Optical Fiber Multi-Layer Cladding Bending Loss MFD Trade-off
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Solution Overview
Problem
Low bending loss optical fibers used in small-diameter and high-density cables face a trade-off with reduced mode field diameter (MFD), leading to mismatch issues when connected to general-purpose single-mode fibers, causing losses and inspection difficulties.
Innovation Solution
An optical fiber design with a specific refractive index profile and cladding structure, including an inner and outer cladding layer, is implemented to minimize bending loss while maintaining a suitable MFD, characterized by refractive index relationships and radii that satisfy certain conditions to ensure compatibility with standard single-mode fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the refractive index of the core region is increased to reduce bending loss, then bending resistance is improved, but the mode field diameter (MFD) is reduced
Solution Approach 1:
The cladding is divided into multiple layers (first cladding layer adjacent to core, second cladding layer on outer circumference, and optionally third cladding layer) with different refractive index characteristics. This segmentation allows independent optimization of bending loss (through inner layers) and MFD (through outer layers), resolving the trade-off between bending resistance and mode field diameter.
Solution Approach 2:
Different regions of the cladding are assigned different refractive index properties: the inner cladding layer has higher refractive index to reduce bending loss, while the outer cladding layer has lower refractive index to maintain larger MFD. This local differentiation of optical properties enables simultaneous achievement of both bending resistance and compatible MFD.
2Quantity of substance
If a small-diameter and high-density cable structure is adopted to increase packaging density, then cable compactness is improved, but local bending is applied to optical fiber causing increased bending loss
Solution Approach 1:
The multi-layer cladding structure with distinct refractive index zones enables the optical fiber to withstand the local bending stresses inherent in compact cable designs. The inner high-refractive-index layer provides bending loss suppression while the overall fiber structure maintains compatibility with high-density packaging requirements.
3Reliability
If the mode field diameter is reduced to improve bending loss characteristic, then bending resistance is improved, but mismatch occurs when connected to general-purpose single-mode fiber causing connection loss
Solution Approach 1:
The optical fiber design implements local quality differentiation in the cladding: inner layers with higher refractive index suppress bending loss, while outer layers with lower refractive index maintain a larger mode field diameter (8.6-9.2 μm at 1310 nm) that matches general-purpose single-mode fibers, thereby eliminating connection loss while preserving bending resistance.
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 reduced bending loss while preserving the MFD, enabling the optical fiber to be used in small-diameter and high-density cables without causing mismatch, thus allowing for space-saving and reliable connectivity.
Implementation Method 1
light confined in a core of an optical fiber leaks out of the core due to bending
Implementation Method 2
a refractive index of the core is Δ1, a maximum refractive index of the core is Δ1max, and an outer circumference radius of the core is r1, a refractive index of the inner cladding layer is Δ2
Data Source
AI summary
An optical fiber includes: a core; and a clad which is formed so as to surround an outer circumference of the core concentrically with the core, the clad having at least an inner cladding layer adjacent to the outer circumference of the core and an outer cladding layer formed on an outer circumference of the inner cladding layer, wherein a refractive index of the outer cladding layer is Δ3, and an outer circumference radius of the outer cladding layer is r3, a relationship of Δ1max>Δ3>Δ2min is satisfied, a relationship of Δ3−Δ2min≤0.08% is satisfied, a relationship of r1<r2<r3 is satisfied, a relationship of 0.35≤r1/r2≤0.55 is satisfied, a cable cut-off wavelength is less than or equal to 1260 nm, and an MFD at a wavelength of 1310 nm is 8.6 μm to 9.2 μm.