Research And Application Of Reflective LPFG Filter

Fiber optical filter is an important optical passive component.Fiber grating-based filter has advantages of compactness and low insertion loss,which is widely used in the field of optical communication and optical fiber sensing.Among them,LPFG type filter is one of fastest developing fiber filter in recent years.Different with FBG type filter,the LPFG fiber filter is one of transmission type filter,in order to realize its reflection filtering,this thesis take several different type of reflective LPFG filters into research,which is applied in the field of optical fiber sensing.The reflective LPFG is studied in this thesis firstly.In order to establish the theoretical model of reflective LPFG,simulating the optical structure of reflective LPFG by the way of finite element(FEM)at first,then the system of reflective LPFG filter is simulated by Optisystem software,and the filter characteristic is obtained.To further study the working principle of reflective LPFG filtering,the formula method and the beam propagation method(BPM)is adopted into the transmission characteristics calculation of reflective LPFG.Then the three different surface structure(core layer reflection,cladding layer reflection and surface total reflection)reflective LPFG is studied.In the field of sensing applications,the reflective LPFG band-rejection filter is applied into detection of solution concentration,when the solution concentration range from 0%to 90%,the solution concentration measured sensitivity is about-0.01389nm/%.Moreover,the structure of end face total reflection is studied in this thesis,and the reflective LPFG type of interferometer is a kind of Michelson interferometer,which is composed of LPFG and reflector.This thesis proposed a reflective MLPFG interferometer based on double cladding fiber,the MLPFG and reflector is fabricated by spring force induced and method of electroless silver coating.In order to achieve accurate measurement in liquid level sensing by reflection type of optical fiber interferometer,through theoretical and experimental analysis of the interference characteristics.By selecting the appropriate parameters for the liquid level sensor,when the MLPFG is stressed at 20N,and the coherence length is 38cm,the resulting sensing sensitivity reached at 0.03244nm/mm,the correlation coefficient of wavelength and liquid level is 0.98604,compared with the traditional reflective interferometer has a higher sensitivity.In addition,the device also has the advantages of low cost,multi parameters adjustable,repeatable,etc.,and there is still a lot of room for development in the fields of sensing and optical communication.