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Design of fiber Bragg gratings using the simulated annealing technique for an ideal WDM filter bank

We propose new methodology for designing an ideal bandpass filter as a cascade of two piecewise uniform fiber Bragg gratings (followed by a 100% fiber-optic reflector). With the expense of a more complicated structure, we are able to obtain an almost ideal bandpass filter with a constant group delay. The first piecewise-uniform fiber Bragg gratings are designed to get the desired (i.e., rectangular) bandpass amplitude spectrum. The second piecewise-uniform fiber Bragg gratings (together with the reflector) are designed to flatten the group delay characteristics of the first fiber Bragg gratings. The parameters of fiber Bragg gratings are determined by using the simulated annealing technique followed by the steepest descent algorithm.