IEC report provides guidance for measuring polarization crosstalk

By Hideyuki Iwata

The International Electrotechnical Commission (IEC) is soon expected to publish the first version of a guidance document for measuring the polarization crosstalk of polarization-maintaining (PM) fibers and cords for optical devices. Developed by IEC SC86A/WG1, the document called TR 62349, “Guidance for polarization crosstalk measurement of optical fibers” permits evaluation and a comparison of the crosstalk performance of various fibers.

Polarization crosstalk occurs when there’s an imperfection in the isolation between two polarizations. This report describes two methods for measuring polarization crosstalk: power method ratio and in-line.

The power ratio method pertains to fibers and connectors attached to one or both ends and to two or more such entities joined in series. This method uses the maximum and minimum values of output power at a specified wavelength.

The in-line method applies to single sections of PM fiber, cascaded PM fibers, and PM fibers interconnected with optical devices. It can also be used with PM components that lack PM fiber pigtails, in which case the measurement is performed on a PM fiber jumper connected to the output of the component. This method uses an analysis of the Poincare sphere.

The two methods yield different crosstalk values because they are based on different definitions. The power ratio method produces an “averaged” value, whereas the in-line method produces a “worst case” value.

TR 62349 is intended for manufacturers of optical fibers and components and will enable customers to compare products from different sources. The ability to measure crosstalk should lead to improvements in the performance of PM fibers and cords for optical devices such as laser diodes and modulators.