Analysis of rotation phenomena of speckle patterns in an output light spot from multimode optical fiber with deep learning scheme

When laser light beams are allowed to propagate from one end of a muti-mode optical fiber to the other end and further to be output onto a screen, irregular patterns called as speckle patterns can be observed in an output light spot. The authors previously reported the rotating phenomenon of such speckle patterns when the optical fiber was placed onto a support plate in a loop-shape and the support plate was tilted. In this paper, the method for estimating tilted angles of the support plate was tried through classification of speckle pattern images by ResNet-18 trained using transfer learning. As a result, the model with a classification accuracy of approximately 99.9% in the measurement range of -10 to +10 degrees of tilted angles was realized.