Research On Flexible Optical Fiber Sensing Structure

All fiber Mach Zehnder interferometer(MZI)is a kind of all fiber interference structure,which has the advantages of simple structure,good device integration,high measurement accuracy and low cost.Flexible sensor is a kind of sensor made of flexible material,which has good flexibility,ductility and even free bending.In this paper,MZI,which is composed of single-mode fiber(SMF)-thin core fiber(TCF)-Single-mode(STS),is used as the basic structure,and PDMS is selected as the packaging material to develop a kind of optical fiber flexible sensor.Through the combination of theoretical and experimental research,the sensing characteristics of this kind of sensing structure are studied.The main work is as follows:1.The development of flexible sensors at home and abroad is reviewed.In this paper,the development status,advantages and disadvantages of four main types of flexible sensors at home and abroad are reviewed.The basic principle and development of fiber-optic flexible sensors are emphatically introduced.The advantages of fiber-optic flexible sensors in performance and application environment are analyzed.2.Based on the analysis of the sensing principle of all optical fiber MZI structure,an all optical fiber MZI sensing structure based on STS core mismatch structure is proposed,and its strain and temperature characteristics are studied theoretically.A kind of optical fiber flexible sensor is developed and designed by ourselves.Aiming at the problem of STS's embedding position,the finite element simulation of PDMS is carried out,and the strain distribution and the best embedding position of the sensor are obtained.3.Experimental study on pressure sensing of optical fiber flexible sensor.The working principle,structure and fabrication method of the sensor are analyzed in detail,and the pressure sensor experiment is carried out.The experimental results show that the interference wavelength of the sensor moves to the long wave direction with the increase of pressure,and the pressure sensitivity is 0.417nm/N.At the same time,a flexible pressure sensor based on STS dislocation fusion structure is designed and manufactured.The experimental results show that the pressure sensitivity of the sensor is 0.833nm/N,which is twice higher than the previous structure.4.Experimental study on temperature sensing characteristics of optical fiber flexible sensor.The temperature rise and the temperature drop of the sensor are studied.In the temperature rising experiment,with the increase of temperature,the interference wavelength moves to the long wave direction,while in the temperature dropping experiment,with the decrease of temperature,the interference wavelength moves to the short wave direction,which is consistent with the temperature sensing theory of the sensor.The experimental results show that in the temperature range of 30? to 100?,the temperature sensitivity of the flexible sensor is 96.1pm/?,and that of the flexible sensor is 97.4pm/?.5.The optical fiber flexible sensor is used in the experimental research of object shape recognition.Combining the sensor with the neural network pattern recognition of MATLAB,the experimental research of object shape recognition is carried out,and an app which can visualize the recognition results is made.The experimental results show that the accuracy of the training results is 100%in the recognition of straight line and circular arc.In the same way,the accuracy of training results is 100%in the training recognition of 45° and 90°,45°and 75°,45° and 60°.An app is made to visualize the results of object shape recognition,which makes data processing more convenient and fast.The results and accuracy of object shape recognition can be viewed only through simple operation.