Preform for producing an optical fiber and method therefor

Abstract

The present invention provides a simple method for fabricating fiber-optic glass preforms having complex refractive index configurations and / or dopant distributions in a radial direction with a high degree of accuracy and precision. The method teaches bundling together a plurality of glass rods of specific physical, chemical, or optical properties and wherein the rod bundle is fused in a manner that maintains the cross-sectional composition and refractive-index profiles established by the position of the rods.

Description

[0001] The United States Government has rights in this invention pursuant to Contract No. DE-AC04-94AL85000 between the United States Department of Energy and Sandia Corporation for the operation of Sandia National Laboratories.BACKGROUND OF THE INVENTION [0002] The present invention is a method for fabricating fiber-optic preforms with complex refractive-index and / or dopant distributions to a high degree of accuracy and precision. In particular, the present invention focuses on the fabrication of performs for providing rare-earth-doped optical fibers such as those widely used in fiber amplifiers and lasers. [0003] The simplest method of preform fabrication is the so-called “rod-in-tube” method such as is disclosed and described in Pat. Nos. 4,668,263 and 4,264,347. A rod of glass that will form the core of the fiber is inserted into a thick-walled tube that will become the cladding, and the two are fused together at high temperature. The relative dimensions of the core and cladding...

AI Technical Summary

Benefits of technology

This approach allows for the production of optical fibers with highly controlled physical, chemical, and optical properties, overcoming the limitations of traditional methods by decoupling core and cladding indices and reducing thermal decomposition effects, resulting in improved performance and versatility in fiber designs.

Problems solved by technology

However, while simple this technique was also quite limited in its ability to implement optical fiber designs having any but the most rudimentary characteristics, and newer methods capable of producing ultra-low-loss fibers, such as are required for optical telecommunications, have essentially replaced the rod-in-tube technique.

A characteristic common to all vapor-deposition techniques is poor process control.

Delivering known and stable concentrations of dopant precursor species is particularly difficult.

In addition, these species are very reactive, making it difficult to use mass-flow controllers or similar devices to regulate reactant flow rates and therefore rates of species addition.

Similarly, with the solution doping technique, the distribution of dopant species incorporated into the host material is often non-uniform and unpredictable (the density and pore size of the partially sintered glass network can vary substantially).

As a result, the range of fiber designs that can be fabricated is quite limited.

This limitation persists despite large investments of time and resources in the development of optical fibers for a wide variety of commercially significant applications {see S. E. Miller and A. G. Chynoweth eds., Optical Fiber Telecommunications (Academic Press, San Diego, Calif., 1979); P. C. Becker, N. A. Olsson, and J. R. Simpson, Erbium-Doped Fiber Amplifiers (Academic Press, San Diego, Calif., 1999)}.

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