Multicore Optical Fiber Core Interval Reduces DGD
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Solution Overview
Problem
In optical fiber transmission systems using multi-core fibers, excessive reduction in core interval leads to increased differential group delay (DGD) between spatial modes due to impaired linearity of core interval and mode coupling, causing accumulation of DGD, which is not effectively managed by existing technologies.
Innovation Solution
A multi-core optical fiber with a core interval setting that maintains an appropriate level of mode coupling between adjacent cores, specifically within the range of 2.6 × 10^0 to 1.6 × 10^2 [m^-1] at 1550 nm, to reduce DGD, while also considering fiber bending and torsion effects through controlled curvature and cladding structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the core interval between adjacent cores is reduced to increase core density, then the number of spatial modes increases, but the differential group delay (DGD) between spatial modes increases due to excessive mode coupling
Solution Approach 1:
The patent applies parameter changes by precisely controlling the core interval parameter to fall within a specific range (0.05Λ to 0.25Λ where Λ is the cladding diameter). This parameter optimization ensures that mode coupling remains within appropriate limits, preventing excessive DGD accumulation while maximizing the number of usable spatial modes for transmission.
Solution Approach 2:
The patent implements local quality by creating different structural characteristics in different regions of the fiber. Specifically, it introduces a trench structure surrounding each core with different refractive index properties, which locally modifies the mode coupling characteristics. This allows strong enough coupling to maintain spatial mode integrity while preventing excessive coupling that would cause DGD problems.
2Strength
If the core interval is reduced to achieve higher spatial mode coupling, then mode coupling strength increases, but random mode coupling generated by fiber bending and torsion decreases
Solution Approach 1:
The patent introduces a trench structure as an intermediary element between adjacent cores. This trench, with its distinct refractive index, acts as a mediator that controls and regulates mode coupling. It provides a controlled coupling path that maintains necessary mode interaction while filtering out random coupling effects caused by external perturbations like bending and torsion.
Solution Approach 2:
The patent employs composite material structure by combining core regions, trench regions, and cladding regions with different refractive index properties. This composite structure creates a controlled environment for mode coupling, where the trench material properties can be optimized to achieve the desired balance between controlled coupling strength and resistance to random coupling from external disturbances.
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 solution effectively reduces DGD between spatial modes, allowing for increased core density without excessive mode coupling, thereby enhancing transmission efficiency and reducing spatial mode dispersion, achieving low transmission loss and chromatic dispersion across the specified wavelength range.
Implementation Method 1
a core interval A between adjacent cores among the plurality of cores constituting the coupled-core group is set such that a mode coupling coefficient between the adjacent cores at a wavelength of 1550 nm is 2.6 × 10^0 to 1.6 × 10^2 [m^-1]
Implementation Method 2
the strength of mode coupling or power coupling between adjacent cores in a coupled-core group included in the MCF is set to an appropriate level to reduce a DGD between spatial modes
Data Source
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AI summary
The present embodiment relates to an MCF in which the strength of mode coupling or power coupling between adjacent cores included in one coupled-core group is set to an appropriate level to reduce a DGD. The MCF includes at least one coupled-core group. A core interval Λ between adjacent cores included in the coupled-core group is set such that a mode coupling coefficient between the adjacent cores at a wavelength of 1550 nm is 2.6 × 100 [m-1] to 1.6 × 102 [m-1] or a power coupling coefficient between the adjacent cores at the wavelength of 1550 nm is 1.3 × 10-3 [m-1] to 8.1 × 10° [m-1].