Modified coupled-mode model for thermally chirped polymer Bragg gratings.

A modified coupled-mode (CM) model is proposed for the optical behavior of thermally chirped Bragg gratings. The model accounts for the axial gradient in the modulation wavenumber, which has been ignored in the classical CM model. The model is used to characterize the optical behavior of a polymethyl methacrylate-based polymer Bragg grating subjected to nonisothermal conditions.