unit of dispersion is:

(picosecond)/ nanometer kilometer

Dispersion affects optical fibers in the sense that dispersion causes a disruption in the frequency of lights waves and can focus the wavelength nature of light.

Cl2 is non polar.So there are london dispersion

Yes,CH4 is non polar.So it has london dispersion.

In the fiber optics there are different types of losses; these are the bending loss, absorption loss, dispersion loss, and scattering losses. Bending losses is the loss which exists when an optical fiber undergoes bending, this includes macroscopic and microscopic bending. Absorption loss is the absorption of light energy resulting in dimming of light at the end of the fiber, this includes intrinsic and extrinsic absorption. Dispersion loss is the distortion of the signal as it travels along the fiber optic cable, this includes intermodal and intramodal dispersion. Scattering losses occurs due to microscopic variations in the material density, compositional fluctuations, structural homogeneities and manufacturing defects, this includes linear and non-linear scattering.