Auto-testing method of angle of optical fiber endface based on principle of geometric projection and mathematical morphology

摘要

Optical fiber connection with bevelled endface is applied to enhance return loss in optical fiber communication, so the angle of endface is an important parameter of the optical fiber that needs to be tested before connection. Perfect optical fiber endface is an area in an intersection plane across a cylinder of the optical fiber and the projection of the area is an ellipse or line relative to the bevelled angle. Because imaging of microscope objective follows the principle of geometric projection, when the optical fiber endface is imaged in CCD by a microscope objective, the image is the amplified projection of the optical fiber endface. With a video capture card, the digital image is formed in the computer. The equation of the projection is resolved by means of digital image processing, and then the angle degree is calculated. In course of image processing, edge detection and thinning of the image is based on mathematical morphology and curve fitting is based on least square method. It is shown by the result that the precision of the angle degree is between 0.2°in the method.