Changes in speckle patterns in an output light spot from an optical fiber to be caused by load application of small weight level

Abstract

For the purpose of utilizing changes in speckle patterns to be observed in an output light spot from an optical fiber for sensing applications, certain load was applied onto an optical fiber in which laser beams from a laser diode were propagating, and resultant changes in the output light intensity were measured. In order to realize effective load application onto the optical fiber, load application mechanism was employed in which several ridges were intentionally provided onto opposite flat plates. A jacket-covered communication-grade multi-mode glass optical fiber was placed in the load application mechanism so that corrugated bending of the fiber was intentionally induced via load application due to the ridges. Laser beams propagated through the optical fiber was allowed to be output and projected onto a PV cell panel disposed at about 10 cm from the fiber end. The output voltage from the PV cell panel was measured as the output light intensity from the optical fiber. For the load application up to 40 kg, certain changes (reductions and increases) in the output light intensity were measured with increasing or decreasing level of load application with sufficient reproducibility. Even with load application of smaller load level, similar changes were observed. Such changes (reductions and increases) in the output light level with increasing and decreasing load application levels were caused by changes in speckle patterns contained in an output light spot from the optical fiber.