光纤布拉格光栅嵌入SMS光纤结构的湿度传感器

提出了一种基于光纤布拉格光栅嵌入单模-多模纤芯-单模(single-mode-multimode fiber core-single mode, SMS)光纤结构的湿度传感器。当环境湿度变化时,SMS光纤结构的干涉光谱会发生漂移,而光纤布拉格光栅对湿度不敏感,其纤芯基模保持不变。因此利用SMS光纤结构对环境湿度的敏感性去调制光纤布拉格光栅纤芯基模,通过检测光纤布拉格光栅纤芯基模的反射能量变化就可以实现湿度测量。数值模拟了SMS光纤结构的内部光场分布规律,理论计算了不同环境折射率时,多模纤芯的长度、直径对SMS光纤结构输出能量耦合系数的影响。理论模拟表明,随着环境折射率变化,SMS光纤结构中传输的纤芯基模的输出能量耦合系数会发生变化。同时制作了传感器样品并对其进行了传感实验研究,实验结果表明多模纤芯长35 mm、纤芯直径为85 μm的传感器在45%～95%RH湿度变化范围内,湿度灵敏度为0.06 dBm·(%RH)-1。在20～80 ℃温度范围内,传感器的温度灵敏度为0.008 nm·℃-1,温度所带来的湿度测量误差为0.047%RH·℃-1。传感器具有制作简单、灵敏度高、反射式能量检测等优点,在湿度测量领域有一定的应用价值。     

Temperature-independent refractometer based on fiber-optic Fabry–Perot interferometer

A miniature fiber-optic refractometer based on Fabry–Perot interferometer (FPI) has been proposed and experimentally demonstrated. The sensing head consists of a short section of photonics crystal fiber (PCF) spliced to a single mode fiber (SMF), in which the end-face of the PCF is etched to remove holey structure with hydrofluoric (HF) acid. A Fabry–Perot interference spectrum is achieved based on the reflections from the fusion splicing interface and the end-face of the core of PCF. The interference fringe is sensitive to the external refractive index (RI) with an intensity-referenced sensitivity of 358.27 dB/RIU ranging from 1.33 to 1.38. The sensor has also been implemented for the concentration measurement of λ-phage DNA solution. In addition, the dip intensity is insensitive to the ambient temperature variation, making it a good candidate for temperature-independent bio-sensing area.     

All-fiber refractometer based on core mismatch structure

We demonstrate a novel all-fiber refractometer which is a multimode-single mode-multimode (MM-SM-MM) fiber structure formed by splicing a section of uncoated single mode fiber (SMF) with two short sections of multimode fibers (MMFs). Owing to the core mismatch at the splicing points of the SMF with two sections of MMFs, part of the guided light propagates in the cladding of the SMF, which makes the SMF sensitive to the external refractive index (RI). RI sensing is achieved by measuring the wavelength shift of the interference pattern of the cladding mode and the core mode of the SMF. A RI sensor with an average sensitivity of 412 nm/RUI (refractive index unit) for a RI range from 1.333 to 1.400 is presented.     

Compact FBG diaphragm accelerometer based on L-shaped rigid cantilever beam

A compact fiber Bragg grating(FBG) diaphragm accelerometer based on L-shaped rigid cantilever beam is proposed and experimentally demonstrated.The sensing system is based on the integration of a flat diaphragm and an L-shaped rigid cantilever beam.The FBG is pre-tensioned and the two side points are fixed,efficiently avoiding the unwanted chirp effect of grating.Dynamic vibration measurement shows that the proposed FBG diaphragm accelerometer provides a wide frequency response range(0-110 Hz) and an extremely high sensitivity(106.5 pm/g),indentifying it as a good candidate for embedding structural health monitoring and seismic wave measurement.     

具有温度自校准功能的光纤折射率传感器

提出一种具有温度自校准功能的光纤折射率（RI）传感器,传感头结构由2段很短的多模光纤（MMF）之间夹熔一段对折射率不敏感的光纤布拉格光栅（FBG）构成,传感头总长度为14 mm,FBG可以为折射率测量提供良好的温度校准功能。实验结果证明,该传感器的折射率灵敏度为126 nm。其干涉光谱共振波长的温度灵敏度为35.09 pm/℃,用于温度校准的FBG的温度灵敏度为11.14 pm/℃。相比于普通的折射率传感器,这种具有温度自校准功能的折射率传感器具有良好的实用前景。     

Refractive index and temperature sensing characteristics of an optical fiber sensor based on a tapered single mode fiber/polarization maintaining fiber

An evanescent field optical fiber sensor based on a short section of polarization maintaining fiber spliced with a tapered single mode fiber is proposed and experimentally investigated. We mainly focus on the refractive index(RI) and temperature sensing characteristics of this compact device. The transmission spectrum of the resonance wavelength,induced by the interference between the excited low order cladding modes and core modes,shows the quadratic function relationships with RI and linear relationships with temperature. Thus,the proposal of this simple-to-fabricate,compact,and low cost sensor shows its possible potential in the sensitive detection field.     

