The Effect of Refractive Index Modification Position and Duty Cycle on Performance of LPFGs

Long period fiber gratings (LPFGs) are fabricated in standard single mode fibers with femtosecond laser. The position of optical fiber refractive index modification is controlled exactly. It finds that the depth of resonant rejection bands rely on the position of optical fiber refractive index modification. Optical fiber refractive index modification is in proper scope, the resonant rejection bands are strong. Changing the duty cycle of LPFGs, the background losses and the harmonic resonance peaks can be sustained. However, when the duty cycle is reduced to a certain extent, although there is a periodic perturbation of the properties of the optical fiber, the attenuation of LPFG is very weak.