Optical Fiber Preform With Segmented Cladding For Alkali Metal Diffusion Control
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Solution Overview
Problem
Existing optical fiber preforms face challenges in maintaining a high concentration of alkali metal elements during the drawing process, leading to increased attenuation and reduced productivity due to diffusion issues and crystallization problems.
Innovation Solution
An optical fiber preform composed of silica-based glass with a core portion containing an alkali metal concentration of 5 atomic ppm or more, a first cladding portion with high OH group concentrations, and a second cladding portion, where the first cladding portion has an outside diameter of 30 µm to 45 µm and is made transparent by sintering silica glass soot, effectively limiting alkali metal diffusion and maintaining high alkali metal concentrations in the core.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the core portion is doped with alkali metal element to reduce viscosity and relaxation, then attenuation can be reduced, but diffusion of alkali metal during drawing causes loss of concentration control
Solution Approach 1:
The cladding is divided into two portions: a first cladding portion with high OH group concentration (200-2000 mol ppm) that acts as a diffusion barrier, and a second cladding portion with low OH group concentration that provides optical transmission. This segmentation allows the first cladding to prevent alkali metal diffusion while the second cladding maintains optical performance.
Solution Approach 2:
The first cladding portion is designed with locally high OH group concentration specifically at the interface with the core, creating a diffusion barrier only where needed. The OH group concentration is controlled to be 200-2000 mol ppm in the first cladding but kept low (0.01-10 mol ppm) in the core and second cladding, providing localized functionality without compromising overall optical performance.
2Stability of the object's composition
If the first cladding portion has high OH group concentration to limit alkali metal diffusion, then alkali metal concentration in core is maintained, but OH groups cause attenuation increase
Solution Approach 1:
The cladding is segmented into two portions with different OH group concentrations. The first cladding portion has high OH group concentration (200-2000 mol ppm) to act as a diffusion barrier, while the second cladding portion has low OH group concentration (0.01-10 mol ppm) to minimize attenuation. This segmentation allows the system to achieve both diffusion barrier functionality and low attenuation.
Solution Approach 2:
High OH group concentration is localized only to the first cladding portion at the core-interface region where diffusion barrier function is needed. The second cladding portion maintains low OH group concentration to ensure optimal optical transmission. This localized quality distribution resolves the contradiction between diffusion barrier needs and attenuation control.
3Reliability
If the optical fiber preform is drawn to achieve sufficient alkali metal concentration in core, then attenuation is reduced, but drawing process complexity and productivity are affected
Solution Approach 1:
The first cladding portion is pre-formed with high OH group concentration (200-2000 mol ppm) before the drawing process. This preliminary preparation creates a diffusion barrier that maintains alkali metal concentration in the core during drawing, eliminating the need for complex post-drawing treatment and simplifying the overall manufacturing process.
Solution Approach 2:
The OH group concentration parameter is optimized to be 200-2000 mol ppm in the first cladding portion, which provides sufficient diffusion barrier functionality while maintaining drawability. This parameter optimization allows the fiber to be drawn efficiently without requiring excessive alkali metal concentration or complex processing steps.
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 configuration results in an optical fiber with reduced attenuation, specifically 0.185 dB/km at 1,550 nm and 0.80 dB/km at 1,380 nm, while maintaining a sufficient alkali metal concentration in the core, thereby improving productivity and reducing scattering losses.
Implementation Method 1
The alkali metal element diffuses faster than the transition metal element. Therefore, even when some thickness of glass surface is etched to remove the transition metal element, it is possible to allow the alkali metal element to remain.
Implementation Method 2
The second cladding portion may be made transparent by sintering a silica glass soot synthesized in a vapor phase on the perimeter of the first cladding portion.
Implementation Method 3
The concentration of the OH group in the perimeter portion of the first cladding is calculated by: OH group concentration ppm=A/6200×dmm/×107 ppm on the basis of an increment A of absorbance of infrared light from the base line on the first cladding side
Data Source
AI summary
An easily producible optical fiber preform which is drawn to an optical fiber having a core containing a sufficient concentration of alkali metal is provided. An optical fiber preform 10 is composed of silica-based glass and includes a core portion 20 and a cladding portion 30. The core portion 20 includes a first core portion 21 including a central axis and a second core portion 22 disposed on the perimeter of the first core portion 21. The cladding portion 30 includes a first cladding portion 31 disposed on the perimeter of the second core portion 22 and a second cladding portion 32 disposed on the perimeter of the first cladding portion 31. The core portion 20 contains an alkali metal at an average concentration of 5 atomic ppm or more. The concentration of the OH group in the perimeter portion of the first cladding portion 31 is 200 mol ppm or more.