Reflective fiber-optic refractometer based on a thin-core fiber tailored Bragg grating reflection

A novel reflective refractometer based on a thin-core fiber (TCF) sandwiched between a leading single-mode fiber (SMF) and a fiber Bragg grating (FBG) imprinted SMF stub was demonstrated. The reflection from the fiber stub occurs in two well-defined wavelength bands, corresponding to the Bragg core mode and cladding modes. The TCF section functions as a tailorable bridge between the FBG core mode reflection and the surrounding refractive index (SRI). Linear response with enhanced sensitivity of 133.26 dB/refractive index unit for temperature-immune SRI measurement within the biologically desirable sensing range of 1.33-1.41 has been achieved via cost-effective power detection.     

Fiber refractometer based on a fiber Bragg grating and single-mode-multimode-single-mode fiber structure

A refractive index (RI) sensor based on a novel fiber structure that consists of a single-mode-multimode-single-mode (SMS) fiber structure followed by a fiber Bragg grating was demonstrated. The multimode fiber in the SMS structure excites cladding modes within output single-mode fiber (SMF) and recouple the reflected cladding Bragg wavelength to the input SMF core. By measuring the relative Bragg wavelength shift between core and cladding Bragg wavelengths, the RI can be determined. Experimentally we have achieved a maximum sensitivity of 7.33 nm/RIU (RI unit) at RI range from 1.324 to 1.439.     

Spectrum-profile-identification-based wavelength division multiplexing method for a fiber Bragg grating sensor

A new wavelength division multiplexing method for fiber Bragg grating(FBG) sensors based on spectrum profile identification is proposed. In this method, FBGs and tilted FBG(TFBG) sensors are cascaded in a single fiber in one sensing channel. The different spectrum profiles enable the cross-correlation method to demodulate the wavelength. Therefore, the different types of sensors can occupy the same central wavelength band. Using this method, the multiplexing capacity is optimized. Experiment results demonstrate the feasibility of this method and it is useful for applications where large numbers of FBGs are needed.     

Design and analysis of a new silicon-on-insulator waveguide Michelson interferometer sensor

A new designed and analyzed silicon-on-insulator (SOI) waveguide Michelson interferometer (SMI) sensor is proposed in this paper. The authors compare an optical SMI sensor, a silicon-on-insulator Bragg waveguide grating (SBG) sensor, and a fiber Bragg grating sensor (FBG) for temperature sensing in medicine applications. The SMI sensor has 20 times sensing more accuracy than the FBG sensor. Moreovr, the full width at half maximum (FWHM) of the pass-band frequency responses of our proposed SMI can be designed much narrower than FBG and SBG sensors for sensing resolution enhancement. Further, the improved characteristics of the SMI demonstrated in this paper could pave the way for future high density temperature monitoring medicine applications.     

Compact microfiber Bragg gratings with high-index contrast

We fabricate fiber Bragg grating (FBG) in microfibers (MFs) using focused ion beam milling technique. By periodically etching 100 nm-depth grooves on the surface of silica MFs with diameters less than 2 μm, evident grating features with transmission dip up to 15 dB are obtained. Because of the high-index contrast of the gratings structure, the length of the microfiber Bragg grating (MFBG) can be reduced to 500 μm level. Using a 518 μm-length 1.8 μm-diameter MFBG, we also demonstrate sensitivity up to 660 nm per refractive index unit (RIU) for refractive index (RI) sensing. The highly compact MFBGs demonstrated here may serve as low-dimensional building blocks for miniaturized photonic components and devices.     

FBG多功能传感系统集成与应用

为充分发挥光纤光栅(FBG)传感系统复用能力,可同时对传感光路各个传感器的光信号进行有效识别,且为传感器设计和加工提供依据,基于FBG传感原理,从系统集成及复用能力优化的角度,探讨波分复用传感器设计方法,以及节点传感器结构和灵敏度设计原则与标准,并将提出的原则等应用于某实际工程光纤监测系统。传感系统在运行过程中,获得了较为可靠的监测数据,分布式光纤和点式电测技术测试结果相差6%左右,进一步表明临近光纤传感器没有出现传感信号串扰现象,为工程施工和安全维护提供参照。     

光纤光栅啁啾化传感研究

提出了光纤光栅啁啾化传感概念和传感机理,将光纤光栅微观分解为栅区长度范围的许多具有独立感知能力且彼此关联的有效作用子栅集,表述了有效作用子栅集与待测环境场空间梯度分布之间的对应关系,从而较好地解释了光纤光栅啁啾谱产生的内在机理.理论推导并实验验证了光栅啁啾谱各谱参量(波长、带宽和反射光强)与待测环境场(温度和应变)之间的对应关系,为利用单一光纤光栅实现多参量同时区分测量、任意非均匀空间分布场传感提供了科学有效的解决方法.     

