Multi-core Fiber Crosstalk Suppression via Refractive Index Control
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Solution Overview
Problem
Multi-core fibers experience significant crosstalk between adjacent cores, especially when nonlinearly disposed, leading to increased splicing losses and reduced communication quality due to mismatched propagation constants, particularly at smaller bending radii.
Innovation Solution
A multi-core fiber design with an even number of six or more cores, featuring two types of cores with alternating effective refractive indices, disposed in a regular polygon configuration, and a specific refractive index difference to maintain a mode field diameter difference of 1 µm or less, effectively managing the effective refractive index difference between 1.450 × 10^-5 × D ≤ Δn eff ≤ 0.002, where D is the core pitch, to suppress crosstalk and splicing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the propagation constants of adjacent cores are varied to reduce crosstalk, then crosstalk is reduced, but splicing losses increase due to mode field diameter mismatch
Solution Approach 1:
The patent applies parameter changes by precisely controlling the effective refractive index difference between adjacent cores within a specific range (0.0005 ≤ Δn eff ≤ 0.002). This parameter optimization allows the fiber to maintain different propagation constants for crosstalk suppression while keeping mode field diameter differences minimal (1 μm or less) to reduce splicing losses.
Solution Approach 2:
The patent introduces dynamic bending radius design where the fiber is configured to have different bending radii in different sections. By setting the bending radius in the second section to be smaller than in the first section, the patent dynamically adjusts the propagation constants during signal transmission, ensuring they remain different to suppress crosstalk while maintaining connection efficiency.
2Volume of moving object
If the bending radius is reduced to accommodate fiber in cables, then fiber accommodation is improved, but crosstalk increases when propagation constants become matched
Solution Approach 1:
The patent uses dynamic bending radius design where different sections of the fiber have different bending radii. The second section has a smaller bending radius (50-100 mm) compared to the first section (100-200 mm), which dynamically adjusts propagation constants to remain different even at small bending radii, preventing crosstalk while enabling compact cable accommodation.
Solution Approach 2:
The patent changes the effective refractive index parameter between adjacent cores within a controlled range (0.0005 ≤ Δn eff ≤ 0.002), which shifts the bending radius at which crosstalk peaks to a value smaller than the minimum bending radius (100 mm) used in practical cable installations. This parameter optimization allows safe operation at small bending radii without crosstalk.
3Object-affected harmful factors
If the mode field diameter difference is increased to suppress crosstalk, then crosstalk is reduced, but splicing losses increase
Solution Approach 1:
The patent optimizes the effective refractive index difference parameter within a specific range (0.0005 ≤ Δn eff ≤ 0.002) to achieve the right balance: it creates sufficient propagation constant differences to suppress crosstalk while keeping mode field diameter differences minimal (1 μm or less) to ensure low splicing losses during fiber connections.
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 effectively suppresses crosstalk and splicing losses even at smaller bending radii, maintaining communication quality while allowing for efficient connection of multi-core fibers with minimal attenuation, as the effective refractive index difference ensures the bending radius at which crosstalk peaks is reduced below the typical minimum bending radius of 100 mm.
Implementation Method 1
an outer periphery of one core is surrounded by a clad, and information is transmitted when an optical signal propagates in this core
Implementation Method 2
refractive index differences are changed between the clad and cores adjacent to each other to vary the propagation constants (the wave guide conditions) of the cores adjacent to each other
Data Source
Figure 1A~1B
Figure 2~3
Figure 4~5
AI summary
There is provided a multi-core fiber that can suppress the crosstalk between cores adjacent to each other even in the case where the multi-core fiber is nonlinearly disposed while suppressing splicing losses. A multi-core fiber (1) includes an even number of six or more of cores and a clad (20) that surrounds the outer circumferential surfaces of the cores. The cores are formed of two types of cores (11) and (12) in which an effective refractive index difference in a fundamental mode is 0.002 or less in a predetermined range or more that the effective refractive index difference in the fundamental mode is varied according to a core pitch. Two types of the cores (11) and (12) are alternately and annularly disposed at regular spacings. A difference in the mode field diameter of light propagating through the cores (11) and (12) is 1 µm or less.