Research On Double-cladding Fiber Multiparameter Sensor With Waist-enlarged Taper Structure Cascade LPFG

In recent years,optical fiber sensors have gradually been used in various fields of production and life due to their unique advantages.But in the process of sensor measurement,the cross-sensitivity to be measured will lead to inaccurate measurement.Multi-parameter measurement can be achieved by improving the optical fiber and its sensor structure,and the cross-sensitivity problem can be well improved,which has attracted widespread attention from domestic and foreign scholars.Therefore,multi-parametric sensors based on waist-enlarged taper structure cascaded long period fiber gratings with double-cladding fiber have different sensitivity to parametric quantities due to each valley of the wave.Demodulated the coefficient sensitivity matrix,multiple parameters can be measured simultaneously,which is of great research significance.This article summarizes and introduces the common types of optical fiber multi-parameter sensing devices and the current research status at home and abroad.On this basis,three sensing structures are designed,including:Firstly,the transmission mode and transmission spectrum of double-cladding fiber and long-period fiber grating are analyzed by the coupled mode theory,and the principle of intermode interference and the demodulation method of multiple parameter measurement are studied.Secondly,the preparation method of a single waist-enlarged taper structure cascaded LPFGs with DCF multi-parameter sensor is studied.The influence of the length of the double-cladding fiber and the size of waist-enlarged taper on the transmission spectrum is analyzed,and the temperature,refractive index,and axial strain are theoretically analyzed.The three parametric measurement platforms were built for the sensing experiments,and the repeatability was measured respectively.The transmission spectrum and sensitivity of the sensor are simulated.The three parameters can be measured simultaneously by means of the coefficient sensitivity matrix.Then,the preparation method of dumbbell I type DCF multi-parameter sensor is studied.The measurement platform of temperature,refractive index and axial strain is set up for sensing experiments,and repeated measurements are carried out respectively.The transmission spectrum and sensitivity of the sensor are simulated.Simultaneous measurement of three parameters is achieved.Finally,the preparation method of dumbbell II DCF multi-parameter sensor is studied,and the influence of taper and taper length on transmission spectrum is analyzed,and the temperature,refractive index and axial strain measurement platform is built.The sensing experiment is carried out,and the repeatability measurement is carried out respectively.The transmission spectrum and sensitivity of the sensor are simulated.Simultaneous measurement of three parameters is achieved.