Method for making a preform for optical fibers by drawing a mother ingot

摘要

A method for drawing a mother ingot into a preform for optical fibers comprises providing a mother ingot, subjecting the mother ingot to measurement of a distribution of refractive index along radial directions thereof to determine a ratio of a core diameter to a clad diameter, and comparing the thus determined ratio with a predetermined ratio between the core diameter and the ingot diameter which ensures intended optical transmission characteristics, under which if the determined ratio is insufficient for the intended light transmission characteristics, the mother ingot is further processed until the predetermined ratio is substantially attained, and the resultant ingot is drawn to a preform, or if the determined ratio is acceptable on comparison with the predetermined ratio, the mother ingot is finally drawn.