Research On Long-sensing-cavity Strain Sensor Based On Optical Fiber Fabry-perot Interferometer With HCF-SMF Structure

With the rapid development of urbanization and industrialization,the health monitoring of structures is particularly important.As a physical quantity that characterizes the degree of deformation of the structure,strain is essential to reflect the health status of the structure.Therefore,strain sensing is widely applied in the field of aerospace science and technology,aviation industry,deep sea exploration,weapons industry,petroleum and petrochemical,national large-scale construction,etc.Compared with the traditional strain sensing technology,fiber-optic strain sensing technology have been widely studied and applied owing to their unique advantages of immunity to electromagnetic interference,compact size and long-range transmission.However,the current common types of fiber strain sensors such as the FBG sensors are not able to meet the measurement requirements when the distribution of strain is very large.In view of this circumstance,an F-P sensor based on HCF-SMF structure with long sensing cavity for strain measurement has been proposed and demonstrated in this paper.The sensing principle and performance of the strain sensor has been theoretically and experimentally analyzed.The specific research works carried out in this paper are as follows:1.The basic principle of fiber-optic Fabry-Perot sensor has been analyzed,and the spectral characteristics of the fiber-optic Fabry-Perot sensor has been analyzed in detail.Aiming at the measurement for the strain with a relatively wide spatial distribution,an F-P sensor based on HCF-SMF structure with long sensing cavity for strain measurement has been proposed.The method of manufacturing the sensor is introduced.The effects of different welding parameters,end face reflectivity and hollow fiber length on the interference fringe contrast are analyzed,respectively.The strain transmission of the sensor is analyzed in detail.2.Aiming at the strain sensor proposed in this paper,the strain sensing model of the sensor is constructed,the temperature influence characteristic on the sensor is analyzed,and the strain-temperature coupling model is constructed to analyze the cavity length and the refractive index of the sensor influenced by strain and temperature changes.The fast Fourier transformation method and spectral peak tracing method are combined to demodulate the collected spectral information.3.The experimental system suitable for the strain sensing of the sensor proposed has been constructed.Two strain sensors with the sensing 10.05 mm and49.03 mm respectively are used to carry out the experiment.Under the condition of constant temperature,the strain sensitivity of two sensors both increase with the increase of the strain and the strain sensitivity of the sensor is enhanced from 20.42nm/?? to 115.57 nm/?? while the cavity length is increased from ?10mm to ?49mm,and the sensors have good repeatability.Meanwhile,the cross-effect of the temperature change on the strain characteristics of the sensor has also been experimentally analyzed,and the temperature compensation for the sensor proposed is realized with the help of FBG.