IEC offers guidance on residual stress

The International Electrotechnical Commission (IEC) is expected to soon publish the first version of a technical report that gives guidance for measuring the residual stress in an optical fiber. Developed by IEC SC86A/WG1, the document TR 62469, “Guidance for Residual Stress Measurement of Optical Fibre,” explains the principle and gives detailed procedures for obtaining a fiber’s residual stress profile. It also shows a method to obtain a tomographic stress distribution for an optical fiber with a nonsymmetric structure. Unlike IEC standards, the purpose of technical reports is to provide guidance and information on topics and parameters that are not intended to be specified.

Residual stress in an optical fiber is induced during high speed and high tension drawing. The measurement of residual stress distribution is considered to be important information as it affects critical fiber parameters, such as refractive index, intrinsic polarization-mode dispersion, mode field diameter, chromatic dispersion, curl, and the effect of temperature changes.

The technical report describes an optical transverse phase retardation measurement method in which a polariscope is used for determining residual stresses. Stressed material shows stress-induced birefringence for light propagating through it. By measuring polarization-dependent phase retardation of transmitted light through an uncoated fiber sample a few centimeters long, the amount of residual stress is obtained.

TR 62469 is intended for manufacturers of optical fibers and component manufacturers so that they have a uniform procedure for measuring the residual stress of their products. It will help them develop a better fabrication process with lower or higher residual stress. Customers or cable companies can compare fibers from different suppliers by evaluating their residual stress profiles. This ability would provide additional information regarding the quality of an optical fiber for special applications.

Dug Young Kim (dykim@gist.ac.kr) is a member of IEC SC86A/WG1 and is at Gwangju Institute of Science and Technology (GIST), in South Korea. He is doing research on various optical techniques for characterizing optical fibers and fiber devices.

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