Research On Optical Microifber Taper Sensor

With the technology and process level of fiber sensor improved, opticalfiber sensor is now entering a period of rapid development. Many countrieshave put great emphasis on the research and development of optical fibersensors. As it has the advantages of a small size, light weight, easy to bend,the nature of the insulation, anti-electromagnetic interference, resistance tochemical corrosion and other characteristics, optical fiber sensor isparticularly suitable for many applications on the occasions of narrow space,high temperature and pressure, explosive, chemical corrosion, strongelectromagnetic interference and other adverse environmental conditions,which is extremely difficult for the traditional electronic sensors to play theirrole.The optical microfiber taper studied in this paper is a double tapered fibertaper whose taper waist diameter is only a few microns. The fabricationprocess was very simple, just use the fusion splicer to stretch a standardtelecom single-mode fiber. In the fiber tapering process, a certain additionaltension was applied manually on one side of the fiber sample, leading to thestructure of significant axial asymmetric morphology. This structure canindependently form fiber modal interferometer in which both tapered sides ofthe mutation can make cladding mode and core mode coupling occur, andthen form a certain phase after they go through an intermediate tapered waist,generating the interference output ultimately. Compared to the normal scalefiber taper, the unique advantages of this taper is that the fiber evanescentfield will be a large part of the divergence to the outside environment as thetaper waist diameter reduces greatly, thus, the optical fiber sensingcharacteristics will be significantly affected by the external environment, andthis kind of optical microfiber taper will have a higher refractive indexsensitivity. From the data measured in the experiment, the highest refractive index sensitivity could be up to18989nm/RIU during the refractive indexrange of1.3955-1.4008, meanwhile, its asymmetry was also researched indetail to verify the fact that the asymmetry of optical microfiber taper has noeffect to sensing properties.On the other hand, significantly reduced diameter of the taper waist isalso more susceptible to axial stress in the fiber, thus optical microfiber taperwill have a relatively high stress sensitivity. Based on the sensitive nature ofthe refractive index and stress, we have had its packaged in the capillary byusing isopropanol and AB glue at a temperature range of20℃-50℃andgained a fiber temperature sensor of its highest sensitivity up to-3.88nm/℃.The sensing mechanism was also considered, that the thermo-optic effect ofsealed fluid, the thermal expansion effect of AB glue and the hydraulic effectsof fluid thermal expansion generated all have contributed to the ultra-sensitivetemperature response characteristics. In addition, we have also designedbutanol packaging and PDMS package type temperature sensor, and thehighest sensitivity observed were measured about-3.78nm/℃,-2.55nm/℃respectively. It has bright prospects for the smartly designed fibertemperature sensor which has the excellent properties of simple structure,economical cost, high sensitivity, and so on.