Multi-core optical fiber with trench-assisted refractive index structure
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Solution Overview
Problem
Conventional multi-core fibers face challenges in achieving optical characteristics suitable for short-haul transmission while incorporating eight or more cores within a cladding diameter of 126 μm, balancing core pitch and mode field diameter to minimize crosstalk and leakage loss.
Innovation Solution
A multi-core optical fiber design featuring eight or more cores with a trench-assisted refractive index structure, where each core, inner cladding, trench, and common cladding have specific refractive index differences, and a high-index coating to suppress cladding mode propagation, allowing for a cladding diameter of not more than 126 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the core pitch is increased to reduce crosstalk, then the mode field diameter can be kept large, but the number of cores decreases or the cladding diameter increases
Solution Approach 1:
The invention divides the cladding into multiple regions, each surrounding a different core. This segmentation allows independent optimization of each core-cladding region, enabling tight core spacing (for high core density) while maintaining adequate optical isolation through region-specific refractive index profiles that prevent crosstalk between adjacent cores
Solution Approach 2:
The invention applies different refractive index profiles to different regions of the cladding. Each region has a refractive index profile specifically tailored to its local requirements, allowing the mode field diameter to be optimized locally while maintaining low crosstalk through appropriate refractive index differences between adjacent regions
2Reliability
If the core pitch is increased to reduce crosstalk, then the mode field diameter can be kept large, but the cladding diameter increases
Solution Approach 1:
By segmenting the cladding into multiple regions with distinct refractive index profiles, the invention achieves efficient space utilization. This allows the cladding to be compact (small diameter) while still providing adequate separation between cores through the refractive index barriers created by the segmented structure
Solution Approach 2:
The invention changes the refractive index parameter distribution within the cladding to achieve better space utilization. By optimizing the refractive index profiles in different regions, the invention maintains low crosstalk with shorter core pitches, thereby reducing the overall cladding diameter while preserving optical performance
3Quantity of substance
If the shortest distance between the outmost core center and the cladding surface is decreased to increase core density, then the number of cores increases, but leakage loss worsens
Solution Approach 1:
The invention applies different refractive index profiles to different regions of the cladding, allowing the outmost regions to have optimized refractive index characteristics that prevent light leakage while enabling tight core spacing. This local optimization ensures that cores can be positioned close to the cladding surface without suffering from excessive leakage loss
Solution Approach 2:
The invention introduces intermediate refractive index layers or regions between the cores and the cladding surface. These intermediate regions act as optical barriers that prevent light from leaking into the cladding, allowing cores to be positioned closer to the surface while maintaining low leakage loss through the intermediary refractive index structure
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 achieves low crosstalk and leakage loss, enabling efficient short-haul transmission with eight or more cores within the specified diameter, maintaining optical characteristics suitable for the O-band and reducing signal degradation.
Implementation Method 1
where relative refractive index differences of each core, each inner cladding, each trench, the common cladding, and the coating with respect to a predetermined refractive index are defined as Δ1, Δ2, Δ3, Δ4, and Δ5, respectively, each core, each inner cladding, each trench, the common cladding, and the coating satisfy the following conditions: Δ5 > Δ1 > Δ2 > Δ3; and Δ1 > Δ4 > Δ3
Data Source
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AI summary
An MCF of the present embodiment has eight or more cores. A diameter of a common cladding is not more than 126 µm. Optical characteristics of each core are as follows: a TL at a predetermined wavelength of 1300 nm is not more than 0.4 dB/km; an MFD at the predetermined wavelength is from 8.0 µm to 10.1 µm; a BL in a BR of not less than 5 mm or in the BR of not less than 3 mm and, less than 5 mm is not more than 0.25 dB/turn at the predetermined wavelength; λ0 is from 1300 nm to 1324 nm; λcc is not more than 1260 nm; an XT or XTs at the predetermined wavelength is not more than 0.001 /km.