Correlated modification of the speckle pattern in an interferometer made of a multimode fiber-optic waveguide

An investigation was made of correlated modification of the speckle pattern in the field of radiation leaving a single-fiber multimode interferometer when the waveguide was subjected to an external perturbation. A correlation between the changes in the speckle pattern was observed in the near- and far-field zones of the radiation emerging from the waveguide. A relationship was obtained for determination of the maximum size of the speckle correlation region. The method of spatial filtering was proposed for isolating the effects of a correlated modification of the speckle pattern. The use of a spatial filter made it possible to increase the efficiency of fiber-optic sensors.