Intra-cavity fiber laser technique for high accuracy birefringence measurement

When a device under test (DUT) with birefringence is placed within a laser cavity two distinct sets of orthogonally polarized longitudinal modes will result. If the output of the laser is sent through a 45(o) linear polarizer, polarization mode beating (PMB) between these two sets of longitudinal modes can be detected. We demonstrate the relation between PMB and the birefringence of the DUT and show that by tracking the PMB it provides a sensitive measurement of the birefringence of the device. We first examined the birefringence of a Newport PM fiber and then measured the birefringence of a 3M (Austin, TX) Chirped grating 1.0 m in length. For comparison, birefringence measurements were performed using a Hewlett-Packard Polarization Analyzer (HP 8509B).