【作者】 吴迪；

【导师】 赵勇；

【作者基本信息】 东北大学 ， 检测技术与自动化装置， 2018， 博士

【摘要】 磁场检测在很多领域都有重要的应用,例如军事,工业和电力系统传送等领域。与传统的电磁传感器相比,光纤磁场传感器由于其体积小、灵敏度高及抗电磁干扰等优点吸引了众多研究学者的关注。光子晶体光纤因其灵活的空气孔结构而具备很多独特的光学特性,也使其易于通过与敏感材料的结合实现传感的目的。磁流体作为一种新型的功能介质,它有许多磁光特性,如双折射特性、法拉第效应、场透射特性和可调折射率特性等,近年来,基于磁流体的光纤磁场传感器正不断涌现。本论文以光子晶体光纤为研究对象,以新型功能性材料磁流体作为传感介质,以探索新型光纤磁场传感器为主线,开展了基于磁流体和光子晶体光纤的磁场传感特性分析和实验研究,本文主要完成的工作和取得成果包含如下六个方面:(1)理论分析得出温度和磁场是影响磁流体的折射率的两大因素,设计一种具有独立传感探头的磁流体折射率测量方案,分别测试温度和磁场(强度和方向)对磁流体折射率的影响,结果表明磁流体的折射率与温度的升高呈反比,灵敏度为-8× 10-5/℃;随着磁场强度的增强,平行磁场下的磁流体的折射率与磁场强度成正比,垂直磁场条件下,磁流体的折射率与磁场强度成反比,磁流体折射率线性变化区间为100Gs-600Gs,灵敏度为4×10-5/Gs。为了更直观的解释上述磁流体的折射率特性,建立Monte Carlo模型,从微观结构的角度模拟磁性粒子在磁场作用下的运动规律。该特性为磁流体在光纤传感器中的应用提供了良好的理论基础。(2)利用有限元方法建立光子晶体光纤传输模型,理论研究占空比对光纤模式传输特性的影响;建立高双折射光子晶体光纤液体填充模型,分析不同的填充模式下HB-PCF的双折射特性,结果表明全填充的方式比选择性填充有更高的双折射灵敏度。(3)在实验研究基于磁流体和光子晶体光纤相结合的磁光器件时,克服了两大工艺难题。第一个是实现了单模光纤与填充了液体的光子晶体光纤的低损耗熔接,分析影响熔接效果的相关参数(放电时间,放电电流,放电中心偏移量,推进距离)后,利用控制变量法,在反复实验之后确定一组最佳熔接参数,需要注意的是,在液体填充到空气孔中后,要继续抽一小段空气以避免液体和光纤端面的直接接触。第二个是实现了利用熔接机拉制光子晶体光纤锥,对熔接机二次开发,自主编程实现锥形光纤的拉制,针对单模光纤和光子晶体光纤分别提出两种拉锥方案,经测试利用熔接机拉锥的方法具有很高的稳定性,可用于批量拉制光纤锥。这两大难题的解决为搭建实验系统提供了工艺保障。(4)在实验过程中完成了两个器件的制作,根据亥姆霍兹线圈的原理,制作一个带有循环液冷回路的磁场发生装置,可通过改变线圈内部电流实现磁场的匀强变化。另外在利用光纤锥实现液体检测的时候,制作了一个PDMS液体检测池,可有效地保护脆弱的锥区,并保证光路的稳定性。.(5)提出一种基于磁流体填充高双折射光子晶体光纤的Sagnac磁场传感模型,理论推导出其透射函数,将磁流体填充到高双折射光子晶体光纤的空气孔中,然后插入到Sagnac光纤环镜中,该方法将磁场的变化转化为磁流体折射率的变化,导致HB-PCF的双折射值发生变化,最终表现为干涉谱的移动,从谐振波长的变化可以反演出外界磁场的变化。折射率验证实验中,将酒精填充的HB-PCF的空气孔中,当外界温度改变时,谐振波长发生移动,灵敏度为0.8833nm/℃,证明了该结构的灵敏性。磁场测量实验中,灵敏度高达107.3pm/Gs。该传感器具有体积小,抗电磁干扰和灵敏度高等优点,具有广阔的市场应用前景。(6)提出了一种基于光子晶体光纤锥的M-Z折射率传感模型,由一段光子晶体光纤经过拉锥后熔接在两段单模光纤之间形成干涉结构,根据倏逝场理论可知锥区对折射率敏感,从理论上分析了该传感器的干涉原理后进行实验探究,先通过对不同折射率的氯化钠溶液验证该结构对折射率的敏感性,实验得出该折射率传感器的灵敏度高达51.902um/RIU,折射率的分辨力为1.93×10-5 RIU。将磁流体包裹在光子晶体光纤锥附近用毛细管封装好后做成磁流体传感探头,利用上述结构实现磁场传感,实验测得该传感器的波长灵敏度为3.32pm/Gs,分辨力达到0.3Gs。更多还原

