scope:

INTRODUCTION

Intent.

The intent of this document is to provide an accurate method for measuring changes in the average longitudinal strain on a cabled optical fiber. It is not the purpose of this document to outline a method to statically measure absolute strain, but instead to actively measure changes in strain from one loading condition to another.

Background.

The expected reliability of optical fiber (lifetime or failure rate) may be reduced by exposure to strain that may accompany deployment in cable structures. The fiber strain can be measured during cable tensile tests by a number of methods. One common method is the phase shift technique and another is the time of flight technique. The basic principle of both measurement techniques is the determination of the change in fiber strain from a change in fiber length. The refractive index of glass changes with induced strain, which can impact the accuracy of optical fiber length measurements. Therefore, a correction factor must be determined and utilized within this procedure.

NOTE: This measurement procedure is typically performed in conjunction with the performance of FOTP-33, but such a relationship is not mandatory.