Fiber Optic attenuators

In practical terms, the larger core size simplifies connections & also allows the use of lower-cost electronics such as light-emitting diodes (LEDs) & vertical-cavity surface-emitting lasers (VCSELs) which operate at the 850 nm & 1300 nm wavelength (single-mode fibers used in telecommunications operate at 1310 or 1550 nm & need more pricey laser sources. Single mode fibers exist for 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 bigger core-size than single-mode fiber, it supports over 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 & these each propagate at different speeds. In contrast, the lasers used to drive single-mode fibers produce coherent light of a single wavelength.



This chromatic dispersion is another limit to the useful length for multi-mode fiber optic cable. Because of their larger core size, multi-mode fibers have a higher numerical aperture which means they are better at collecting light than single-mode fibers. Due to the modal dispersion in the fiber, multi-mode fiber has higher pulse spreading rates than single mode fiber, limiting multi-mode fibers information transmission capacity.