Low-temperature transmission loss in loose tube fiber optic cables

Abstract

Large optical losses in singlemode fibers have been reported in loose tube fiber optic cables exposed to extremely low temperatures (-20 degree(s)C to -40 degree(s)C). These losses have occurred predominantly at 1550 nm (although some transmission systems at 1310 nm have also been affected) in aerial cables and were confined to the cable section adjacent to a splice closure. Optical transmission measurements on commercial fiber optic cables that were subjected to temperature cycling in an environmental chamber indicated that thermal contraction of buffer tubes at low temperature was the major contributor to fiber bending-induced loss. While the buffer tube thermal shrinkage occurs, optical fibers contained in the tube undergo nearly zero contraction. Consequently, the fibers buckle against the buffer tube inner wall, causing bending-induced losses. Cables with an initially low fiber excess length-to-buffer tube inner diameter ratio, and strong buffer tube-to-central member coupling exhibit minimal loss. It has been demonstrated in the laboratory that the low-temperature optical loss can be suppressed by effective coupling of the cable sheath to the central member.