Electromagnetic shielding characteristics of optical-fiber feedthroughs

A number of commercially available optical-fiber connector styles ST, SC, and FC were tested to determine the extent to which their use in bulkhead adapter feedthroughs would compromise the shielding of electromagnetic interference for electronic enclosures. Connectors and adapter barrels made from metal, ceramic, and polymer materials were included in the tests. The tests were carried out using a nested reverberation cell and covered a frequency range from 1 to 16 GHz. Although we rely on data acquired by making shielding effectiveness (SE) measurements, we report the results in terms of a transmission cross-section which is the ratio of the power coupled into an enclosure through an aperture to the power per unit area incident on the aperture. The amount of coupling through the feedthroughs we tested varied over 70 dB. The shielding of an all-metal FC connector system was nearly equal to that of a blank reference plate. In some cases, a feedthrough coupled more energy into the enclosure than was coupled through the empty hole required to mount the adapter barrel. Unlike SE, the transmission cross sections do not depend on the volume, shape, or construction materials of the enclosure and can be used to estimate the degradation in the SE for enclosures other than our reference cell. The uncertainties in the reported transmission cross sections are calculated to be /spl plusmn/3 dB and are small compared to the differences between the measured cross sections.