The Bowtie effect in cylindrical waveguides

Modes in step-index fibers are often studied using a scalar model, born to the approximations allowed by the assumption of low refractive index contrast. Such approximations lead to a perfectly linear polarization in the resulting modes, among which the Bessel-like ones are attracting increasing interest for their many applications. These modes, as described by the scalar model, have a circularly symmetric irradiance. Nevertheless, in some cases, their symmetry disappears as their intensity profile exhibits angular ripples that cannot be foreseen by the scalar approach. In this paper, this effect is thoroughly analyzed.