Backscatter measurements on optical fibers

Abstract

An optical time domain ref lectometer (OTDR) and its components are described in detail. The system performance for this device is examined. Experimental methods are described for the measurement of several parameters of interest in the characterization of optical fibers usinq the OTOR. These parameters include scatterinq loss and capture fractions for unperturbed fibers. Experimental capture-fraction values are reported for several step and qraded-index fibers and these results are compared with theoretical predictions. Rayleiqh backscatter siqnatures are also presented for several fibers from different manufacturers. Fault signatures are shown for some intrinsic and extrinsic fiber perturbations.

Characterization of a concentric-core fiber

“…Some representative backscatter signatures are shown in Figures 20 to 26. These responses yield information on fiber length, overall attenuation, length dependence of loss, and diameter variations [17]. * Three different launch conditions were used.…”

“…However, this simple relationship will not be relevant to the outer core. Experimental determinations of capture fractions can be made by a method proposed by Neumann [18] and described in detail elsewhere [17]. They are obtained from the measurement of the ratio of the power reflected from a cleaved end to the power backscattered from the fiber at that point.…”

Optical time-domain reflectometer performance and calibration studies

“…Unfortunately, many fibers encountered in practice do not obey exactly this simple exponential relationship. There are many possible reasons for this [3]. Most of these reasons have to do with the fact that some fibers (usually poor quality fibers) are not good approximations to the homogeneous transmission medium we have assumed in the derivation of eq (4-1).…”

“…From these measurements the maximum power for linear operation can be determined. The experiment was designed to test the APDs under conditions closely approximating those encountered in the time-domain reflectometer which has been described in detail elsewhere [3].…”

“…This type of noise will generally dominate in optical receivers when signal current levels are large. 3 …”