For the HE11 mode, group index is equal to core group index at a specific V-number which is a function of the core-clad index difference.  Snyder & Love "Optical Waveguide Theory" (1983) includes approximations valid in the weakly guided limit in their table 14-3, page 313.  If you know Δ, solve for V.  Then calculate distortion parameter using their formula in the same table, and hence find waveguide component of group velocity dispersion using equation 11-58 on page 229.   Table 14-4 or figure 14-3 may be more convenient if you don't need exact values.

More generally, if you know core and clad materials, core diameter and core-clad index difference, solve the wave equation at your operating wavelength.  Calculate group velocity and dispersion - either by differentiating the propagation constant with respect to optical frequency, or by applying the mode field integrals presented by Snyder & Love in table 11-1 or 13-2.

The group index and dispersion of core and cladding materials can be calculated by interpolating between the compositions measured by Fleming "Material dispersion in waveguide glasses", IEE Electronics Letters, vol 14, no 11, pp 326-328 (1978).  Use Fleming's Sellmeier coefficients to calculate refractive index, group index and dispersion at any wavelength.

http://ieeexplore.ieee.org/document/4241112/

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4241112

Thank you, I will work it out

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