Zero dispersion in attenuation optimized doubly clad fibers

In a weakly guiding single-mode fiber, there exists an optimum value for the HE
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mode 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\mu
m, 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.