Optical Fiber Preform Core Doping for Attenuation Reduction
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Solution Overview
Problem
Existing optical fiber preforms fail to maintain a sufficient concentration of alkali metal elements in the core, leading to inadequate reduction in attenuation due to diffusion issues during the drawing process, resulting in insufficient reduction of Rayleigh scattering loss.
Innovation Solution
An optical fiber preform design featuring a core with a first region containing a high diffusion coefficient dopant like sodium or potassium and a second region with a low diffusion coefficient dopant such as Rb, Cs, Mg, or Sr, where the second dopant has a concentration of 10 atomic ppm or more and a diffusion coefficient of 1×10−12 cm2/s or more at 2,000° C. to 2,300° C., ensuring a high concentration of alkali metal elements in the core center and a controlled concentration distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single dopant type is used in the core portion, then the manufacturing process is simple, but the concentration distribution of alkali metal elements cannot be uniformized during drawing, resulting in high attenuation
Solution Approach 1:
The core portion is divided into two regions with different dopant characteristics: a first region containing a first dopant (e.g., Na, K) with high diffusion coefficient, and a second region containing a second dopant (e.g., Rb, Cs, Mg, Ca, Sr) with low diffusion coefficient. This local differentiation enables controlled diffusion during drawing to achieve uniform alkali metal distribution and reduce attenuation.
Solution Approach 2:
The optical fiber preform uses a composite doping strategy combining two types of dopants with different diffusion coefficients in the core portion. This composite approach leverages the complementary properties of both dopant types to achieve optimal concentration distribution and minimize energy loss during the drawing process.
2Loss of energy
If alkali metal elements are added to reduce viscosity and uniformize network structure, then Rayleigh scattering loss is reduced, but the concentration distribution becomes non-uniform during drawing, increasing attenuation
Solution Approach 1:
The invention changes the diffusion coefficient parameter by selecting dopants with different diffusion characteristics. The first dopant has a high diffusion coefficient to enable rapid diffusion during drawing, while the second dopant has a low diffusion coefficient to maintain stability. This parameter differentiation ensures both viscosity reduction and uniform concentration distribution.
3Strength
If the core portion contains high concentration of alkali metal elements, then viscosity is reduced and network structure is uniformized, but crystallization occurs during fiber drawing
Solution Approach 1:
By dividing the core into two regions with different dopant types, the invention achieves local optimization: the first dopant provides strong viscosity reduction effect, while the second dopant acts as a crystallization inhibitor. This local quality differentiation maintains the amorphous structure during drawing while achieving the desired viscosity characteristics.
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 design achieves a significantly low attenuation of 0.160 dB/km at 1,550 nm by maintaining a high concentration of alkali metal elements in the core center, where the fundamental-mode light power is highest, effectively reducing Rayleigh scattering and ensuring successful fiber drawing without crystallization issues.
Implementation Method 1
The second dopant having a diffusion coefficient of 1×10−12 cm2/s or more and less than the first dopant at a temperature of 2,000° C. to 2,300° C.
Implementation Method 2
the second dopant that reduces viscosity of the silica glass
Implementation Method 3
The incorporation of an alkali metal element in a core portion of an optical fiber preform can reduce the viscosity of the core portion when the optical fiber preform is drawn, thus uniformizing the network structure of a silica glass to reduce the Rayleigh scattering loss
Implementation Method 4
when the optical fiber preform is drawn
Data Source
AI summary
An optical fiber preform includes a silica-glass core portion, and a cladding portion surrounding the core portion, the cladding portion being composed of a fluorine-containing silica glass having a lower refractive index than the core portion, the core portion including a first region that does not include the central axis thereof, the first region containing a first dopant selected from sodium, potassium, and compounds thereof, and a second region that includes the central axis, the second region containing a second dopant that reduces the viscosity of the silica glass, the second dopant having a diffusion coefficient of 1×10−12 cm2/s or more and less than the first dopant at 2,000° C. to 2,300° C., in which the entire core portion has an average first dopant concentration of 10 atomic ppm or more and 2,000 atomic ppm or less and an average second dopant concentration of 10 atomic ppm or more.