高灵敏度光纤应变传感器

提出一种基于锥形光纤和光纤F-P腔组合结构的光纤应变传感器。该传感器包含单模光纤拉锥形成的锥区和石英毛细管构建的F-P腔2个应变敏感区域。理论分析了光波在该传感器中的传播过程,获得了该传感器的光强传输函数。由于锥形光纤中激发出的包层高阶模参与干涉,导致传感器干涉光谱具有调制特性。实验获得了该传感器的干涉光谱,通过分析谐振波长偏移或消光比变化对应变实现独立测量,在0~500 με的测量范围内,该传感器的应变灵敏度为14.6 pm/με。利用锥形光纤引发的模式干涉和F-P腔的双光束干涉效应共同作用形成受调制的干涉谱型进行应变传感,应变灵敏度高,同时具备2种独立的应变检测手段(谐振波长和消光比检测)。     

Compact optical fiber curvature sensor based on concatenating two tapers

A low-loss, compact, and highly sensitive optical fiber curvature sensor is presented. The device consists of two identical low-loss fused fiber tapers in tandem separated by a distance L. When the optical fiber is kept straight and fixed, no interference pattern appears in the transmitted spectrum. However, when the device is bent, the symmetry of the straight taper is lost and the first taper couples light into the cladding modes. In the second taper, a fraction of the total light guided by the cladding modes will be coupled back to the fundamental mode, producing an interference pattern in the transmitted spectrum. As the fiber device is bent, visibility of the interference fringes grows, reaching values close to 1. The dynamic range of the device can be tailored by the proper selection of taper diameter and separation between tapers. The effects of temperature and refractive index of the external medium on the response of the curvature sensor is also discussed.     

A Raman laser intensity sensor induced by the cooperative Rayleigh scattering in a ring configuration

In this work, a laser sensor is described that uses the multipath interference produced inside a ring cavity to measure the power loss induced by a moving taper intensity sensor. The laser is created due to the virtual distributed mirror formed by the Rayleigh scattering produced in a dispersion compensating fiber when pumped by a Raman laser. Two laser peaks were formed, one of them is obtained by the Raman gain (1555 nm) inside the ring and the second is created by the combination of the Raman gain and the Rayleigh scattering (1565 nm). A taper sensor is used as displacement sensor and when the losses is applied in the taper the second laser peak is reduced and the first peak is maintained constant and can be used as reference level.     

Biconical-taper-assisted fiber interferometer with modes coupling enhancement for high-sensitive curvature measurement

A modal interferometer based on multimode–singlemode–multimode fiber structure built with a biconical taper for fiber curvature measurement is proposed and experimentally demonstrated. Due to the tapered singlemode fiber acting as a high-efficient mode power converter to enhance the modes coupling, curvature sensor with improved sensitivity is achieved by monitoring the defined fringe visibility of the interference spectrum. The measuring range can be tuned by changing the waist diameter of the fiber taper. Meanwhile, the sensor shows an intrinsic ability to overcome the influence of temperature cross-sensitivity and the power fluctuation of light source. The advantages of easy fabrication, high-quality spectrum with improved sensitivity, and small hysteresis will provide great potential for practical applications of the sensor.     

用一根光纤光栅实现温度与应变的同时测量

报道了一种用一根光纤光栅实现温度与应变同时测量的新方案。用于同时传感温度与应变的光纤光栅写于两种不同光纤的连接处,本身具有两个反射峰。将其中半个光栅粘于热膨胀系数较大的基底材料上,这样,两个反射峰便具有不同的温度及应变响应,由此实现温度与应变的同时测量。     

Tuning of fiber lasers by use of a single-mode biconic fiber taper

We report a novel scheme to build a compact, tunable fiber laser. The tuning mechanism is based on the transmission property of a single-mode biconic fiber taper. While pulling the taper, we observe oscillations in the transmitted optical power that are due primarily to interference between a pair of excited modes within the tapered region, which are eventually coupled into the unstretched single-mode fiber at the end of the taper. A similar mechanism causes the modulation of the transmitted optical spectrum after the taper has been pulled and stabilized. It is this spectral modulation by the taper that is exploited here to control the wavelength of a fiber laser. The modulation can be adjusted by stretching the taper, thus enabling the tuning of the laser wavelength. We have built a 32 mW Er-doped tunable ring fiber laser with a continuous tuning range of over 20 nm and a signal-to-noise ratio of better than 45 dB over the entire tuning range; our output power is limited only by the available pump power.     

