Refractive index and diameter determinations of step index optical fibers and preforms

A new method to determine the index of refraction in combination with the diameter of the cores of stepindex optical fibers and preforms is presented. The technique is based on an analysis of the backscattered light when a beam from a cw laser impinges transversely upon the fiber or preform. A geometrical-optics analysis shows that, under appropriate assumptions, a combination of the refractive indexes and the radii of the core and cladding can be determined from unique characteristics of the backscattered radiation pattern. The theory is compared to experimental observations with excellent agreement.