Submicrometer displacement sensing based on multimode fiber speckle field

Abstract

It is well known that by perturbing a multimode fiber, a complicated speckle pattern can be observed in the far field. The speckle field is highly sensitive to the fiber status changes, and this sensitivity is caused by the surrounding sensing environment. The proposed technique is based on the fact that taking the intensity inner product of two speckle fields, for example, before and after the perturbation, represents the similarity between the two speckle patterns that is related to the external changes (such as strain or displacement). Preliminary analysis and experimental demonstrations are provided, in which we have shown that the sensitivity of the proposed multimode fiber sensor can be as high as 0.1 μm.