基于光纤锥和纤芯失配的Mach-Zehnder干涉湿度传感器

介绍了一种简单且灵敏度较高的Mach-Zehnder干涉湿度传感器.将单模光纤和多模光纤渐变熔接光纤锥,色散补偿光纤被熔接在两个多模渐变光纤之间,形成了单模光纤-光纤锥-多模渐变光纤-色散补偿光纤-多模渐变光纤-光纤锥-单模光纤结构的传感器.光纤锥起到了增加包层模能量的作用,两个多模渐变光纤节点作为光耦合器,从而形成光纤Mach-Zehnder干涉仪.外界环境湿度的变化,将使得传感器透射谱能量发生变化,通过测量干涉谱波峰峰值能量实现对湿度的测量.实验结果表明干涉谱波峰峰值能量与环境湿度之间存在良好的线性关系.当环境湿度在35%RH—85%RH范围内变化,一段由20 mm色散补偿光纤组成的传感器,其灵敏度为-0.0668 dB/%RH,相关度为0.995.该传感器结构紧凑、尺寸小、制造工艺简单,这使其可以被广泛用于湿度测量.     

锥形光纤装置研究

基于锥形光纤制造过程的复杂性及其传像束的传输性能,利用微机与步进电机相结合,同时控制常用的双坩埚光纤拉丝机出丝管口的直径大小和鼓轮转速快慢,实现了数控拉制1 m长锥形光纤的新方法,并且集束制作出了两种两端不同半径比的锥形光纤传像束.与常用的增大鼓轮体积的方法相比,该装置具有体积小,便于操作,两端半径比可自由控制,断丝率低等特点.分析了这两种锥形光纤传像束的模式损耗。     

Cavity ringdown strain gauge

Biconical tapered single-mode fiber, which is common in many telecommunications components, offers an alternative sensor to typical optical fiber strain gauges that are susceptible to temperature and pressure effects and require expensive and sophisticated signal acquisition systems. Cavity ringdown spectroscopy, a technique commonly applied to high-sensitivity chemical analysis, offers detection sensitivity advantages that can be used to improve strain measurement with biconical tapers. Combining these two technologies in a spatially extended resonator, we demonstrate a minimum detectable change in ringdown time of 0.08%, corresponding to a minimum detectable displacement of 4.8 nm, and a sensitivity to strain as small as 79 n epsilon/square root(Hz) over a 5-mm taper length.     

一种新型的Tapered光纤光栅

利用耦合模方程对正弦型Ｔａｐｅｒｅｄ光纤光栅的反射谱进行了较为详细的计算和分析,并从实验上进行了验证。利用叠加均匀周期光纤光栅的模板和周期性振幅光栏一次成栅的方法,获得了具有三个反射峰、中心波长间隔为０．８ｎｍ的Ｔａｐｅｒｅｄ光纤光栅,这种光栅具有类似于梳状滤波器的功能,在多波长光纤激光器等方面有重要应用。     

正弦锥光纤光栅的数值计算分析

本文利用耦合模方程对正弦锥光纤光栅的反射谱进行了较为详细的计算和分析,发现,这种光纤光栅的反射谱与普通均匀周期光栅的反射谱有着很大的不同,通过控制光栅锥的形状,可得到类似于梳状滤波器的功能,对这种新型光栅在光纤激光器等方面的应用有指导意义。     

Liquid refractive index sensor with three-cascaded microchannels in single-mode fiber fabricated by femtosecond laser-induced water breakdown

Liquid refractive index sensor with three-cascaded microchannels in single-mode fiber was fabricated by femtosecond laser-induced water breakdown. When the liquid is filled in three microchannels across the fiber core, the transmission spectrum of the sensor shows interference peaks. The refractive index of liquid can be sensed accurately based on both the wavelength shift and loss change of interference peaks. The refractive index sensitivities of wavelength shift and loss change reach to as high as ?2,406.1 nm/RIU and ?156.8 dB/RIU, respectively. The sensor is insensitive to the refractive index change of liquid caused by environmental temperature. It can be used for liquid refractive index sensing with high sensitivity, especially for water pollution monitoring.     

Ultra-long-period fiber grating cascaded to a knob-taper for simultaneous measurement of strain and temperature

This study presents a simple Mach–Zehnder interferometer (MZI) to obtain the bimodal characteristics that realize simultaneous measurement of strain and temperature through cascading an ultra-long-period fiber grating and a knob-shaped taper. We obtain the multi-dip feature from the MZI, and the Dips 2 and 5 are selected from 11 interference dips. Experimental results indicated that the wavelength sensitivities of Dips 2 and 5 are ??0.54 nm mε^?1 and 0.058 nm °C^?1, and ??0.53 nm mε^?1 and 0.055 nm °C^?1 to strain and temperature, respectively. The depth sensitivities are ??3.3 dB mε^??1, ? 0.015 dB °C^?1 and ?5.8 dB mε^?1, and 0.06 dB °C^?1 for Dips 2 and 5, respectively. It is concluded that the proposed structure is suitable for simultaneous strain and temperature measurements.     

