Multicore Fiber Refractive-Index Design for Short-Length Mode Control
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Solution Overview
Problem
Existing multicore fibers face issues with high-order mode propagation and crosstalk when used in short fiber lengths, particularly due to shifts in cut-off wavelengths and refractive index designs that complicate manufacturing and worsen crosstalk.
Innovation Solution
A multicore fiber design with specific refractive index differences, core diameters, and layer thickness ratios, including a glass core, glass cladding, and resin layers, to inhibit high-order mode propagation and manage crosstalk, ensuring a cut-off wavelength within specified ranges even at shorter lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench structure is adopted to inhibit high-order mode propagation, then high-order mode propagation is inhibited, but the cut-off wavelength shifts toward a longer wavelength and manufacturing complexity increases
Solution Approach 1:
The patent changes the refractive index parameter of the core portions to a specific range (0.2% ≤ Δ ≤ 0.5%) to inhibit high-order mode propagation without requiring a trench structure. This parameter optimization allows single-mode transmission even in short fibers while avoiding the complexity of trench structures.
Solution Approach 2:
The patent applies different refractive index characteristics to different regions by optimizing the core portion's refractive index relative to the cladding, creating local optical property differences that guide mode propagation without requiring physical trenches or complex structural modifications.
2Reliability
If the refractive index of core portions is increased to inhibit high-order mode propagation, then high-order mode propagation is inhibited, but crosstalk between core portions worsens
Solution Approach 1:
The patent optimizes the refractive index difference parameter to a specific range (0.2% ≤ Δ ≤ 0.5%) that simultaneously achieves high-order mode inhibition and acceptable crosstalk levels. This precise parameter control balances two competing requirements without requiring extreme refractive index values.
3Length of moving object
If fiber length is shortened for wiring applications, then installation flexibility improves, but cut-off wavelength shifts toward longer wavelength causing multi-mode transmission
Solution Approach 1:
The patent optimizes the core diameter and refractive index difference parameters specifically for short fiber applications. The core diameter range (4.0 μm to 15 μm) combined with the refractive index difference (0.2% ≤ Δ ≤ 0.5%) ensures single-mode transmission is maintained even when fiber length is shortened below 2 meters.
Solution Approach 2:
The patent applies a more conservative core diameter design than traditional long-haul fibers, using a smaller core diameter range that provides excess margin to maintain single-mode operation in short fibers where mode propagation characteristics change due to reduced length.
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 inhibits high-order mode propagation and reduces crosstalk, allowing single-mode transmission of light within the C-, O-, and L-bands even when the fiber length is shorter than 2 meters.
Implementation Method 1
when Δ denotes a maximum relative refractive-index difference of the core portions from an average refractive index of the cladding portion, Δ is in a range of 0.2% to 0.5%, inclusive
Data Source
AI summary
A multicore fiber includes: core portions; a cladding portion surrounding each core portion; a primary layer surrounding the cladding portion; and a secondary layer surrounding the primary layer. When Δ denotes a maximum relative refractive-index difference of the core portions from an average refractive index of the cladding portion, Δ is in a range of 0.2% to 0.5%, inclusive, a core diameter of each core portion is in a range of 4.0 μm to 15 μm, inclusive, a cladding diameter of the cladding portion is 125 μm or larger, a ratio of a thickness of the primary layer to a thickness of the secondary layer is 0.35 or smaller, a cut-off wavelength measured with a fiber length shorter than 2 meters is smaller than 1530 nm, and a cut-off wavelength measured with the fiber length is 1260 nm or larger.