Research On Interferometric Sensor Based On Spherical Optical Fiber Coupled Structure

Optical fiber sensors as a new kind of sensor which just have experienced several decades from their emergence to widespread application,has gradually become mature in theoretical and experimental aspects.Interferometric fiber optic sensor have been extensively investigated and researched in aviation and space,medicine,bridge detection due to its advantages of high sensitivity,low cost of fabrication,fitting for hard conditions.In this paper,under the premise of previous research work of our research group,novel fiber sensors based on multi-mode fiber(MMF)and spherical-shape structure have been designed and fabricated,and they can achieve measurement of the external parameters: temperature,refractive index and magnetic field.1.A sensing structure based on multi-mode fiber(MMF)and spherical-shape structure is designed to measure the external parameters.The transmission spectrum of the novel composite structure is superposition of a series of interference.The measured temperature sensitivities are 0.053nm/? and 0.043nm/?,refractive index sensitivities are-41.51nm/RIU and-59.19nm/RIU,magnetic field sensing sensitivities are 0.047nm/mT and 0.077nm/mT,respectively.2.A sensing structure based on concatenated core-offset and spherical-shape structure is proposed to measure the external parameters.The incident light is divided into two parts through the core-offset structure of the sensor,not only the high order core mode is excited,but also the different order cladding modes are inspired.The experimentally measured temperature sensitivities are 0.042nm/? and 0.059nm/?,refractive index sensitivities are-46.12nm/RIU and-54.17nm/RIU,magnetic field sensing sensitivities are-0.187nm/mT and-0.11nm/mT,respectively.3.A fiber sensor based on few-mode fiber and spherical-shape structure is designed.Different from the multimode fiber,the numbers of modes participating in interference are less in the few-mode fiber and the energy ratio of high order mode is higher.Therefore,the good effect of filtering mode can realize the optimization of sensing structure.The interference spectrum between certain high core mode and different order cladding modes of the few-mode fiber is used to measure the external parameters.The measured temperature sensitivities are 0.059nm/? and 0.05nm/?,refractive index sensitivities are-39.15nm/RIU and-48.82nm/RIU,magnetic field sensing sensitivities are-0.090nm/mT and-0.122nm/mT respectively.