POD Cladding Glass Layer Homogeneity via Two-Stage Process
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Solution Overview
Problem
The existing plasma outside deposition (POD) method for producing optical preforms with fluorine-doped quartz glass cladding layers faces challenges in achieving homogeneous refractive index profiles on substrate bodies with non-round cross-sections due to temperature variations, leading to inhomogeneous doping and potential bubble formation.
Innovation Solution
A two-stage POD process is employed, where a filling layer with a nominal fluorine concentration is first deposited to create a circular round cross-section, followed by a standard POD process to produce a cladding glass layer with a round outer cross-section, ensuring uniform fluorine doping and avoiding temperature-related issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard POD method is used to produce a cladding glass layer on a non-round substrate body, then the deposition process is simple, but the fluorine doping becomes inhomogeneous due to temperature variations
Solution Approach 1:
The cladding glass layer production is divided into two separate POD processes: first depositing a filling layer on the non-round substrate body, then depositing an enveloping layer on the filled substrate. This segmentation allows each layer to be optimized independently, with the filling layer compensating for temperature variations on non-round surfaces.
Solution Approach 2:
The filling layer is specifically designed with a nominal fluorine concentration that may differ from the enveloping layer. By allowing different fluorine concentrations in different regions (filling layer vs. enveloping layer), the patent achieves overall homogeneity despite local temperature variations during deposition.
2Device complexity
If the surface temperature on a non-round substrate body is allowed to vary, then the deposition process is simpler, but bubble formation increases and doping homogeneity decreases
Solution Approach 1:
The filling layer is deposited first as a preliminary step before the enveloping layer. This preliminary filling action ensures that the substrate body surface is uniformly covered and reaches a stable temperature state before the final cladding layer deposition, preventing bubble formation during the second process.
3Productivity
If a non-round cross-section is used in the substrate body, then helix modes are hindered and pump light injection is improved, but azimuthal temperature variation occurs during deposition
Solution Approach 1:
The patent changes the fluorine concentration parameter in the filling layer to compensate for the azimuthal temperature variations inherent in non-round substrate bodies. By adjusting the nominal fluorine concentration in the filling layer, the overall refractive index profile achieves homogeneity despite the non-round geometry.
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 approach results in a homogeneously doped cladding glass layer with a non-round inner and round outer cross-section, reducing mechanical stress and bubble formation risks, while maintaining high-quality boundary surfaces and efficient pump light injection in laser applications.
Implementation Method 1
a plasma burner is fed with a silicon compound, oxygen and a fluorine compound, the plasma burner being reversingly moved along the core rod rotating about its longitudinal axis
Implementation Method 2
Fluorine-doped SiO2 which is deposited layer by layer on the core glass and is thereby directly vitrified while forming the fluorine-containing SiO2 cladding glass layer is formed by reaction of the start substances in the plasma flame
Implementation Method 3
Fluorine-doped SiO2 which is deposited layer by layer on the core glass and is thereby directly vitrified while forming the fluorine-containing SiO2 cladding glass layer
Implementation Method 4
The effect of the surface temperature on the fluorine doping degree can be noticed in core rods (and generally in substrate bodies) with a non-round cross-section
Data Source
AI summary
The invention relates to a plasma deposition process for producing an optical preform, which is characterized by a cladding glass layer having a non-round internal cross-section together with high fluorine doping and axially and radially specified dopant distribution, which in the simplest case is as uniform as possible. For this purpose, a two-stage method is proposed, wherein a substrate body having a non-round cross-section is first reshaped into a coated substrate body having a circular cross-section in that a POD filling layer made of quartz glass having the nominal fluorine concentration is deposited onto a present filling surface and rounded by grinding, and then in the second stage of the method a POD sheathing glass layer made of fluorine-doped quartz glass and having a circular-ring-shaped cross-section is deposited.