What is waveguide dispersion in optical fibres?

Waveguide dispersion (Δτ_w):

Waveguide dispersion occurs because of the dependence onto the velocity of propagation of every wavelength onto the geometry of the fiber. This is commonly negative. It is the pulse compresses.

Usually, total dispersion Δτ= Δτ_im+ Δτ_mat + Δτ_w

In single mode fibers, the contribution is mainly only through material and waveguide dispersion. The figure demonstrated below provides the dispersion characteristics for a characteristic standard single mode fiber. This can be seen which the material dispersion and waveguide dispersion are equivalent in magnitude and cancel all other off at the wavelength of 1310nm. Therefore this wavelength termed as the zero dispersion wavelengths was the preferred operating wavelength for second generation fiber optic communication systems.