Speckle pattern

Speckle pattern: In optical systems, a field-intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations.

Note: In a multimode fiber, a speckle pattern results from a superposition of mode field patterns. If the relative modal group velocities change with time, the speckle pattern will also change with time. If differential mode attenuation[?] occurs, modal noise[?] results.

Source: from Federal Standard 1037C and from MIL-STD-188