Study On Novel Fiber Anemometer

Compared with conventional sensors, fiber-optic sensors possess lots ofirreplaceable advantages, such as integrated structure, high sensitivity, immunity toelectromagnetic interference, and potentially low cost. Due to these uniqueadvantages, fiber-optic sensors have been widely applied to various fields,including military, oil, electricity industry, engineering industry, biological andchemical industry, and medical industry. This work worked over fiber anemometer,mainly based on optical fiber optic sensing, fiber Bragg grating and fiber opticinterferometer technology. The main contents are as follows：1. The general situation fiber-optic sensors and its applications are introduced.Fiber grating fabrication and its classification are introduced. The fundamentalprinciple and sensing system based on FBGs are analyzed. As an importantapplication of fiber-optic sensors, the development of fiber anemometer is reviewed,which lays the foundation for study on fiber anemometer.2. A short multimode fiber （MMF） was spliced in just upstream of a uniformfiber Bragg grating. The short MMF section generates cladding modes in the fiberthat contains the FBG. Several of these modes get reflected back by the FBG atshorter wavelengths and re-enter the launch fiber after passing through the MMFsection. The net re-coupling efficiency between the incident forward core mode andreflected cladding modes is-20dB when the fiber is straight, but decays when acurvature applied on the sensing structure. A maximum sensitivity of0.74dB/m^-1isobtained in a large measurement range up to15.5m^-1with no orientationdependence of the sensitivity. The reflected coupled power variation is measured tobe±0.1dB over the temperature range from0to70oC allowing fortemperature-independent curvature measurements.3． A sensor head consisting of a photonic crystal fiber （PCF）-basedMach-Zehnder interferometer （MZI） and a fiber Bragg grating （FBG） is raised andexperimentally demonstrated for simultaneous measurement of curvature andtemperature. The MZI fabricated by splicing a short length of PCF between twosingle-mode fibers with the air-holes structure completely collapsed near the splicing points, is sensitive to fiber bending and surrounding temperature, while theFBG is only sensitive to the later. Simultaneous measurement of curvature andtemperature is therefore obtained. Sensitivities of4.06nm/m^-1and6.30pm/°C areachieved experimentally for curvature and temperature, respectively. And thecorresponding resolutions are5.2×10-4m^-1and1.25°C for curvature andtemperature, respectively, based on the wavelength measurement resolution of10pm.4．An optical fiber-optic thermal anemometer is proposed based on a silverfilm-coated fiber Bragg grating （FBG） assisted by a core offset fusion splice. Lightfrom a pump laser propagating along the fiber is coupled into the fiber cladding bythe splice and absorbed by the silver film to generate heat and increase thetemperature of the FBG. Air flow cools down the FBG and its velocity can bemeasured by the Bragg wavelength shift of the FBG. Experimental results showthat the proposed FBG thermal anemometer allows a high resolution of0.022m/sin a range up to6m/s.。...