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Studying polymer fiber's mechanical properties leads to an increased understanding of the behavior of polymeric structures. This will support the design of new synthetic fibers with improved properties. Thus, there is great interest in the exact knowledge of these properties. In this work, phase-shifting digital holographic interferometry is used to investigate the variation of the optical properties of drawn polyvinylidene fluoride (PVDF) fiber. The study shows that the refractive index for light which is polarized in parallel direction to the fiber axis increases as the draw ratio increases. This implicates that the molecules become more oriented in this direction. However, the decrease in the values of the refractive index for light polarized perpendicular to the drawing direction reflects the reduced orientation of the molecules in this direction. This has been confirmed by studying the variation of the molecular orientation versus birefringence of the drawn PVDF fiber. Holograms and their relationship with the optomechanical parameters obtained are given for illustration. POLYM. ENG. SCI., 51:1218-1225, 2011. [C] 2011 Society of Plastics Engineers, INTRODUCTION One property of polymeric materials is that the molecular unit, the polymer chain, can be highly anisotropic, i.e., the chain can be fully extended or curled up in an [...]