Research On Fabrication And Characterization Of Superimposed Long Period Photonic Crystal Fiber Grating

With the development of optical fiber technology in recent years,photonics crystal fiber?PCF?appears as a new type of optical fiber,which has many unique characteristics such as endless single-mode,adjustable mode field,highly nonlinear and so on.Optical fiber superimposed long period grating?SLPG?is a special grating which has a number of grating superimposed in the same area of optical fiber.This grating has unique mode conversion characteristics,which can be used to shape the spot and achieve the high sensitive measurement.With the unique properties and advantages,PCF and SLPG has shown great application prospects in the field of optical fiber communication and optical fiber sensing.The combination of the two is bound to induce much more new features,and further promote the development of fiber and grating technology,broaden the scope of application of fiber gratings.In this thesis,we study the mode coupling theory,the gate mechanism,the fabrication method and the characteristics of PCF superimposed long period grating.The main research work is as follows:Firstly,based on the coupling mode theory and coupling local mode theory,the coupling equations of PCF superimposed long period grating induced by different modulation perturbation are deduced respectively.Secondly,the preparation theory of PCF superimposed long period gratings induced by CO₂-laser was studied.The relationship between laser parameter,PCF temperature field and the deformation of PCF cross section has been researched with the thermal deformation theory.Based on this,the relationship between the deformation and the grating transmission spectrum has been studied.And by using the superimposed long period grating coupling mode theory,the relationgship between the grating parameter and grating spectrum has been studied.These provide a theoretical guidance for the fabrication of PCF superimposed long period grating.Thirdly,explore the fabrication method of PCF superimposed long period grating.The influence of laser scanning frequency,scanning speed and Q frequency to the PCF long period grating spectrum is studied experimentally.The influence of subsequent-grating to the PCF superimposed long period grating is analyzed,and the relationship of the angle between the two sub-gratings and the transmission spectrum is discussed.Finally,the temperature and strain response of PCF superimposed long period grating were analyzed experimentally,which establish the foundation for the application of grating in the field of sensing and communication.