Spectra of dual overwritten fiber Bragg grating

The perturbation to the refractive index induced by dual overwritten fiber Bragg grating (FBG) is analyzed, and the coupled-mode equations are obtained. The spectral characteristics that can be achieved in dual overwritten fiber gratings are investigated by numerical simulation. It is found that the spectral characteristics are affected significantly by period difference Delta Lambda, primary phase difference Delta phi and grating length L. Moreover, multiwavelength reflection and strong second harmonics will occur in dual written FBG when the nonlinear W-induced index perturbation exists, which is very useful for multichannel wavelength-division multiplexing. The results concluded in this paper are conducive to the fabrication and applications of dual overwritten FBGs. (C) 2001 Elsevier Science B.V. All rights reserved.