Method of controlling the index profile of optical fiber preforms

摘要

The refractive index profile of an optical fiber preform is controlled during manufacture by illuminating the gaseous precursor being fed to the preform substrate tube with ultraviolet radiation, measuring the intensity of either the uv that traverses the gas or the induced fluorescence, comparing this measurement with a reference signal, generating an error signal, in response to this comparison, and controlling composition of the gaseous precursor in response to said error signal. A similar technique can be used to control the thickness and refractive index of each layer deposited upon the substrate tube by forming an x-ray shadowgraph of the layers as they are deposited and comparing the shadowgraph characteristics with appropriate reference signals to form a second set of error signals. The latter are then used to fine tune the fabrication process. The invention can also be employed in conjunction with the vapor axial deposition method of fabricating preforms.