Fabrication And Research On Sensing Characteristics Of Superstructure Microfiber Grating

Compared with the traditional optical fiber,the outstanding feature of the microfiber alies on its large evanescent field.Based on this characteristic,the microfiber have been developed to various sensitive sensors.On the other hand,fiber gratings have been widely used as optical fiber filters and sensors due to its good wavelength selectivity.In recent years,microfiber grating-based sensors have attracted much attention.In this thesis,we propose a kind of superstructuremicrofiber grating(SMFG)that integrates Bragg grating and long period grating for the first time,and study its sensing characteristics as well.This thesis includes the study of fabrication and spectral characteristics of the superstructure microfiber gratings,and systematically analysis of the sensing characteristics(temperature,strain,and refractive index),and proposes the use of a single grating for dual parameter measurement possibility.The full thesis mainly includes the following(1)The development trends and main characteristics of microfiber gratings are summarized,and the research status and development trends of superstructure fiber gratings are analyzed and summarized.The research background and significance of superstructure microfiber grating are described.The transmission theory of microfiber and the electric field distribution and energy distribution characteristics of evanescent field are analyzed.The coupling theory and spectral characteristics for fiber Bragg grating and long period grating are analyzed.The characteristics of superstructure fib er grating are studied,and the refractive index change characteristics and spectral characteristics under different sampling methods are summarized(2)We propose and demonstrate the fabrication of superstructure microfiber grating.First,a Bragg grating is written on a microfiber using ultraviolet lithography.Secondly,the surface of the microfiber with the Bragg grating is engraved by point-to-point method using femtosecond laser etching technology,which produces a periodic groove structure and forms a long-period grating The fabricated superstructure grating has shown the characteristics of both the Bragg grating and the long period grating.The spectral characteristics of the grow curves have been demonstrated Unlike traditional conventional optical fiber superstructure gratings,no multi-peak phenomenon appears in the reflection spectrum(3)The sensing characteristics of the superstructure microfiber gratings to the changes of the external environment are investigated.Due to the different mode coupling characteristics,the Bragg grating structure and the long period grating structure in the superstructure grating have different response to external parameters.The sensitivities of the microfiber Bragg grating and the long-period microfiber grating to simultaneous temperature sensing are 8.03 pm/? and 10.33 pm/?,respectively,the sensitivities to axial strain are 1.2 pm/?? and-1.8 pm/??,respectively,and the sensitivities to refractive index are 3.61 nm/RIU and 1534.78 nm/RIU,respectively.Though the different response of the reflection spectrum and transmission spectrum of the superstructure microfiber grating to the changes of the external parameters,the dual parameters can be measured simultaneously.