Cross-Entropy Optimization for the Design of Triangular FBG Filter With Asymmetrical Spectrum

This letter reports the use of optimization methods to design triangular fiber Bragg grating (TFBG) filter with asymmetrical spectrum. In the optimization methods, TFBG synthesis problems are formulated as nonlinear objective functions, and stochastic optimization techniques are applied to search for index modulation profiles that minimize the difference between the synthesized and targeted spectra. However, the performances of traditional stochastic optimization techniques are affected by the initial guess. A poor initial guess may result in low-efficiency optimizations and easily get trapped into local solutions; in some cases, it may even lead to a false result. Accordingly, we introduce the use of cross-entropy optimization (CEO) in searching for the optimal index modulation profiles. CEO is an effective algorithm that solves various continuous multiextremal optimization problems and demonstrates robustness with respect to starting conditions. Computer simulation results show that the index modulation profiles obtained using the proposed method performed better compared with those obtained using the conventional covariance matrix adaptation evolution strategy (CMAES). In addition, CEO also provides a reliable convergence to the near-optimum solution. These findings indicate the CEO is more suitable than CMAES for the design of TFBG filters with asymmetrical spectrum for sensor applications.