differential mode delay (fiber optics) (DMD)
Differential mode delays( DMD) are signal distortions due to different propagation times ofmodes in optical fibers. They are also referred to as multimode group delays because lower and higher order modes propagate differently in multimode fibers and thus have different propagation times.
Differential mode delays can also be caused by partial excitation of laser light injected into a multimode fiber.
When light signals are transmitted in optical fibers, they are deformed by profile dispersion, which is due to production tolerances in the manufacture of optical fibers. The transmitted light pulses are thus broadened and flattened, leading to the corresponding DMD delays.
InGigabit Ethernet and in even faster Ethernet variants, the DMD distortions can affect the transmission specifications. They are therefore specified.