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光纤SNS-SPR传感器,如图1所示。传感器的光纤结构由两段单模光纤中间夹心熔接一段长度为12 mm无心光纤(台湾卓越成功公司)组成。由于两种光纤的纤芯不匹配对接,使得进入无心光纤中的单模光束激发起了多个高阶模式。一方面这些高阶模式到达无心光纤表面形成表面倏逝场,我们在无心光纤表面沉积45 nm的金传感层,当金传感层中的自由电子波矢KSPR与倏逝场的入射波矢分量Kz相等时,SPR发生,入射光被吸收,同时金传感层中的等离子体波激发。
$${K_{{\rm{SPR}}}} = \frac{{2\pi }}{\lambda }\sqrt {\frac{{{\varepsilon _m}(\lambda ){\varepsilon _e}}}{{{\varepsilon _m}(\lambda ) + {\varepsilon _e}}}} $$ (1) $${K_{\rm{Z}}} = \frac{{2\pi {n_c}\sin \theta }}{\lambda }$$ (2) 式中:εm(λ)和εe分别为金传感器和被探测外部介质的介电常数,且εm(λ)随光波长λ的变化而变化;nc是无心光纤的折射率。SPR吸收的光波长随被探测外部介质的改变而移动。
另一方面,无心光纤中传输的多个模式再次汇入单模光纤时会产生多模干涉,干涉模式满足以下条件:
$$2\pi \Delta n_{eff}^{m,n}L/\lambda = 2\pi N$$ (3) 式中:
$\Delta n_{eff}^{m,n}$ 为不同模式间的有效折射率差;m和n是模式的阶数;L为无心光纤的长度;λ为光波长;N是整数。多模干涉光谱将叠加于SPR光谱,在本传感器设计中不利于SPR检测信号的提取,应该设法消除。实验制备了三种不同规格的光纤SNS-SPR传感器,通过改变无心光纤的芯径(125 μm,80 μm,61.5 μm)来设计传感区。采用经典的直接透射传输系统对不同传感器进行测试比较。输入端的光源采用白光光源(ThorLabs, SLS 201L/M),输出端的探测器采用可见光光谱仪(Ocean Optics, USB 4000)。
Single mode-no core-single mode fiber based surface plasmon resonance sensor (Invited)
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摘要: 光纤表面等离子体共振(SPR)传感器结合了光纤传感器的微型化、可在线传输、易操作和SPR生物检测技术的高灵敏、高选择性、免标记等优势,是当前免疫学生物传感器的研究热点。但传统多模光纤SPR传感器的信号在远距离传输中易损耗、失真。文中提出了一种单模-无心-单模光纤型SPR传感器,能有效减小信号传输中的损耗与失真,且适合与当前的光纤网络衔接。为了消除传感器中的干扰信号,改变无心光纤的芯径,采用去除背景干扰,高斯拟合等方法,最终选取了具有芯径为61.5 μm无心光纤的此类传感器,并从中提取出了有效的SPR光谱信号。传感器的灵敏度为1153.40 nm/RIU,分辨率为1.70×10−4 RIU。此类光纤生物传感器的成功开发,为智慧医疗、远程医疗提供了一种新的思路。Abstract: Optical fiber surface plasmon resonance (SPR) sensor combines the advantages of optical fiber sensor like miniaturization, online transmission, easy operation and SPR biodetection technology, which is highly sensitive, highly selective and label-free. It is currently a research hotspot of immunological biosensors. However, the signal of traditional multi-mode fiber based SPR sensor is easy to be lost and distorted in long-distance transmission. In this paper, a single mode-no core-single mode fiber based SPR sensor was proposed, which could effectively reduce the loss and distortion in signal transmission, and was suitable for connecting with the current optical fiber network. In order to eliminate the interference signal in the sensor, the core diameter of the no core fiber was changed, the methods of removing background interference and Gaussian fitting were adopted, and finally the sensor with the sensing region of 61.5 μm no core fiber was selected, the effective SPR spectrum signal was extracted from it. The sensitivity of proposed sensor is 1153.40 nm/RIU and the resolution is 1.70×10−4 RIU. The successful development of this kind of optical fiber biosensor provides a new idea for intelligent medical treatment and telemedicine.
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Key words:
- optical fiber SPR sensor /
- refractive index /
- multimode interference
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图 5 高斯拟合下的61.5 μm光纤SNS-SPR传感器的检测性能:(a) 1.3344折射率下的相对光谱高斯拟合,插图为高斯拟合后SPR吸收峰随折射率的变化;(b)灵敏度
Figure 5. Performance of the optical fiber SNS-SPR sensor with 61.5 μm no core fiber after Gaussian fitting: (a) Gaussian fitting of relative spectrum at the refractive index of 1.3344, the illustration shows the change of SPR dip with refractive index; (b) sensitivity
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