可双参量同时测量的光纤磁场传感器

设计并制作了一种马赫-曾德尔干涉仪(Mach-Zehnder Interferometer,MZI)与光纤布喇格光栅级联的光纤磁场传感器,其中MZI由相当于分光器的锥结构和相当于耦合器的花生锥结构级联组成,封装在填充了磁流体的毛细管中.由于磁流体的有效折射率会随着外界磁场强度的改变而变化,故可通过观察干涉谱的特征波长的变化来测量外界磁场强度,而光纤布喇格光栅透射峰对磁场强度不敏感.当磁场强度由0mT变化到20mT时,马赫-曾德尔干涉峰的灵敏度为0.11nm/mT.温度特性实验测得马赫-曾德尔干涉峰和光纤布喇格光栅透射峰的温度灵敏度分别为0.401 5nm/℃和0.011 4nm/℃.因此,可利用敏感矩阵实现双参量同时测量.     

埋入式F-P光纤应变传感器在混凝土桥梁健康监测中的应用研究

对基于白光干涉的埋入式F_P光纤应变传感器的测试原理及主要结构参数进行了分析,介绍了该埋入式传感器的研制工艺特点。通过对传感器的性能考核试验,验证了该传感器具有优良的精度稳定性和耐久性,通过秦沈客运专线辽河特大桥施工过程监测试验,验证了该传感器满足桥梁施工现场复杂状况下混凝土结构应变监测的要求。由于该传感器的成本不及同类型进口产品的1/5,具有广阔的普及应用前景。     

Single S-tapered fiber Mach-Zehnder interferometers

A fiber Mach-Zehnder interferometer (MZI) sensor, novel to our knowledge, based on a single "S"-like fiber taper has been fabricated via applying nonaxial pull in fiber tapering by a fusion splicer. The typical feature size of the structure has a length of 660 μm and the axial offset of 96 μm. This S fiber taper MZI has a refractive index (RI) sensitivity of 1590 nm/refractive index unit in the RI range of 1.409-1.425 and a strain sensitivity of about -60 pm/microstrain, which is 30 times higher than that of the normal two-taper-based MZI sensors.     

纤维光锥有效透过率的理论分析

光锥的有效透过率不仅影响光锥与CCD的耦合效率,而且会影响到耦合器件的信噪比.本文主要从理论上讨论了影响光锥有效透过率性能的因素,从纤维光学元件的实际内部结构推导出了其实际有效填充率,从光线在光锥中的传输特征推导出了光线在光锥中传播时产生的衰减损耗,最后提出了提高光锥有效透过率的方法和途径.     

Tapered Mach–Zehnder interferometer based on two mechanically induced long-period fiber gratings as refractive index sensor

A Mach–Zehnder interferometer formed in single mode fiber is implemented. The interferometer is built by two mechanically-induced long-period gratings. In addition, a fiber taper in the middle section is inserted. The spectral properties of the whole system are analyzed. Visibility of the interference fringes up to 0.80 (the higher ever reported using mechanically-induced long-period gratings) with fringe spacing in the 4.1 to 0.86 nm range are experimentally demonstrated. The proposed device allows reducing the fiber diameter of the section between gratings with a minimal effect in the interference fringe spacing. The sensitivity of the interferometer to external refractive index changes was also studied. It is experimentally shown that, due to the nature of the cladding mode excited, it is necessary to taper the fiber to improve the system sensitivity to external refractive index. Fiber tapers with different diameter, inserted between the long-period gratings pair were fabricated and tested for measuring external refractive index changes. A maximum resolution of 2.3×10^?4 RIU in a refractive index range from 1.36 to 1.402 is achieved.     

保偏光纤光栅应变传感器的研究

针对光纤布拉格光栅(FBG)温度和应变的交叉敏感问题,设计了一种带熔点保偏光纤光栅(PMFBG)结构。该结构通过将2段保偏光纤带加大推进量熔接,形成中间凸起结构,然后在熔点位置写入光栅。文中首先采用熊猫保偏光纤设计制作了该结构,并搭建实验装置测试其在(0~2)N轴向应力作用下的反射光谱,发现PMFBG快轴和慢轴的反射谱均分裂成2个峰值,随着轴向应力的增加,反射谱整体产生红移,同时分裂的2个峰值强度的比值单调减小,且不受温度的影响。随后,采用有限元法分析了该结构的轴向应变分布,并基于传输矩阵法仿真分析了该PMFBG反射光谱随应力的变化特性,仿真与实验结果的一致性较好。证实可利用PMFBG反射光谱的峰值之比消除轴向应变与温度的交叉敏感性,实现轴向应变的测量。     

Simultaneous strain and temperature measurement using a highly birefringence fiber loop mirror and a long-period grating written in a photonic crystal fiber

We present a new design for simultaneous strain and temperature measurement using a high-birefringence fiber loop mirror (HiBi-FLM) concatenated with a temperature-insensitive long-period grating (LPG) written in a photonic crystal fiber (PCF). The FLM acts as a sensor head, while the LPG in PCF serves as a filter to convert wavelength variation to optical power change. By measuring the wavelength variation and the power difference of two near peaks in the spectral response of this configuration, simultaneous strain and temperature measurement is obtained.