Research On Novel Fiber Micro-cavity Based Sensors

"The Internet of Things"(IOT)is the third world developed wave following computer and internet industry.Advanced and reliable sensing technology is the pivotal basics for constructing IOT system.Fiber sensing is one of the most important part of sensing technology whose market share gradually increased due to its advantages of compact size,low loss,electromagnetic immunity,easy networking and long distance sensing.It is worth noting that reflection-type interferometric sensors had been attacted lots of researchers' attention and became an optimal solution in some occasions with limit space because of its smaller compact size,higher sensitivity and more convenient installation compare with other fiber sensors.The object of this research is the novel reflection-type interferometric sensors based on optical fiber microcavity and its demodulation technology.The aim of this study is to explore the potential of the optical fiber microcavity based sensors in the pratical application,and to realize lower crosstalk or multi-parameter measurement by special design of sensor or novel demodulation algorithm.Firstly,the research background,market share and development of optical fiber sensing technology and the importance of the reflection-type interferometric fiber sensors was briefly introduced.Then the classification,application and basic principle of Fabry-Perot optical fiber micro cavity based sensor are also introduced.An open-cavity fiber-optic Fabry-Perot interferometer,with a particular consideration for microfluidic refractive index sensing was proposed in the first chapter.The FPI is composed of an etched side-hole fiber(SHF)sandwiched between two single-mode-fibers.Chemical etching method is used to open up the cavity in the SHF.Experimental results show that an optimal RI sensitivity of more than 1251 nm/RIU and the temperature sensitivity can reach an ultralow level of 1.1pm/?.We also study the incoporation of the open-cavity based fiber sensor and the fiber bragg grating and realize a dual-parameter fiber sensor.Secondly an open-cavity based fiber humidity and temperature sensor which has a thin PVA film coated inside the cavity was designed.Sensing principle had been theoretically studied and the experiment results show that the humidity sensitivity,temperature sensitivity and response time are-1.2 dB/%RH,6.14pm/? and 660 ms respectively.Lastly a new elastic fiber micro-cavity based sensing structure was proposed.The sensor has a relatively higer sensitivity for surrounding acoustic vibration,strain and displacement owing to employing polydimethylsiloxane(PDMS)with low Young modulus as the 'soft splicing' material.We firstly desgin a acoustic vibration sensor without extra vibration transduced component and the sensing frequency range had been theoretically and experimentally verified cover at least from 200 Hz to 100 KHz and the sound pressure sensitivity at 200 Hz is 0.088 mV/mPa.Then,a sensitivity enhanced AC magnetic field fiber sensor was achieved by installed the elastic fiber micro-cavity on a magnetostrictive rod and a new demodulation method is also proposed to eliminate the temperature crosstalk.