Analysis of leaky modes and Bragg fibers using transmission line equivalent T-circuits

In this letter, we have extended the transmission line (TL) technique to calculate the effective index of leaky modes and demonstrated it by using the model of Bragg fibers. From Maxwell´s equations we derived a TL equivalent circuit for the Bragg fiber and we demonstrate how it can be used to determine the mode effective index. Transverse magnetic modes of Bragg fibers and mode bandgap structures can be analyzed using the TL method. Furthermore, we demonstrate that this model allows us to carry out the inverse problem and synthesize the exact refractive index profile if the desired Bragg fiber near field is available. The accuracy of the reconstructed waveguides is also examined numerically.