What is modal bandwidth, and how does it affect what distances gigabit Ethernet can travel over fiber?

Modal bandwidth is often referred to in telecommunication as the maximum signaling rate for the specified distance or the maximum distance for a particular signaling rate. It is expressed in MHz.km and signaling rate is mentioned in MHz. This is peculiar for multimode fibers as to the exact amount of data transmitted through a fiber at a given wavelength. Modal bandwidth depends on DMD or differential mode delay.
Fiber optic cables use light as a signal. This light or mode does affect the distance Gigabit Ethernet can travel over fiber. Light signals take different modes due to which light disperses. Here, the length of the fiber is a significant factor. If the fiber length is long, the modal bandwidth effect is more. So, these two are directly proportional to each other.