Research And Sensing Application Of The Novel Fiber Loop Mirror With Tail Probe

Compared with other sensors, interferometric fiber-optic sensor has the advantage of high sensitivity since it can detect changes in length which are equivalent to the magnitude of optical wavelength. As one interferometric sensor, fiber loop mirror (FLM) has received much attention recently due to its simple structure and easily tuned spectrum. However, FLM is always formed as the close loop with transmission path. So the sensing device is dependent of the loop, making it difficult for remote measurement. The output is also easily influenced as the extra phase difference is introduced by the disturbance within the loop. Moreover, fibers located on both sides of the sensing device in the transmission path will introduce more loss and disturbance.In this thesis, the optical path is improved by the open loop with tail reflection probe. The improved structures not only keep the advantage of FLM sensors, but overcome the limitations of FLM, so the application of FLM is extended.There are five main parts in this article, which are shown as follows:(1)In the first part, researches of interferometric fiber optic sensor are introduced first, and then typical FLM structures and sensors in recent six years are summarized in detail. All the above work provides ideas for the design of novel FLM.(2) In the second part, polarization light phenomenon in the fiber is described, the structure of FLM is analyzed, and the theoretical model of high-birefringence (Hi-Bi) FLM is established. Based on the above analyses, two novel FLMs with tail probe, namely FLM with Hi-Bi fiber in loop and with SMF-tail-probe (A type for short) and FLM with SMF in loop and with Hi-Bi-fiber-tail-probe (B type for short), are respectively proposed and theoretical models are established respectively, then the formulas of both output spectra are calculated respectively, finally the parameters of both output spectra formulas are simulated respectively.(3)In the third part, the experimental setups of output spectra based on the simulation results of both novel FLMs are developed respectively, which respectively include the general design of the setup, remote control of the spectrometer by PC and data acquisition and processing by PC. Finally, comparative analyses are made between the experimental results and the simulated results in both novel FLMs respectively. Therefore, the spectral features of both novel FLMs are grasped completely, which provide the basis for the sensing application of FLM.(4)In the fourth part, based on B type FLM, the temperature experiment is carried out, including the design of system, data processing and temperature calculation by PC. Temperature results are analyzed, relevant features are discussed, and problems need to be paid attention to in the experiment are explained. Finally, Comparison of temperature measurement is made between the Hi-Bi FLM and B type FLM.(5) In the fifth part, based on the FLM with Hi-Bi reflection probe, the reflection structure is replaced by the sucrose solution with variable reflectivity. The refractive index experiment is carried out, including the design of system, analysis of signal demodulation, introduction of signal demodulation circuit and data acquisition and processing by PC. Finally, refractive index results are analyzed, relevant features are discussed, and problems need to be paid attention to in the experiment are explained.