Hybrid Tabu Algorithm for the Synthesis and Fabrication of Fiber Bragg Gratings

Abstract

Fiber Bragg gratings (FBGs) are widely employed as optical filters for performing various functions such as add/drop multiplexers, dispersion compensators and multiplexers/demultiplexers for use in optical communication systems and optical sensors because of a number of advantages that include low insertion loss, low polarization sensitivity, all-fiber geometry, compactness, easy fabrication and low cost (Kashyap, 1999; Othonos & Kalli, 1999). In addition, the technology of ultraviolet (UV) photoinduced FBGs is quite mature to allow the fabrication of a wide variety of FBGs with complex characteristics. To meet the increasing demand for large capacity of the next generation of optical communication systems (i.e., wavelength division multiplexing (WDM) networks) and optical sensors, there is an important need for a powerful design tool that can be used for the synthesis or design of FBGs from the specified frequency responses that can be practically realized. This synthesis or inverse problem of determining a FBG structure from a given frequency response (i.e., magnitude and phase responses) is common in many application areas. The design tool must be efficient and reliable to enable the synthesis of FBG-based filters with prescribed frequency responses, depending on the application requirements. That is, the design tool must be able to determine the index modulation profile and hence the structure of an FBG from a given frequency response. In addition, the design tool must be powerful enough for use in the diagnosis or characterization during and after fabrication of an FBG. Although several synthesis methods such as those based on the layer-peeling algorithm have been proposed for the synthesis of FBGs from the specified frequency responses, the index modulation profiles of the synthesized FBGs are not optimized and are often complex, making practical realization difficult (Feced et al., 1999; Poladian, 2000; Skaar et al., 2001; Rosenthal & Horowitz, 2003). To overcome this problem, optimization methods have been demonstrated as an attractive approach because it allows weighting mechanisms to be incorporated into the desired frequency response of an FBGbased filter to be synthesized, resulting in an optimum and practically realizable index modulation profile of the FBG structure. Furthermore, the optimization algorithms also allow additional constraints to be included in the weighting mechanisms of the specified frequency response to suit certain condition(s) or constraint(s) of a particular fabrication system. In optimization, the FBG synthesis problems are formulated as nonlinear objective