Excess loss of loose tube fiber cables at low temperatures is modeled theoretically. The observed loss increase is due to random bends caused by fiber buckling as the polymer tube contracts. The derived excess loss formula for parabolic-index multimode fibers gives results in good agreement with measurements. Excess loss is in general minimized by use of small core diameter and high N.A. fibers with low frictional primary coatings. The present model shows that loose tube fiber cables can be manufactured with negligible excess loss over a wide reproducible temperature range.

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