A variational method to approximate the field of weakly guiding optical fibers by Laguerre-Gauss/Bessel expansion

In the analysis of weakly guiding single-mode optical fibers, Gaussian and modified-Gaussian approximations appear inadequate to obtain accurate resul ts at low normalized frequency for general refractive index profiles. To ov ercome such limitations we propose an expansion in terms of Laguerre-Gauss functions to represent the field in the fiber core. A modified Bessel funct ion is instead used to describe the field in the cladding. All parameters d efining the approximate field are evaluated by a variational method. We sho w that the proposed approximation is very accurate in the low normalized fr equency limit too and can be particularly valuable to analyze dispersion-sh ifted fibers with triangular refractive index profile.