A new method is presented to determine the refractive index and the diameter of unclad optical fibers. The technique is based on an analysis of the back-scattered light when a beam from a cw laser impinges upon the fiber. A geometrical-optics analysis shows that the position of a sharp cutoff in the radiation pattern determines the refractive index, whereas the distance between certain successive minima gives the diameter. The theory is compared to experimental observations, with excellent agreement.
© 1974 Optical Society of America
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