Improving the performance of fiber gratings with cladding being etched as hyperbolic function

A new grating structure of cladding being etched as hyperbolic function along the grating length is introduced to improve their performance. The fiber grating exhibits a flattop spectrum with steep edges and high reflectivity when tension is applied to it. The bandwidth utilization defined as the ratio of −1:−30 could be achieved a larger value (>0.9689). The −3 dB bandwidth and the bandwidth utilization could be tunable with the increment of tension applied to the grating and the etch factor.