Design of optimal length low-dispersion FBG filter using covariance matrix adapted evolution
ABSTRACT The design of a low-dispersion fiber Bragg grating (FBG) with an optimal grating length using covariance matrix adapted evolution strategy (CMAES) is presented. A novel objective function formulation is proposed for the optimal grating length low-dispersion FBG design. The CMAES algorithm employs adaptive learning procedure to identify correlations among the design parameters. The design of a low-dispersion FBG filter with 25-GHz (or 0.2 nm in the 1550-nm band) bandwidth is considered. Simulation results, obtained using the codes available in public domain (the codes are available from the third author), show that the CMAES algorithm is more appropriate for the practical design of length optimized FBG-based filters when compared with the other optimization methods.
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ABSTRACT: A hybrid Tabu algorithm has been presented for the synthesis and fabrication of FBG-based filters with specified frequency responses. The hybrid Tabu algorithm is a two-tier search that employs the global staged continuous Tabu search (SCTS) algorithm and a local optimization algorithm (i.e., the Quasi-Newton method). The first step of the hybrid Tabu algorithm (which employs the global SCTS algorithm) produces a "promising" grating structure which is then further optimized by the second stage of the hybrid Tabu algorithm (which employs the Quasi-Newton algorithm) to yield the final optimized solution or grating structure. In the hybrid Tabu algorithm, the synthesis problem of an FBG is formulated as an objective function which measures the error between the optimized reflection frequency response of an FBG based on the hybrid Tabu algorithm and the target frequency response, and the optimized solution or grating structure has the smallest error. The FBG-based filters are based on non-uniform FBGs with a wide variety of frequency responses. The transfer matrix method (TMM) has been employed to model a non-uniform FBG because it allows the magnitude and phase responses of a non-uniform FBG to be obtained with reasonably high accuracy. In TMM, a non-uniform FBG can be modeled using either the cascade of serially-connected uniform sub-gratings (this model is sufficient for obtaining the magnitude response when the phase response is not important) or the cascade of serially-connected apodized sub-gratings (this model must be used when both the magnitude and phase responses are important). The effectiveness of the hybrid Tabu algorithm has been demonstrated through the design and fabrication of 25-GHz-bandwidth FBG-based bandpass filters with near-squared bandpass responses and the design of 50GHz-bandwidth FBG-based linear phase filters with near-squared bandpass responses and flat group delay responses, which have potential application in optical communication systems operating in the 1550 nm wavelength window. For future work, the presented hybrid Tabu algorithm can be further developed into a powerful toolbox that can be efficiently and reliably used for the synthesis and fabrication of a wide variety of FBG-based filters with specified complex frequency responses to meet the increasing demand of sophisticated signal processing and filtering functions of the next generation of optical sensors and optical communication systems. Furthermore, the powerful design toolbox must be powerful enough for use in the diagnosis or characterization during and after fabrication of an FBG.Tabu Search, 09/2008; , ISBN: 978-3-902613-34-9
- Journal of Microwaves, Optoelectronics and Electromagnetic Applications. 06/2011; 10(1):165-178.