In this paper,we introduce a new model, of long-period fiber grating, by taking the value of ambient refractive index greater than the refractive cladding index, where the difference between them must equal(≈0.2).The results show the change in power attenuation coefficient, where it increases with the increase in refractive ambient index. The power attenuation coefficient shift shows a dramatic change of a sharp increase from 0.00dB to ≈ 0.03788dB and 0.00dB to ≈ 0.04675dB and 0.00dB to ≈ 0.06875 dB. Here this model is used as sensor for shifting in input signal (15nm, 5nm).

Key Word: Long Period Fiber Grating, single mode fiber optical