Design of chirped fiber Bragg grating with ideal box spectra and smoothly time delay

A chirped fiber Bragg grating with ideal box spectra and smoothly time delay is designed. The outer cladding of the fiber is etched as sinusoidal function. When the tension applied to the grating in fabricated process is threw off, the fiber grating not only exhibits a flattop spectrum with steep edges and high reflectivity, but also has a smoothly time delay curve. The bandwidth utilization defined as the ratio of -1:-30 could be achieved a larger value(>0.91).