Multi-mode optical fiber

Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be propagated and limits the maximum length of a transmission link because of modal dispersion.

The LED light sources sometimes used with multi-mode fiber produce a range of wavelengths and these each propagate at different speeds.

In contrast, the lasers used to drive single-mode fibers produce coherent light of a single wavelength.

Single-mode fibers are often used in high-precision scientific research because restricting the light to only one propagation mode allows it to be focused to an intense, diffraction-limited spot.

Fibers that meet this designation provide sufficient bandwidth to support 10 Gigabit Ethernet up to 300 meters.

This requires the SFP+ interface to support electronic dispersion compensation (EDC) however, so not all switches, routers and other equipment can use these SFP+ modules.

LEDs have a maximum modulation rate of 622 Mbit/s [citation needed] because they cannot be turned on/off fast enough to support higher bandwidth applications.

Some 200 and 400 Gigabit Ethernet speeds (e.g. 400GBASE-SR4.2) use wavelength-division multiplexing (WDM) even for multi-mode fiber[10] which is outside the specification for OM4 and lower.

The net effect causes the light pulse to spread over distance, introducing intersymbol interference.

To combat modal dispersion, LOMMF is manufactured in a way that eliminates variations in the fiber which could affect the speed that a light pulse can travel.

Duplex LC (330 m QSFP+ eSR4[19]) Duplex LC (550 m QSFP+ eSR4[19]) The IEC 61280-4-1 (now TIA-526-14-B) standard defines encircled flux which specifies test light injection sizes (for various fiber diameters) to make sure the fiber core is not over-filled or under-filled to allow more reproducible (and less variable) link-loss measurements.