Zero dispersion in attenuation optimized doubly clad fibers

Abstract
In a weakly guiding single-mode fiber, there exists an optimum value for the HE11mode spot size, which minimizes splicing and microbending losses. Zero dispersion and this optimum spot size for the mode can simultaneously be achieved with any inner-cladding depth; increasing the inner-cladding depth, however, allows smaller dopant concentrations in the core and thus lower intrinsic losses, but this induces an enhanced sensitivity to curvatures and to parameter fluctuations. When the inner-cladding depth is sufficiently high, on the other hand, the fundamental mode has a nonzero cutoff and dispersion can be minimized over a wide spectral range. At\lambda = 1.55\mum, we determine the optimum value for the inner-cladding depth from criteria of both sensitivity to bending and fabrication tolerances or by requiring a given mode dispersion behavior over a wide spectral range.