动态匹配光栅解调方法波长读出优化研究

提出了采用一支价格低廉的微测力传感器作为匹配光栅解调系统的波长读出单元,不同于以往动态匹配光栅解调法采用拉伸匹配光栅的PZT驱动电压作为解调系统波长读出单元.当匹配光栅和传感光栅布喇格中心波长重叠时,光电探测器将接收到最大光信号.利用光纤光栅轴向受力和反射波长漂移的数学关系得到光纤光栅传感器的波长漂移.该解调系统解决了传统动态匹配解调系统中PZT本身特性对系统的影响,探测到的光纤光栅传感器反射波长和匹配光栅轴向受力大小具有很好的线性,系统线性大于0.999.本系统对于探测布喇格传感器应变分辩率达到1 με以下.     

Dynamic strain measurement using two wavelength-matched fiber Bragg grating sensors interrogated by a cascaded long-period fiber grating

In this work, we describe a fiber Bragg grating (FBG) sensing system using two wavelength-matched FBG sensors for static and dynamic strain measurement. A cascaded long-period fiber grating (CLPG)-based demodulation technique has been used to interrogate the two wavelength-matched FBG sensors. Experimental results of static strain measurement show that the proposed system has a strain resolution of 1 με. This system has also been used for dynamic strain measurement. An eddy current displacement meter-based system has been used as a comparison measurement. Experimental results of dynamic strain measurement have proved that the FBG sensing system has a good performance in the measurement of dynamic strain. The results of static and dynamic strain measurement indicate that the sensing system using two wavelength-matched FBG sensors is superior to the single FBG sensor system.     

Refractometer based on a tapered Mach–Zehnder interferometer with Peanut-Shape structure

A novel refractometer based on tapered Mach–Zehnder modal interferometer (MZI) is proposed and experimentally demonstrated. This sensor is composed of a pair of Peanut-Shape structures and an embedded taper – the former excites high-order cladding modes, while the latter enhances the evanescent field. As the effective refractive index (RI) of cladding is based on the changes of surrounding RI, thus extinction ratio will change due to the alteration of the distribution of power in the fiber which is induced by various differences of core and cladding for RI. As a result, the maximum RI sensitivity of 240.78 extinction ratio/RIU (refractive index unit) is achieved within the range from 1.3334 to 1.4081.     

基于结构化光纤Bragg光栅的折射率梯度传感器研究

研究结构化光纤Bragg光栅(FBG)在折射率(RI)呈线性分布的液相介质环境下的响应特性。数值仿真结果表明,结构化FBG的反射谱特性强烈依赖于液相介质折射率(RI)的线性分布函数的某些特征参数,比如液相介质的RI沿FBG轴向的分布梯度、RI在FBG两端的差值等。基于理论仿真结果,建立了结构化FBG在低RI区(1.330～1.360)对液相介质的RI梯度进行测量的线性近似理论模型。通过相关实验研究,证明了理论仿真和分析的合理性及基于结构化FBG的RI梯度传感器在现实应用中的可行性。     

一种单模-多模-单模结构的干涉型光纤温度传感器

SMS光纤结构是一种近年来新兴的光纤器件,该结构光纤具有结构简单、易于实现、成本低廉、灵敏度高和无温度应力交叉敏感等特性.在光纤传感技术领域是一种继光纤光栅之后的具有广泛发展前景的光纤器件.从理论上分析了SMS结构和SMS级联结构的光纤传感原理,并从实验上研究了SMS结构和级联SMS结构的温度传感特性.实验表明:对于SMS结构光纤传感器,随着温度的增加,特征波长移动量逐渐增加,向长波方向漂移了4.05 nm,其传感器的温度灵敏度为15.76 pm/℃;对于级联SMS结构的光纤传感器,级联后不改变原来SMS结构的中心波长的位置,两个SMS结构仍然是独立的,不相互影响.所以说将两个SMS结构串联是可行的,可以用于温度和应力的同时测量,也可以用于分布式光纤传感器.     

基于光纤光栅的一体式靶式流量传感技术

针对以往液压系统检测中存在的特点,如结构杂、体积大、精度低,设计了一种基于光纤布拉格光栅(FBG)的一体式靶式流量传感器。分析了FBG及靶式流量传感原理,设计出一种组成紧凑、便于密封以及拆装的一体式靶片,将放在流体里的靶片受到的与流速成相关变化的冲击力变为FBG波长的漂移,双FBG对称分布,分别放在悬臂梁两表面中轴线处,这种差动形式可以很好地增加灵敏度,并且可以解决应变和温度的交叉敏感现象。通过FLUENT分析了流体形式,结果显示这种结构给流体造成的影响比一般结构小。实验测试过程中,双FBG中心波长总变化数值和放置于靶片的质量呈现出明显的线性变化,并且灵敏度为一个FBG灵敏度的双倍,可靠性以及稳定性较好。     

光纤光栅传感器的应用

在光纤传感领域，光纤光栅传感技术是十多年来发展最为迅速的技术之一，传感系统本身和应用领域均有了很大发展．文章介绍了光纤光栅的结构、性能以及传感的原理，回顾了光纤光栅传感器在地球动力学、航天器及船舶航运、民用工程结构、电力工业、医学、和化学传感中的应用．