Decay of transmitted light during fiber breaks-implications for break location

The accuracy of a bit-counting method for locating fiber breaks in an optical communication system proposed by Rosher et al. is limited in part by the decay time of the transmitted light during fiber failure. In order to understand the nature of this limitation, decay times were measured for individual fibers using a variety of failure mechanisms. The mechanics of the break processes were considered and the implications for break location using the bit-counting technique were assessed. The fastest decay times (≈14 ns) occurred when fibers broke catastrophically under stress levels greater than 0.7×109 N/m². The decay times in this case implied a small break-location uncertainty of 3 m when employing the bit-counting scheme. Since the strength members of fiber cable break at much greater tensions, decay times for cable failures (for example, caused by a backhoe) should not significantly limit the break-location accuracy assuming that the fibers do not bend severely before breaking. For stresses below 0.7×109 N/m² the decay times increase as the stress decreases, attributable to a corresponding decrease in the speed with which the cores of the broken fiber sections tilt with respect to each other and/or separate