Coupled Multi-Core Fiber Reducing Transmission Loss
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Solution Overview
Problem
Conventional multi-core optical fibers face challenges in reducing transmission loss due to the diffusion of alkali metal elements during the drawing process, which limits the concentration of alkali metal in the core, leading to increased crystallization and crosstalk between closely arranged cores, thereby restricting the reduction of transmission loss.
Innovation Solution
A coupled multi-core optical fiber design with a reduced core pitch to actively generate inter-core crosstalk, combined with MIMO processing, allows for efficient diffusion of alkali metal between adjacent cores, maintaining optical coupling and achieving lower transmission loss by setting the power coupling coefficient and stress profile to specific values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If alkali metal is added to the core to reduce transmission loss, then transmission loss is reduced, but alkali metal diffuses during drawing, reducing concentration and limiting structural relaxation
Solution Approach 1:
The patent applies preliminary action by adding alkali metal to the preform before the drawing process. This allows the alkali metal to be present in the core structure from the beginning, enabling it to contribute to structural relaxation during drawing while maintaining sufficient concentration for loss reduction. The preform preparation stage is used to establish the optimal alkali metal distribution before the diffusion-prone drawing process begins.
Solution Approach 2:
The patent employs parameter changes by optimizing the alkali metal concentration within a specific range (0.2-50 atom ppm, preferably 5-50 atom ppm). This controlled parameter adjustment ensures that there is enough alkali metal to reduce transmission loss and enable structural relaxation, while preventing excessive concentration that would cause crystallization. The concentration parameter is carefully tuned to balance multiple competing requirements.
2Productivity
If core pitch is reduced to enable mode division multiplex transmission, then spatial density is improved, but crosstalk occurs between adjacent cores
Solution Approach 1:
The patent converts the harmful effect of crosstalk into a beneficial feature by intentionally designing the core pitch to generate controlled inter-core crosstalk. This controlled crosstalk, combined with MIMO processing, enables mode division multiplex transmission. The previously problematic crosstalk is transformed into a mechanism that facilitates higher spatial density and increased transmission capacity.
Solution Approach 2:
The patent applies parameter changes by optimizing the core pitch to a specific range that enables both high spatial density and controlled crosstalk generation. The core pitch is reduced compared to conventional fibers, but maintained at a level that allows beneficial coupling for mode division multiplexing when combined with MIMO processing.
3Stability of the object's composition
If alkali metal concentration is increased to suppress crystallization, then structural stability is improved, but diffusion during drawing reduces the concentration
Solution Approach 1:
The patent uses preliminary action by adding the required alkali metal concentration to the preform before drawing. This ensures that the core structure has sufficient alkali metal from the outset to maintain stability and prevent crystallization during the drawing process. The preform is prepared with the optimal concentration that accounts for subsequent diffusion losses.
Solution Approach 2:
The patent applies parameter changes by maintaining the alkali metal concentration within an optimized range (0.2-50 atom ppm) that balances structural stability with resistance to diffusion losses. This parameter control ensures that enough alkali metal remains after drawing to prevent crystallization and maintain core structure integrity.
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
The design effectively reduces transmission loss by maintaining a high alkali metal concentration and suppressing diffusion-induced losses, achieving lower transmission loss compared to non-coupled fibers while maintaining a small differential group delay.
Implementation Method 1
alkali metal elements are easily diffused in comparison with other elements, and the alkali metal concentration in the core in the optical fiber reduces in comparison with the concentration in a preform, during drawing from the preform to the optical fiber
Implementation Method 2
a maximum value σmax of stress profile on a line segment connecting centers of the adjacent cores has a negative value (compressive stress)
Data Source
AI summary
The present embodiment relates to a CMCF including a structure to achieve more efficient reduction in transmission loss by suppressing decrease in concentration of alkali metal due to diffusion of alkali metal. In the CMCF including a plurality of cores, a power coupling coefficient h between adjacent cores is set to 1×10−3/m or more, to maintain an optical coupling state between the adjacent cores. In addition, alkali metal contributing to reduction in transmission loss is added to each of the cores such that a stress maximum value σ_<sup2>max </sup2>between adjacent cores has a negative value.