A numerical study of pulse switching in nonlinear nonuniform fiber Bragg gratings

We have analyzed pulse switching in nonlinear uniform and Gaussian apodized FBGs. For the uniform grating, the sidelobes of the wavelength response cause the pulse breakup due to their spectral components. The nonlinear effect causes an equivalent wavelength reduction. This reduction can be used to switch pulses if the initial wavelength operating point is near a transition from 0 to 1 (or 1 to 0) in the reflectivity curve. However, the rise of the nonlinearities causes a temporal pulse breakup that indirectly reduces the peak power of the pulses. For this reason, the initial operating point should be as close as possible to the transition and that transition should be as abrupt as possible. The use of raised-cosine apodized gratings may improve the nonlinear switching characteristics. The pulse breakup caused by the nonlinearities can be reduced by the use of soliton-like pulses, i.e., sech(t). It has been shown the equations at high input peak powers reduce to the well-known nonlinear Schrodinger equation for λ/λ_D