Abstract

We have constructed and evaluated a video microscope for performing dimensional measurements on optical fibers—what the industry calls the gray-scale method. We think that our results may be of interest to video microscopy, machine vision, and critical dimensional measurements.¹ Our microscope consists of a common 40×, 0.65 N.A. microscope objective, a 550 nm interference filter, an illumination system, and a chargecoupled-device video camera, all mounted on a miniature optical bench. The field of view is 150 × 150 µm, so the image can encompass the entire end face of an optical fiber. Using a calibrated reticle, we have calibrated the distance scale of the microscope with an accuracy of ~±50 nm over the 150µm field of view. Using a calibrated linewidth standard, however, we have found a systematic error of 0.1-0.2µm on measurements of lines whose width is many times the resolution limit of the system. Because this systematic error depends on the illumination of the sample, we think it will be necessary to develop a calibrated fiber before the systematic error can be reduced below ~0.1 µm.

© 1990 Optical Society of America