Measuring fiber and component DGD using polarized limited-bandwidth optical sources and monitoring the DOP

We identify four methods for measuring the differential group delay (DGD) of optical fibers and discrete optical components. We generate a test signal and launch it at 45° with respect to the principal state of polarization of a device under test (DUT). After the DUT, we measure the resulting minimum degree of polarization (DOP) and relate it to the DUT´s DGD. Depending on the test signal used, along with the tone frequency-laser spacing and optical filter bandwidth, the relationship between DGD and the minimum DOP after the DUT may vary. In addition, these techniques can be used to measure the birefringence of nonmode-coupled and mode-coupled devices with a narrow transmission bandwidth. Our techniques are simple and provide flexibility in controlling the DGD measurement range and sensitivity.