Research On Characteristics,fabrication And Applications Of Tilted Fiber Bragg Gratings

Fiber Bragg gratings(FBG)is one kind of important passive fiber components,and has various applications in optical fiber communications,optical fiber sensors,fiber lasers,etc.As a special kind of FBGs,tilted fiber Bragg gratings(TFBG)have tilted grating planes that enhances the coupling of light from the core mode to backward propagating cladding modes,resulting in good performance in optical fiber sensing,optical filtering,etc.This article focuses on the characteristics,fabrication and applications of TFBG,and its main content includes the following aspects:(1)The histories,classifications and fabrication techniques of FBG are simply introduced firstly.Then,the theories,fabrication techniques,and applications of TFBG are emphatically introduced.The idea of using chirped TFBG as a filter to suppress the stimulated Raman scaterring in fiber lasers is proposed to potentially enhance the total output fiber laser power.(2)Based on coupled mode theories,the modes coupling in both FBG and TFBG are analyzed.The influences of important parameters,like tilted angles,index modulation amplitudes,length of gratings on the characteristics of TFBG are studied by simulation.They are analyzed theoretically,which provides guidances for fabrication.(3)The fabrication system platform based on UV laser and phase mask,and the processing,technological process of fabrication and post processing are introduced.Two tilting techniques are introduced in detail,the expression of grating plane tilted angle and tilting angle are inferred,and their advantages and disadvantages are discussed.Measurement system is described,and the key points for attention during measuring TFBG,CFBG and CTFBG are introduced.Combined with their characteristics,the measured results of TFBG,CFBG and CTFBG are analyzed.(4)The stimulated Raman scattering(SRS)in high power laser system is introduced.Then,some approaches to suppress the SRS are listed and compared,and employing the CTFBG as a SRS filter is proposed.A system to test the effect of filtering is established and correlative experiment is carried out.Experimental results demonstrate that one CTFBG can suppress the SRS about 20 dB effectively.