Out-of-plane displacement measurement for an optical fiber image transmission element using optical flow

To realize the industrial in-situ deformation detection of an optical fiber image transmission element, a method for out-of-plane displacement detection based on the combination of optical flow and an image spherizing algorithm is presented. After capturing the 2D deformation images, the out-of-plane displacement can be extracted from the in-plane displacement estimated by the optical flow method, which means that the out-of-plane displacement information contained in a 2D image is fully used. The principle of the Brox optical flow method is introduced and the accuracy of the method is proven by comparing test results with the digital image correlation method. Experimental results show that the relative errors and the absolute errors of the measurement are less than 2% and 0.1 µm. Because the optical flow algorithm introduces a time parameter and the smoothness assumption, the new method is more appropriate for dynamic and microscale out-of-plane displacement measurement. Unlike conventional methods, it does not need phase unwrapping or frequency domain conversion during detection and has many attractive characteristics such as nondestructive testing, a simple arrangement, and low errors. This method has been applied to the industrial in-situ monitoring of an optical fiber image transmission element.