Dispersion in Optical Fibers
... this equation implies that at the point of zero dispersion, λD , where β̈ = 0
the group velocity, vg as a function of ω has a minimum (the derivative is
zero). For wavelengths λ < λD , β̈ > 0 and the fiber is said to exhibit normal
dispersion. In this regime (dvg /dω) < 0, which means high-frequency ...