Abstract: The focusing method is a nondestructive one for obtaining the refractive-index profile of fibers and preforms of different sizes. An uniform incoherent collimated light beam is passed transversely through the fiber or preform immersed in an index matching oil and the light intensity distribution is directly detected by a CdS photo conductive detector, or recorded on an X-Y recorder with the aid of silicon vidicon camera and sampling line oscilloscope. The refractive-index profile is finally computed by means of a microcomputer.
This paper relates briefly the principle of the method and experimental details and also gives the quantitative results and conclusions.