Measurement of group velocity dispersion in optical fiber with a hundreds of meters lengths

In this work an experimental setup that allows evaluating the group velocity dispersion (GVD) in optical fibers with a hundreds of meters length is presented. The setup was composed by an optical fiber Sagnac Interferometer, SI. The optical fiber under test and a phase modulator were placed inside of the SI loop. The main idea is to place asymmetrically the phase modulator inside the SI loop. This means that the fiber length in both sides of the phase modulator, L1 and L2, satisfy L1<<L2. This unbalance allows evaluating the GVD due to the fact that contra-propagating beams travel with different propagation constants. With this technique it was possible to measure GVD with a picosecond temporal resolution without using a fast detector or wide band-width equipment. Results of GVD measurement performed with the developed algorithm are presented.