The transmission near-field scanning technique can be used for determining the refractive index profile, the maximum core-cladding refractive index difference and/or numerical aperture, the geometrical characteristics and the mode-field dimensions in single-mode waveguides. In the experimental apparatus presented in the paper, the near-field pattern under test is magnified onto the faceplate of a vidicon camera, the video signal is sent to a computer--controlled video digitizer with single frame buffer memory organized as 512x512x8 bits. The incoming signal is digitized in real time to 8 bit resolution. Algorithms developed to opti-mize the scanning routine and to derive waveguide parameters from the measured data are described. As measured signals are usually noisy, techniques which reduce the noice level are also presented. Futhermore, techniques applied to compensate the vidicon sensitivity nonuniformity and nonlinearity are reported. Some examples of the results of measurements of the refractive index profiles and geometrical parameters like: core and cladding diameters, core and cladding non-circularities and core/cladding concentricity errors are presented.

Date Published: 9 February 1989
PDF: 8 pages
Proc. SPIE 1028, Scanning Imaging, (9 February 1989); doi: 10.1117/12.950353

Published in SPIE Proceedings Vol. 1028:
Scanning Imaging
Tony Wilson, Editor(s)