The main difference between multi-mode and single-mode optical fiber is that the former has much larger core diameter, typically 50.100 micrometers; much larger than the wavelength of the light carried in it. Because of the large core and also the possibility of large numerical aperture, multi-mode fiber has higher "light-gathering" capacity than single-mode fiber. In practical terms, the larger core size simplifies connections and also allows the use of lower-cost electronics such as light-emitting diodes (LEDs) and vertical-cavity surface-emitting lasers (VCSELs) which operate at the 850 nm and 1300 nm wavelength (single-mode fibers used in telecommunications operate at 1310 or 1550 nm and require more expensive laser sources. Single mode fibers exist for nearly all visible wavelengths of light).
However, compared to single-mode fibers, the multi-mode
fiber bandwidth-distance product limit is lower. Because multi-mode fiber has a larger core-size than single-mode fiber, it supports more than one
propagation mode; hence it is limited by modal dispersion,
while single mode is not.
The LED light sources sometimes used with multi-mode fiber
produce a range of wavelengths and these each propagate at different speeds.
This chromatic dispersion is another limit to the useful length for
multi-mode fiber optic cable. In contrast, the lasers
used to drive single-mode fibers produce coherent light of a single
wavelength. Due to the modal dispersion, multi-mode fiber has higher
pulse spreading rates than single mode fiber, limiting multi-mode fiber's information transmission capacity.