Graded-Index Multimode Optical Fiber Bending Loss Reduction
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Solution Overview
Problem
Multimode optical fibers experience significant bending losses and increased mode partition noise when subjected to bends, particularly in high-speed applications like 10 GbE systems, due to the varying propagation times of different modes, which limits their bandwidth and data transmission efficiency.
Innovation Solution
A silica-based multimode optical fiber with a graded-index core and a constant outer cladding, where the minimum optical index of the core is greater than the cladding index, reducing bending losses by increasing the effective refractive index of guided modes and maintaining compatibility with standard graded-index fibers, thus minimizing the impact of bends on data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If a standard graded-index multimode fibre is used, then the bandwidth is improved, but bending losses increase significantly
Solution Approach 1:
The patent modifies the refractive index parameters by setting the minimum core index n_min to be greater than the cladding index n_cladding (specifically n_min - n_cladding between 2x10^-3 and 10x10^-3), rather than using the conventional n_min = n_cladding. This parameter change fundamentally alters the mode propagation characteristics, making the fibre less sensitive to bending while preserving bandwidth through the graded-index profile with parameter α between 1.9 and 2.2
2Loss of energy
If the minimum optical index of the core is increased above the cladding index, then bending losses are reduced, but compatibility with standard fibres deteriorates
Solution Approach 1:
The patent carefully selects the parameter range for n_min - n_cladding (between 2x10^-3 and 10x10^-3) and the graded-index parameter α (between 1.9 and 2.2) to achieve an optimal balance. These specific parameter ranges reduce bending losses while maintaining sufficient mode coupling with standard fibres for practical compatibility in network installations
3Ease of operation
If bends are applied to the fibre, then ease of installation is improved, but mode partition noise increases
Solution Approach 1:
The patent implements preliminary anti-action by designing the refractive index profile with n_min > n_cladding before the fibre is installed and bent. This pre-configured index profile creates a protective effect that counteracts the harmful impact of subsequent bending, reducing mode partition noise generation even when the fibre is subjected to installation bends
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 proposed fiber design achieves reduced bending losses of less than 0.1 dB per two turns for a radius of curvature of 15 mm, enhancing data transmission reliability and efficiency, particularly in local area networks, with a data rate of 10 Gb/s up to 300 m, while maintaining compatibility with standard graded-index fibers.
Implementation Method 1
the refractive indices of the optical core n core and of the outer optical cladding n cladding are such that n core >n cladding
Implementation Method 2
an outer optical cladding having the function of confining the optical signal within the optical core
Data Source
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AI summary
The present invention relates to a multimode optical fibre comprising from the centre to the periphery an optical core and a cladding having a refractive index defined by ncladding, wherein the core has a radius (r1) and an α refractive index profile with a graded index with respect to the cladding, the maximum refractive index of the core being nmax and the minimum refractive index of the core being nmin, in which nmin - ncladding > 2x10-3, the fibre exhibiting a bending loss of less than 0.1 dB for two turns for a radius of curvature of 15 mm. The cladding is in direct contact with the core. The invention thus makes it possible to obtain a graded-index fibre having reduced bending losses with coupling losses to a standard graded-index fibre which are more limited than in the state of the art.