Design of graded refractive index profile for silica optical fibers with core diameter 42 mm and reduced differential mode delay

We present method for design of refractive index profile for silica GeO2-doped graded-index few-mode optical fibers with reduced differential mode delay and suppressed mode nonlinearity due to enhanced core diameter up to 42 mm. Proposed solution is based on combination of well-known overlap integral method and earlier on developed modified Gaussian approximation generalized for analysis of silica weakly guiding optical fibers with single solid outer cladding and arbitrary axially-symmetric refractive index profile. This approach provides ability to derive analytical expressions for guided mode delays. Therefore, the objective function is represented as a sum of squares of deviations between mode staff delays and reference value corresponding to refractive index profile of current iteration. Based on developed method we performed computation for various combination of the reference mode delay and first iteration profile parameter. Some results of desired graded-index profile for a few-mode optical fibers 42/125 providing differential mode delay less then 50 ps/km over central region of "C"-range are represented.