Numerical optimization and simulation to wavelength-division multiplexing isolation filter consisted of two identical long period fiber grating

We gave an analysis about the wavelength-division multiplexing isolation filter consisted of two concatenated long period fiber grating (LPFG), and the numerical simulation was performed by transfer matrix method. The key factors in design this high performance filter was proposed. Based on the key factors, flat transmission spectrum of the LPFG in range of 80 nm was obtained by the particle swarm optimization algorithm. The simulation results demonstrate that such type of isolation filters have equal frequency spacing, high isolation, and neglectable dispersion in the pass band, and the channel spacing can be tuned by tuning the fiber length between the two concatenated LPGs.