<title>Measurement of cross talk in order-packed image fiber bundles</title>

Abstract

This paper describes a novel technique to quantitatively measure cross talk in order-packed image fiber bundles using a calibrated optical video system. At the input end of the fiber bundle, by carefully matching numerical aperture of the focusing lens, light is coupled into one single fiber. At the output end, a large area around the excited fiber is monitored using a video CCD array. The light intensity in integrated and the ratio between output light in adjacent fibers and output light from the excited fiber constitutes the percentage cross talk. Additionally, static modulation transfer function (MTF) measurements together with visual inspection was used to correlate the cross talk to the imaging properties of an optical fiber bundle. Comparison between different samples results in the following observations: typical cross talk varies between 1-15% for good versus bad imaging fiber bundles; image fiber bundles with less cross talk show higher static MTF at low spatial frequencies; different defects in the fiber bundle manifest themselves by specific signatures, both in the static MTF and the cross talk; when the cross talk is less 5%, the spatial cut-off frequency is not altered; cross talk decreases when reducing the numerical aperture of the coupling system.