Fabrication of high quality chirped fiber Bragg grating by establishing strain gradient

To fabricate chirped fiber Bragg grating (CFBG) with high reflectivity and accurately controlled chirp profile with low cost, we develop the CFBG fabrication technique based on strain gradient: fabricating CFBG using fabricated fiber Bragg grating (FBG) by establishing strain gradient along the length of grating. We theoretically analyze the form of such CFBGs, and study the characteristics of gratings using piecewise-uniform approach. It is shown that increasing UV-induced index change or the length of the grating or both are the efficient ways to obtain high quality CFBG with high reflectivity and good reflection spectrum. The dispersion of this grating is decided by and varies inversely with the slope of the strain gradient along the length of the grating, not decided by UV-induced index change or by the length of grating. One can control the dispersion and the chirp profile by adjusting the slope of the strain gradient. Based on the theoretical analysis, we have fabricated CFBG whose reflectivity is maintained at 100% in a large range of strain gradients.