Multicore Fiber Low Refractive Index Cladding for DMGD Reduction
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Solution Overview
Problem
Conventional multicore fibers face limitations in reducing differential mode group delay (DMGD) due to broad core pitches, which compromise spatial efficiency and increase crosstalk, necessitating a solution to mitigate DMGD with narrower core pitches.
Innovation Solution
A multicore fiber design featuring two or more cores arranged in a circular shape with a low refractive index portion, either as a hole or solid, within the cladding, to reduce the difference in effective refractive indices among super-modes, thereby enhancing mode coupling and reducing DMGD even at narrower core pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the core pitch is broadened to reduce the difference of effective refractive indices among super-modes, then the differential mode group delay (DMGD) can be mitigated, but the spatial efficiency decreases and crosstalk among cores increases
Solution Approach 1:
The patent introduces a low refractive index portion (hole or solid structure) at specific locations within the cladding region, creating local refractive index variations. This local modification changes the effective refractive indices of super-modes differently, reducing the Δneff among them without requiring overall core pitch broadening, thus maintaining spatial efficiency while mitigating DMGD
Solution Approach 2:
The patent modifies the refractive index parameter of the cladding by introducing a low refractive index portion (where n3 < n2). This parameter change in the cladding region directly affects the effective refractive indices of super-modes, enabling DMGD mitigation through controlled refractive index engineering rather than geometric pitch adjustment
2Area of stationary object
If the core pitch is narrowed to improve spatial efficiency, then more cores can be packed, but the difference of effective refractive indices among super-modes increases leading to higher DMGD
Solution Approach 1:
By placing low refractive index portions at specific locations in the cladding, the patent creates localized field confinement effects that enhance coupling among closely-spaced cores. This local modification compensates for the reduced pitch, maintaining effective mode coupling and DMGD performance even when cores are narrowly spaced for better spatial efficiency
Solution Approach 2:
The low refractive index portion acts as an intermediary structure that mediates the optical field interaction between closely-spaced cores. It provides a controlled coupling mechanism that enables effective super-mode formation and DMGD mitigation without requiring large core pitch separation
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 reduces DMGD and enhances spatial efficiency by allowing for narrower core pitches while maintaining equivalent or better performance compared to conventional fibers, thereby improving communication capacity and reducing signal processing burdens.
Implementation Method 1
a low refractive index portion having a refractive index lower than a refractive index of the cladding... reduce the difference of effective refractive indices (neff) among the super-modes
Data Source
AI summary
A multicore fiber including two or more cores each capable of single mode transmission, a cladding covering around the two or more cores in common, and a low refractive index portion having a refractive index lower than a refractive index of the cladding, wherein a cross-section perpendicular to a longitudinal direction includes a region where two or more cores of a part or all of the two or more cores are arranged in a circular shape and at least a part of the low refractive index portion is arranged inside an inscribed circle of the cores included in the region.