High Accuracy Distributed Polarization Extinction Ratio Measurement For a Polarization-Maintaining Device With Strong Polarization Crosstalk

Polarization extinction ratio (PER) is a quantitative indicator of the polarization-maintaining (PM) ability of a device. In this work, we present a distributed PER measurement method based on white-light interferometry. It can accurately measure the PER distribution of a PM device even in the presence of strong polarization crosstalk. We show that the distributed PER can be expressed as the reciprocal of the accumulated polarization crosstalk along the device. Thus, the PER distribution of a PM device can be calculated from the distributed polarization crosstalk. In the presence of strong polarization crosstalk, we introduced a concept of polarization crosstalk induced loss to prove that there is a significant error of the measured distributed polarization crosstalk. The error can be accurately estimated and be calibrated out from the measurement result. To verify the measurement method and the calibration accuracy, we used a commercial PER meter that can only measure the total PER of a device as the reference. We simulated a quasi-distributed PER device under test (DUT) by successively splicing 15 pieces of PM fibers and measured its total PER after splicing each piece of fiber. The calculated distributed PER of the DUT after error calibration matches well with the quasi-distributed result at the corresponding locations. Finally, we applied the method to measure the distributed PER and total PER of a PM fiber coil. After error calibration, the residual error (i.e., the difference with the commercial PER meter) in the total PER, thus of the distributed PER, is less than 0.1 dB.