【Abstract】 Magnetic field detection is essential in many fields,such as military,industrial and electric power transmission.Fiber-optic devices have attracted a variety of research interests due to their outstanding advantages over conventional electromagnetism sensors,including small size,high sensitivity,and immunity to electromagnetic interference.Photonic crystal fiber(PCF)exhibits unique optical properties owing to its flexible air hole structure,which are more natural for sensing purposes by incorporating with other sensitive materials.As a new kind of functional medium,magnetic fluid(MF)has versatile magneto-optic properties,for example,birefringence,Faraday Effect,field-dependent transmission,tunable refractive index and so on.In recent years,a wide range of optic-magnetic sensors based on magnetic fluid has emerged.In this thesis,the photonic crystal fiber as the research object,and the new functional materials magnetic fluid as sensing media were selected.The sensing characteristics and technologies of the magnetic field sensors based on PCF and MF were researched.The primary job and the achievement of the thesis include six aspects as follows:(1)Theoretical analysis shows that the refractive index of MF can be modulated by the temperature and the external magnetic field.In this thesis,a method based on Fresnel reflection at the fiber end face was presented.Experimental measurements were carried out to investigate the magnetic field(intensity and direction)and temperature-dependent refractive index of the MF.The effect of temperature on is relatively insignificant with the sensitivity of-8×10-5/℃.With the increase of the magnetic field intensity,the nMF increases gradually when H//Light,while decreases when H // Light.The effect of magnetic field on nMF is 4×10-5/Gs in the range of 100 to 600 Gs.Besides,the mechanism of refractive index modification was analyzed from the point of the microstructure by the Monte Carlo method.This feature provides a good theoretical basis for the application of magnetic fluid in fiber-optic sensors.(2)The transmission model of PCF was established by finite element method,and the effect of duty ratio on transmission characteristics was analyzed theoretically.The transmission model of HB-PCF with liquid filled was developed to analyze the birefringence of HB-PCF in different filling modes,in this thesis was selective filling and full filling.The results showed that it has a higher sensitivity of birefringence in full filling case than selective filling.(3)Two technical difficulties existed in the experimental study on magneto-optical devices based on magnetic fluid and PCF have been overcome.The first one is to realize the low loss fusion of SMF and the PCF filled with liquid.Several main parameters(arc_time,arc_power,arc center_offset and push_dist),which influence the welding quality were analyzed.After a large number of experiments,a set of optimal welding parameters was determined by control variable method.Note that,a little bit of air should continue to pump after the liquid was filled in the air holes.This avoids direct contact between liquid and PCF ends.The second is the realization of the PCF taper by the secondary development of a fusion machine.Two kinds of taper schemes are proposed for SMF and PCF,respectively.Test results indicated the program has significant stability.The solution of these two problems provided the technological guarantee for the establishment of the experimental system.(4)Two devices were produced during the experiment.According to the Helmholtz coils,a pair of coils with a circulating liquid cooling loop was made to generate the magnetic field.The magnetic field can be uniformly changed by changing the internal current of the coil.In addition,a PDMS detection cell was specially designed to protect the weak taper and increase the stability and robustness of the device.(5)A magnetic field sensor was proposed merging the advantages of both HB-PCF and magnetic fluid.A section of MF-filled HB-PCF was inserted in the Sagnac loop as the sensing element.The transmission function of the Sagnac interferometer was deduced theoretically.The refractive index of MF is changed by a tunable magnetic field,and the resonant dips wavelength produced by the Sagnac FLM drift correspondingly.Therefore,the magnetic field intensity is obtained by the wavelength drift of the resonant dip in the Sagnac interferometer.In the refractive index verification experiment,ethanol was filled in the air holes of HB-PCF.The resonant wavelength shifts when the external temperature changes.The RI sensitivity of 0.8833nm/℃ was obtained.Through the experiment,the sensitivity of the structure was proved.In the magnetic field measurement,the sensitivity was as high as 107.3 pm/Gs.The sensor in preference to other sensors has small volume,anti-electromagnetic interference,and high sensitivity,thus enjoying a broad prospect of market application.(6)A compact and robust refractive index(RI)sensor based on a tapered photonic crystal fiber(PCF)Mach-Zehnder interferometer was proposed.It consists of a section of tapered PCF which is spliced between two single-mode fibers(SMF).A strong evanescent field was formed near the tapered region and made it susceptible to external RI variations.The interference was utilized between core modes and cladding modes of the PCF.Experimentally,the sensor exhibits highly RI sensitivity which is found to be 51.902nm/RIU within a range from 1.3411 to 1.3737.A resolution of 1.93×10-5 RIU was achieved since the OSA has a resolution of 1 pm.The temperature effect of the sensor is also analyzed.The magnetic fluid is filled in the capillary to coat the PCF taper and sealed by UV glue at both sides to avoid the magnetic fluid from leaking out.Based on the theoretical and experimental results,the sensitivity of magnetic field intensity 3.32 pm/Gs was proved.The Resolution reached 0.3Gs.更多还原