Research On Optical Fiber Sensing Technology Based On The Principle Of Online Machzente Interference

Fiber optic sensors are wildly used in the high precision measurement of physical parameters,healthy monitoring of buildings,perimeter security,etc.,owing to the advantages of high corrosion resistance,immunity to electromagnetic interference,low cost and ease of fabrication.Especially,in-line Mach-Zehnder interferometers?IMZI?,based on the mode coupling in fiber,have become a hot topic in fiber sensing and been applied in the sensing of physical and biochemical parameters due to their compactness and high sensitivity.To date,in order to enhance practicality,the studies of IMZI mainly focus the sensor with multiple functions,high single-to-noise output and crosstalk suppression.Then,the main work in this paper is as follows:?1?Theoretically and experimentally studied the IMZIs with fiber-core mismatch and offset.The temperature characteristics are tested for the fiber-core mismatched IMZI in the ranges of-40⁰?and 20-80?.Then,a novel composite interferometer is fabricated based on fiber-core mismatch method and multimode interference.The characteristics of temperature,strain and refractive index?RI?are extensively studied.According to the different RI responses?red-shift and blue-shift at different fringes?,the RI sensitivity can be double-improvement by the simple differential operation.?2?A thin-core-fiber based IMZI with small offset is proposed.The single modal interference and equal sensitivity of temperature at different wavelength are found.A high sensitivity consistency of temperature?⁰.996?is experimentally obtained and a novel dual-differential temperature compensation method is proposed to eliminate the temperature cross-talk in simultaneous measurement of curvature and strain,and the corresponding sensitivities are-1.92 pm/??and-17.67 nm/m^-1,respectively.?3?The active sensing experiment is performed to improve the detection resolution.The offsetted IMZI as a tunable bandpass filter is introduced to a fiber ring-cavity laser.A laser signal with high single-to-noise?42.76 dB?and narrow linewidth?0.1 nm?is realized.Futher,a fiber Bragg grating,free to the external RI,is introduced into the IMZI.By finely adjusting the variable optical attenuator,a dual-ring dual-wavelength laser sensor without cross-talk constructed for simultaneous measurement of temperature and RI.The experimental results show that the sesivitities of temperature and RI are 113.1pm/?and-30.57 nm/RIU,the detected resolution of temperature and RI are 0.105?and3.88×10^-4 RIU.