Research On Interferometric Fiber Optic Sensor Based On Butterfly Cone Structur

In recent decades,optical communication and sensing technology have developed rapidly,Fiber sensor stands out as a result of its high transmission efficiency,compact structure and strong anti-interference ability.It is becoming more and more mature in theoretical research and daily application.At present,it is widely used in medical detection,space technology,civil engineering,smart home and other fields.Various chemical and physical quantities,such as refractive index(RI),magnetic field,strain,ion concentration and temperature,can be detected by optical fiber sensors.At present,the construction of various new sensing structures on optical fiber to meet the measurement needs of different external conditions has been widely studied.In this paper,two types of interferometric optical fiber sensors are fabricated based on the new structure of bowknot type taper,and the sensing structure is analyzed in detail and studied theoretically.The pressure,refractive index and salt solution concentration are measured through experiments.The main research work is as follows:1.An optical fiber pressure sensor based on the cascade of bowknot type taper and spherical structure is fabricated.The bowknot type taper is used as the mode excitation structure,and the spherical structure is used for mode coupling,so as to realize the interference between modes.The pressure and temperature sensing experiments of the proposed sensor are conducted,which the pressure and temperature sensing are realized by monitoring the deviation of the spectrum.The experimental results indicate that when the pressure changes from 0 N to 1.2 N,the pressure sensitivity can reach up to 1.89464 nm/N;In the temperature range of 35℃-75℃,the maximum temperature sensitivity is 0.2014nm/℃.2.An optical fiber refractive index sensor based on bowknot type taper and core offset connecting of single-mode fiber is fabricated.The bowknot type taper is used as the mode excitation structure,and the core offset connecting position is used for mode coupling,so as to achieve the purpose of mode interference.The refractive index and temperature sensing experiments of the proposed sensor are carried out,the response of the sensor to different environments is analyzed by monitoring the deviation of the spectrum.the experimental results indicate that when the RI changes from 1.335 to 1.3552,the refractive index sensitivity is up to-107.21802 nm/RIU;In the temperature range of 35℃-75℃,the temperature sensitivity is up to 0.103 nm/℃.Which is still based on the sensing structure of bowknot type taper and core offset connecting of single-mode fiber,a polyimide film is coated on the surface of the sensing structure as the sensitive film of saline solution concentration.The salinity and temperature sensing experiment are carried out on the sensor,and the salinity and temperature sensing are realized by monitoring the deviation of spectrum.The experimental results show that the sensitivity is up to 0.2635 nm /% in the concentration range of 3.3%-20.1% salt solution;In the temperature range of 35℃-75℃,the maximum temperature sensitivity is 0.19957 nm/℃.