Rotation phenomena of speckle patterns observed in an output light spot from an optical fiber

摘要

When coherent light beams (laser beams) are incident on one end of an optical fiber, transmitted to another end to exit from there so as to form an output light spot on a screen, non-uniform intensity distribution called speckle patterns is often recognized in the output light spot. The authors have confirmed that when a multimode optical bare fiber is placed in a loop onto a support plate, the speckle patterns in the output light spot appear to rotate while rotating the support plate. In this paper, even when an optical fiber was placed in a U-shape, instead of a loop, onto the support plate, the similar rotation of speckle pattern was observed. Furthermore, it was confirmed that a distance between the optical fiber placed in parallel at the edge of the support plate provides certain influences on the observed rotating characteristics of the speckle patterns. Thus, the pattern rotation seems to be caused by upward and downward displacements of the optical fiber at the edge of the support plate. In addition, even in the case where a jacket-covered and connector-attached optical fiber was placed in the U-shape on the support plate and a laser diode was employed as a light source, similar speckle pattern rotation was recognized.