Side-hole Fiber Grating Fabrication Methods And Lateral Force Sensing Characteristics

With the rapid development of science and technology,the advent of artificial intelligence in the Internet of Everything in the 5G era,the Internet of Things sensing technology has been vigorously promoted,and fiber optic sensing technology has been paid more and more attention.Since the advent of fiber gratings,there have been more and more preparation methods in the past few decades.For fiber Bragg gratings,the preparation methods include:double beam interference method,phase mask method,femtosecond laser point-by-line method,etc.Gratings are more and more widely used as sensors for sensitive devices.This paper proposes the preparation of Fiber Bragg Grating(FBG)on special optical fiber and uses it as a sensor to detect the lateral force of the external environment.Its preparation technology,demodulation method,lateral force sensing characteristics and temperature and force cross sensitivity In-depth research on the characteristics,the main research work is as follows:1.Theoretical research on the sensing principle of birefringence fiber Bragg grating to measure lateral force.Based on the coupling theory of fiber Bragg grating,the elastic-optic coefficient of fiber Bragg grating is deduced,the principle of birefringence of fiber Bragg grating is known,and the theory of lateral pressure of fiber Bragg grating is analyzed,so as to know that under the action of external lateral pressure spectral characteristics of FBG and the changing law of birefringence.2.The fiber Bragg grating with side-hole fiber was prepared by using an ultraviolet laser phase mask.First,based on the structural parameters of the selected side-hole fiber,based on the Comsol simulation,the basic properties of the side-hole fiber were obtained,and the characteristics of its low-mode transmission were found;then,the fusion parameters of the side-hole fiber and the ordinary single-mode fiber were explored;then,The side-hole fiber Bragg grating was prepared by using the ultraviolet laser phase mask method,which mainly includes:fiber hydrogen-carrying sensitization,micro-calibrating the fiber direction,building a preparation system for the side-hole fiber grating,and using this system to prepare the side-hole fiber grating.3.The lateral force sensing characteristics of the side-hole fiber grating are studied theoretically and experimentally.First,design and build a lateral force sensing test system,which mainly includes:a pressure gauge,a pair of lifting platforms,and electric rotating fixtures;then,a polarization analysis system is used to demodulate the polarization-dependent transmission spectrum.This polarization analysis system mainly includes:Tunable laser,polarization analyzer N7786B and the optical power meter used with it;finite element simulation analysis of the side-hole fiber grating under lateral force load;then,the experimental study of the lateral force sensing characteristics of the side-hole fiber grating,It was found that when the external lateral force is applied to the side-hole fiber,the TE and TM spectra of the two modes corresponding to the side-hole fiber grating change,and the response of the side-hole fiber grating to external force has obvious directionality,when the force is along the side-hole fiber.The response of the fiber is greatest when it is applied in the slow axis direction.The birefringence introduced when the force is applied to 35N is5.48*10^-4.The response is the smallest when the force is applied along the fast axis direction of the side-hole fiber.It is introduced when the force is applied to 35N the birefringence is2.49*10^-4.The maximum value of the birefringent lateral force sensitivity of the side-hole fiber grating is S_B=0.1366/N,and the minimum value is S_B=0.0497/N,which is higher than the birefringent lateral force sensitivity of the ordinary single-mode fiber grating S_B=0.0374/N.When the two air holes of the side-hole fiber are subjected to lateral force from the outside,the stress will be more concentrated on the core,resulting in greater birefringence.4.The experimental study of the temperature and force cross-sensitivity of the side-hole fiber grating.Using the above polarization analysis system combined with a temperature furnace to test the temperature of the side-hole fiber grating,and using the birefringence test method to demodulate,the birefringence sensitivity of the side-hole fiber grating to the outside temperature is S_B=1.29*10^-8/?.This eliminates the crosstalk introduced by the temperature of the side-hole fiber Bragg grating force sensor when testing the external force.