Regular articleSurface plasmon polariton high-sensitivity refractive index sensor based on MMF-MOF-MMF structure
Introduction
With the continuous development of science and technology and the continuous improvement of people's requirements for daily life, the demand for easy-to-integrate and high-performance sensors has become increasingly urgent. Surface plasmon resonance (SPR) optical sensors have the characteristics of high sensitivity, label-free and real-time monitoring, and are playing an increasingly important role in the fields of biochemistry, medical diagnosis, food safety and homeland security. The SPR-based optical fiber sensor also has the advantages of simple structure, small size and light weight, which further broadens the application prospect of SPR sensors [1], [2], [3], [4].
Currently, many fiber optic SPR sensors have been developed, such as D-shaped fiber [5], etched fiber [3], and U-shaped fiber [6]. Jang et al. [7] studied a gold-coated few-mode fiber sensor, and achieved a refractive index sensitivity of 2500 nm/RIU within the refractive index detection range of 1.33–1.412. Ben et al. [8] etched the cladding of a thin core single-mode fiber (TC-SMF) to enhance the leakage intensity of the evanescent field, and proposed a refractive index sensor with SMF-TCSMF-SMF structure. When the RI detection range is 1.333–1.340, its sensitivity is 857.5 nm/RIU. Zhang et al. [9] studied a graphene/AgNPs U-shaped optical fiber SPR sensor with a refractive index sensitivity of 1198 nm/RIU. However, the realization of sensing through side polishing and corrosion of the fiber structure will undoubtedly increase the cumbersomeness of the manufacturing process, and due to the damage to the mechanical strength of the optical fiber, the fiber will become very brittle, which is not conducive to subsequent production, packaging and use.
In this paper, a SPR-inducted refractive index sensor based on the MMF-MOF-MMF structure is presented. In order to generate SPR, a silver film is coated on the sensing region by an easy to implement and low-cost silver mirror reaction method. In the RI detection range of 1.3328–1.3990, the linearity of 0.96912 and the high refractive index sensitivity of 3223 nm/RIU can be achieved. At the same time, the SPR sensor based on the MMF-MOF-MMF structure has a simple structure and good stability and repeatability. Therefore, it can be used in the fields of environmental monitoring, industrial production and food safety related to refractive index detection.
Section snippets
Experimental principle
When light propagates from MMF to MOF, since the core diameter of MMF is much larger than that of MOF and the existence of the collapsed region connecting MMF and MOF, part of the light will propagate from the MMF core to the MOF cladding and excite higher-order modes to the cladding/silver film interface for SPR [10]. When the incident light propagating in the MOF is totally reflected at the cladding/silver film interface, part of the light will decay exponentially with the incident depth,
Fabrication of MMF-MOF-MMF SPR sensor
In order to help understand the resulting sensitivity, the end face of MOF captured under the optical microscope is processed and imported into Comsol Multiphysics software to study its electric field distribution. Fig. 1(a) and (b) illustrate the cross-section of MOF under the optical microscope and the cladding mode filed of MOF at the wavelength of 0.5 μm. The air-holes range and cladding diameter of MOF are 62 and 162 μm, respectively. The core and cladding diameters of MMF are 62.5 and
Conclusions
A kind of SPR refractive index sensor based on MMF-MOF-MMF structure is proposed. With the increase of the refractive index, the transmission spectrum of the sensor has a significant red shift, and the resonance wavelength shift is 218.11 nm with the sensitivity as high as 3223 nm/RIU. In addition to the advantages of simple fabrication, easy operation and low cost of the chemical coating method based on the silver mirror reaction, the sensor also has high sensitivity, good stability and
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was supported by National Natural Science Foundation of China (12074331), the Program of the Natural Science Foundation of Hebei Province (Grant No. F2017203193, F2020203050), the Postdoctoral preferred funding research project of Hebei Province (Grant No. B2018003008), and the Postgraduate Innovation Research Assistant Support Project (Grant No. CXZS202010).
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