Hello Ajay Vyas
Nonlinear coefficient really depends upon n2(non-linear coefficient),Aeff of optical fiber.In the paper you have attached value of gamma is 2.09/w/Km for SMF and 6.04 in the case of DCF.Units of n2 is m2/W and for Aeff in um2.you can calculate gamma by using formula
Gamma=2*pi*n2/Wavelength*Aeff
Default value of n2 in SMF28 is 26e-21 and Aeff is 70um^2.Rest it vary according to application or alter by the manufacturer
Discussion already has done on this topic.Please check the link given below
Regards