A cable containing optical fiber ribbons in a loose tube is promising for high-density, multifiber and economical communication. This paper discusses the influence of excess fiber length.

Assuming that the optical fiber excess length (the difference between the lengths of the optical fiber and its container) causes the optical fiber to bend, the relationship between the excess length and sinusoidal bending radius has been obtained. It was found that the optical losses due to the sinusoidal bend of a graded-index multinode fiber with core and outer diameter of 50 and 125 μm respectively, were inversely proportional to the square of the minimum radius of curvature. Also, the loss characteristic is the same as that in case of the uniform spiral bend. Based on these results, the method of estimating the optical losses due to the excess length was obtained. It was confirmed that the measured optical loss agreed with the estimated loss.

It was found that the excess length ratio β should be restricted between −0.05 and 0.2 percent to minimize the optical losses and fiber failure probability.