our knowledge, refractive index surface plasmon resonance (SPR) sensor with a controllable detecting range of refractive index is realized. Functional testing of the sensing probes with the core refractive indices of 1.590, 1.516, and 1.454 is performed respectively, indicating that their sensitivities are 1580 nm/RIU, 2220 nm/RIU, and 3467 nm/RIU, respectively, and their detecting ranges of refractive index are 1.385–1.435 RIU, 1.365–1.415 RIU, and 1.335–1.385 RIU, respectively. Furthermore, in order to explore the detection effect of the sensing probe with the higher-core refractive index, we conducted theoretical calculation using the Kretchmann model. The experimental and simulating results indicates that, with the increase of the core refractive index, the magnitude of refractive index that can be detected increases. This study provides a new method for the detection of high refractive index solutions and a new idea for the fabrication of wavelength-division multiplexing distributed SPR sensors.

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