What primarily leads to the increase in dispersion within fiber optic cables?

The increase in dispersion within fiber optic cables is mainly attributed to increased cable length. As light travels through the fiber, it can spread out or disperse due to various phenomena, and this dispersion effect intensifies over greater distances. Specifically, modal dispersion and chromatic dispersion are two types of dispersion that occur predominantly due to the fiber’s physical characteristics and the light's interaction with the material over longer paths.

Increased cable length allows for more opportunities for light to reflect off the core and travel different paths, which results in a greater spread of the signal. This is why longer fibers often require more precise technology and quality materials to manage the effects of dispersion effectively, ensuring signal integrity over considerable distances.