Attenuation-optimized dispersion-flattened quadruple-clad fibers with moderate < e1 > F < /e1 > -doping in the first inner cladding

The arbitrary quadruple-step-index structure is examined as a new design model for dispersion-flattened fibers to obtain more degrees of freedom and simulate the practical fiber profile. The effects and limitations of structural factors are examined. Under the severe condition of the first clad depression -Delta < e1 > n < /e1 > (1) < 0.004, the refractive index profile is optimized for both dispersion compensation and low loss. A number of fibers were fabricated by modified chemical vapor deposition (MCVD) process with a typical loss of 0.23 dB/km at 1.55 mum and low dispersion over the 1.3-mum and 1.55-mum windows