Different propagation modes have different propagation velocities and phases, resulting in time delay and widening of optical pulses after long-distance transmission. This phenomenon is called modal dispersion of the fiber. It gives better signal quality and less mistakes. Multi-mode fiber has a fairly large core diameter that enables multiple light modes to be. Figure below shows a simple topology used to measure the DMD of a multimode fiber: Since DMD is a measure of the fiber's spatio-temporal impulse response, it is important to use an input pulse that approximates a delta function in both space and time. The DMD measurement is performed by scanning. Temporal delays or latency in optical fiber refer to the time it takes for a light signal to travel a certain distance from the source to the receiver.
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