Alkali Metal Diffusion in Optical Fiber Preform Manufacturing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for doping optical fibers with alkali metals face challenges such as volatilization of alkali metals during dehydration, impurity incorporation, decreased doping efficiency, and thermal issues leading to crystal phase formation and cracking, making it difficult to achieve desirable alkali metal concentrations and low impurity concentrations in optical fibers.
Innovation Solution
A method involving the formation of an alkali-metal-doped silica glass body followed by a heat treatment to diffuse alkali metals into a silica glass body, avoiding chlorine-based dehydration and using a non-chlorine atmosphere to prevent volatilization, while forming a silica glass layer around the alkali-metal-doped core to enhance doping efficiency and reduce impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chlorine-based dehydration is used to remove impurities from silica soot, then impurity concentration is reduced, but alkali metal is volatilized and doping concentration decreases
Solution Approach 1:
The patent extracts the harmful chlorine-based dehydration step from the manufacturing process. Instead of using chlorine gas to remove impurities, the invention uses a two-stage heat treatment process that achieves impurity removal without alkali metal volatilization, thereby preserving the doped alkali metal in the core portion.
Solution Approach 2:
The patent converts the harmful effect of heat treatment (which causes alkali metal volatilization when chlorine is present) into a beneficial process by controlling the atmosphere. The heat treatment is performed in an inert or reducing atmosphere, transforming it from a harmful dehydration step into a beneficial diffusion and purification step that maintains alkali metal concentration.
2Object-affected harmful factors
If alkali metal is introduced into silica soot for doping, then Rayleigh scattering is reduced, but impurities such as transition metals are also incorporated
Solution Approach 1:
The patent uses an intermediary heat treatment process performed in a controlled inert or reducing atmosphere as a mediator between alkali metal doping and final product formation. This intermediary step allows selective removal of impurities while preserving the beneficial alkali metal dopant, achieving both low Rayleigh scattering and low impurity concentration.
3Productivity
If high temperature heat treatment is applied to diffuse alkali metal, then doping efficiency is improved, but crystal phase formation and cracking occur
Solution Approach 1:
The patent applies parameter changes by controlling the atmospheric composition (inert or reducing atmosphere) during heat treatment. This allows the process to be conducted at high temperatures for effective alkali metal diffusion without causing crystal phase formation or structural cracking that would occur in oxidizing atmospheres.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively increases alkali metal concentration and reduces impurity concentrations in the optical fiber preform, resulting in optical fibers with low transmission loss and reduced Rayleigh scattering, enabling efficient production of optical fibers with desirable properties.
Implementation Method 1
a diffusing step of diffusing the alkali metal from the alkali-metal-doped silica glass body to the silica glass body by a heat treatment
Implementation Method 2
avoiding chlorine-based dehydration and using a non-chlorine atmosphere to prevent volatilization
Data Source
AI summary
A method of producing an optical fiber preform includes a silica glass body forming step of forming a silica glass body to be at least a portion of a core portion. The method includes an alkali-metal-doped silica glass body forming step of forming an alkali-metal-doped silica glass body doped with an alkali metal around the silica glass body such that the alkali-metal-doped silica glass body contacts the silica glass body. The method further includes a diffusing step of diffusing the alkali metal from the alkali-metal-doped silica glass body to the silica glass body by a heat treatment.