Spectral Characteristics of Cascaded Uniform FBGs of Varying Lengths

In this paper, the spectral characteristics of cascaded uniform FBGs of varying lengths are analyzed and simulated using MATLAB. Spectral characteristics of FBGs are usually expressed in terms of reflectivity, bandwidth, or Full Width at Half Maximum (FWHM) and the side lobes. The maximum reflectivity and narrow bandwidth are usually essential for optical communication applications where FBGs are used as narrowband filters. Often, as the number of cascaded FBGs increases, reflectivity decreases. In order to improve the reflectivity, a cascaded FBGs structure has been proposed. The proposed cascaded FBGs structure maintains almost constant reflectivity even for more number of stages. A narrow bandwidth can also be enhanced with the help of the proposed structure. The simulated results show that the reflectivity is improved to 98.3% and bandwidth of 0.177 nm with minimization of side lobes can be achieved with the help of the proposed cascaded FBGs structure.