Enhanced range for OTDR-like dispersion map measurements

We report on enhancement of the range, reliability, and accuracy of optical-time-domain-reflection- (OTDR-) like measurement of an optical fiber's dispersion map, D(z), through the combined use of Raman gain, an appropriate seed at the four-wave mixing frequency, and a greatly improved algorithm for reduction of the data. In particular, in measurements made from only one end of the fiber, we have demonstrated a range of 75 km in dispersion-shifted fiber and of 22.5 km in high-loss dispersion-compensating fiber.