This paper proposes a fiber optic surface plasmon resonance (SPR) sensor based on the heterostructure of MoS2/WS2. Transition metal dichalcogenides (TMDCs) have been widely studied due to their high carrier mobility, excellent photoelectric properties and good biocompatibility. A heterostructure is constructed by two types of TMDCs (MoS2/WS2) and is used to improve the performance of the Ag layer coated fiber optic SPR sensor. The heterostructure film increases the integral of the electric field intensity on the surface of the sensor, thus improving the sensitivity of the sensor. The finite element analysis shows that the sensitivity of the sensor is as high as 3127.18 nm/RIU and the figure of merit is up to 70.04 RIU-1. The proposed sensor exhibits promising potential in the field of biochemical detection.
In this work, we employed the Empirical mode decomposition (EMD) algorithm into the demodulation spectrum of the long period fiber grating sensing experiment. After data processing by the EMD-based filtering algorithm, the disordered noise of the fiber Bragg fiber grating (LPFG)’s spectrum caused by the laser source and mode coupling can be effectively eliminated so that the single valley wavelength of LPG can be much more precisely located. As a consequence, based on the proposed algorithm, the related sensitivity of refractive index solution detection can be reached 11 nm/RIU, 18 nm/RIU, 61.3 nm/RIU and 241 nm/RIU in 1.33-1.36, 1.37-1.39, 1.40-1.43, and 1.43-1.45 refractive index region, respectively.
The performance of an optic fiber SPR sensor is affected by the optical property of the metal layer. The optical property of the metal layer is affected by the surface morphology and the grain structure of itself. In this paper, the optical property of metal film based on the Drude-Lorentz model is improved by employing the Fuchs-Sondheimer theory and the Mayadas-Shatzkes theory. In the new law, the surface roughness and the grain structure are taken into account to describe the permittivity of metal layer theoretically. Then the improved model is used to analyze the performance of the optical fiber SPR sensor. The results shows that the surface roughness and the grain structure of metal layer significantly affect the resonance properties of the sensor. Specifically, the surface roughness of metal film can change the resonance wavelength of the SPR sensor. When the surface becomes smooth, resonance wavelength of SPR will decrease. In addition, with the increasing of grain size, the depth of the SPR curve increases obviously, while the full width at half maximum of the sensor decreases a lot. It means that, for a certain metal layer, the effects of the surface roughness and the grain structure should be considered in SPR technique.
Tungsten disulfide (WS2) nanosheets is a promising two-dimension (2D) material for offering lots opportunities in the development of new biological and chemical sensors and sensing strategies. Fiber SPR sensor is a powerful tool in the field of biology and chemistry. In this work, we simulated the effect of different tickness WS2 nanosheets on the fiber SPR sensor. The result show that, the SPR sensor perform best when WS2 nanosheets is 9.6 nm. Its refractive index sensitivity is 2018.4nm/RIU, the full width at half maximum is 151.4 nm, and the quality factor is 1.333.
Surface Plasmon resonance (SPR) technique is gradually growing as a research focus in optical area, which has been widely applied in many disciplines. The fiber-based SPR sensor, combining the advantages of fiber and SPR phenomenon, will lead to more tremendous application areas. The design and fabrication of different fiber SPR sensors are always be focuses of researchers in recent year, but the characteristic wavelength demodulation of the SPR sensor didn’t obtain enough attention. In this paper, the detection system for a fiber-based SPR sensor was presented first, and the detection mechanism of the refractive index sensing was obtained theoretically. Based on the theoretical simulation and analysis, the analytical expression of the all-phase low-pass filters was deduced, which is used for the de-noising of the original spectrum for the SPR sensing system, leading to resonance wavelength extraction only by calculating the derivative of the de-noised signal. So the resonance wavelength of the SPR sensor can be easily obtained by using this simple demodulation algorithm. Based on the realization of the system, the refractive index sensing of alcohol solution was carried out. And a good linear relationship between the refractive index of the solution and the characteristic wavelength of the SPR sensor can be obtained, with refractive index sensitivity and fitting error of 2048.5 nm/RIU and 5.69 nm respectively.
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