Measurement of chromatic dispersion in optical fibers using pairs of correlated photons

Photon pairs generated by spontaneous parametric downconversion are used to implement a novel technique for measuring the chromatic dispersion of optical fibers. The time and energy correlation of the photons of a pair allow a measurement with a high time resolution which is only limited by the detection electronics. The device gives direct access to the differential group delays at several wavelengths around 1.3 μm. Our prototype setup is capable of measuring group delay differences with a resolution of about 5 ps, only limited by the upper delay limit of the time interval analyzer (presently 50 ns).