High Precise Time Delay Measurement in Optical Fiber

Due to its properties of low attenuation, high capacity and reliability, the widespread optical fiber network has become an attractive option for long-distance transmission. The signal transmission delay in fiber, as an essential characteristic, becomes a significant parameter that has broad effects on the performance of optical communications, fiber timing distribution systems, phased array antennas, and some other large-scale scientific or engineering facilities. We report a novel method for signal transmission delay measurement in optical fibers. Based on phase discrimination, dual-frequency locking and measurement, it achieves a very high measurement precision of 0.2 ps with a 0.1 ps resolution, and dynamic range over 50 km. Using a phase shift and frequency locking technique, the measurement ambiguity can be resolved within only a few seconds. It greatly simplifies the measurement procedure and requires much simpler equipment. A good agreement in measurement results with the conventional pulsed method is obtained as well.