Surface Plasmon Resonance (SPR) based fiber optic curvature sensors have the advantage of being insensitive to temperature and axial strain. However, they have the disadvantage of low sensitivity and small curvature detection range. To improve the performance of SPR curvature sensors, we propose an intensity-modulated microstructured optical fiber (MOF) curvature sensor. In this sensor, two no-core fibers (NCFs) are used as input-output couplers, and MOF with silver film deposited is used as sensing arms. The light in the cladding is used to excite the SPR, and the exciting resonant valley is extremely sensitive to slight bending changes. The performance of this sensor is investigated theoretically and experimentally. Numerical results show that its cladding pattern is more favorable in the excitation of SPR effects. Experimental results show that the cladding mode of MOF is very sensitive to curvature changes, thus giving it a great advantage in bending measurements. Its sensitivity reaches 0.18 dB/m^-1, and linearity reaches 0.995 in the curvature range of 0-30 m^-1. The sensor has the advantages of high sensitivity, low temperature and axial strain crosstalk, compact structure, and easy fabrication, which make it attractive in the field of bending sensing.

A twin-core photonic crystal fiber sensor is proposed for measuring liquid refractive index (RI) and temperature simultaneously. The air holes of the sensor are arranged in a hexagonal pattern, and two planes are introduced by polishing in the cladding. On one side of the plane, the gold film is deposited for RI measurement, and on the other side, the gold film and polydimethylsiloxane are deposited for temperature measurement. We analyzed its sensing characteristics by using the finite element method. The numerical results show that the two channels for measuring RI and temperature have no mutual interference and the arrangement reduces the complexity of the sensing measurement. The maximum spectral sensitivity of the sensor is 20 000 nm/RIU and 9.2 nm °C⁻¹, respectively, when the liquid RI is in the range of 1.36–1.42 and the temperature is in the range of 0 °C–50 °C. The results also show the sensing accuracy was not very sensitive to the change of structural parameters, which makes the sensor very easy to fabricate. Our work is very helpful for implementation of a high sensitivity, easy fabrication and real-time multi-parameter surface plasmon resonance sensor.

Molybdenum disulfide (MoS₂), as a representative transition metal disulfide material, has contributed significantly to the development of plasmonic technology toward the near-infrared (NIR). In this Letter, the physical mechanism of MoS₂ excitation of surface plasmon resonance (SPR) in the NIR is investigated, and it is shown that the MoS₂ film can induce the resonance dip to move toward the NIR and demonstrate a sensitivity higher than that in the visible band. A dual-channel SPR sensor capable of operating in the visible and NIR bands for refractive index (RI) detection was also prepared using the cascade method. The simulated and experimental results of the sensor show consistency. The experimental results show that the maximum sensitivity of the NIR detection channel is 14600 nm/RIU in the RI range of 1.333–1.420, which is 37% higher than the sensitivity of the visible channel. However, the visible channel has the advantage of a narrow FWHM. Therefore, the proposed cascaded dual-channel RI sensor combines high sensitivity and narrow FWHM. This dual-channel construction method improves the detection level of RI, promotes the development of SPR sensing technology to the NIR band and significantly improves the narrowband problem existing in the previous multi-channel sensing.

In order to broaden the sensing bandwidth of surface plasmon resonance (SPR) sensors, we propose and demonstrate a dual-channel SPR fiber optic sensor with wide bandwidth. The sensor is fabricated using no-core fiber (NCF), in which the film consists of a silver film and a ZnO film. The sensing characteristics are investigated by simulation and experiment. The resonance wavelength range of the SPR sensor can be significantly tuned by varying the thickness of the ZnO film. In the experiments, a dual-channel SPR sensor that can be used for simultaneous detection of temperature and refractive index was realized by cascading ZnO/Ag film with Ag film. The experimental results show that the two sensing channels are independent without crosstalk. The sensitivity of this sensor is 3512 nm/RIU in the range of 1.333 ∼ 1.385 and 4.6 nm/°C in the range of 0 ∼ 60 °C, which is better than most of the current dual-channel SPR sensors. In addition, the experimental results show that this sensor has good stability in use. The sensor proposed in this work has the advantages of a wide operating wavelength range, simple and compact structure, and high sensitivity. It has a broad application prospect in the simultaneous measurement of refractive index and temperature of liquids.