Research On Strain And Temperature Sensing Technology Of Optical Fiber Air Microcavity

The optical fiber air micro-cavity is an infiber air-cavity based on Fabry-Perot interferometer,which can be used in measurement situations of refractive index,temperature,strain,humidity,electromagnetic field and so on.Because of simple preparation method,low manufacturing cost,excellent sensing properties and single probe head type structure,so the optical fiber micro-cavity has not only high research value but also broad application prospects.However,the micro-cavity structure need to be enriched to meet the needs of different occasions because of the relatively simple structures and limited application field.Although the traditional theory and simulation of fiber optic micro-cavity are mature,they all need to advance with the design diversification.This thesis mainly completes the following six contents.(1)In the first chapter,the fabrication methods of fiber micro-cavity are summarized,and the fiber fusion method and the polymer composite method are research emphasis in this paper.The applications of optical fiber micro-cavity are summarized,and the strain sensing and temperature sensing are research emphasis in this paper.The above work provides the basis for the following work.(2)In the second chapter,the parallel plate multi-beam interference theory and double beam theory of optical fiber micro-cavity are first elaborated,and the temperature and strain sensing principle of fiber micro-cavity are derived in this paper.Secondly,the FDTD and the optical simulation design based on RSOFT are introduced in detail,and the FEM and the thermodynamic simulation based on COMSOL are introduced in detail.At last,the hourglass shaped optical fiber micro-cavity is optimal analyzed based on the combination of RSOFT and COMSOL.(3)In the third chapter,an all fiber rectangular micro-cavity axial strain sensor is designed based on fused silica capillary method.The spectral properties and strain sensitivity of fiber rectangular micro-cavities with different cavity lengths are analyzed and compared.Optical fiber rectangular micro-cavity is the most simple fiber micro-cavity structure,and is the design basis of complex optical fiber micro-cavity.The research shows that the structure has the characteristics of temperature cross insensitivity.(4)In the fourth chapter,an all optical fiber micro-cavity sensor that realizing simultaneous measurement of curvature and refractive index is designed.A fiber taper is made on one side of the rectangular micro-cavity to realize bending measurement,and the third optical fiber end face is fabricated on the other side of the rectangular micro-cavity to realize refractive index measurement.The study shows that the upper envelope curve of interference spectrum can demodulate the curvature,the lower envelope of interference spectrum can demodulate the refractive index,and this fiber sensor also has the temperature cross insensitivity characteristic.(5)In the fifth chapter,a piston type optical fiber micro-cavity sensor is designed,which is made of two single mode optical fibers embedded in a large diameter capillary glass tube.The spectral characteristics and temperature sensitivity of piston type optical fiber micro-cavity with different cavity lengthes based on UV is compared in experiment.And the temperature sensitivity of this structure is improved to above 6nm/℃ by composite material enhancement.(6)In the sixth chapter,a fiber air micro-cavity structure based on liquid silicone oil is designed.The overall size of this structure can be controlled within 100p,m,which can realize the true probe sensing.The experimental results show that the temperature sensitivity of this sensor is about-1.6nm/℃ in the range of 25℃-65℃.Silicone oil is a non-toxic and harmless material,which has high biological affinity,so this sensor has a broad prospect in the field of biochemistry.Based on the achievements of predecessor,the finite element method(FEM)and finite difference time domain method(FDTD)are used to further improve the simulation model of fiber micro-cavity structure,and four different optical fiber micro-cavity sensors are designed for strain measurement and temperature measurement in this paper.