Optical Fiber Delay Reduction via Refractive Index Profile
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Solution Overview
Problem
In long-distance communication networks, particularly submarine optical cable networks, existing optical fibers face challenges in reducing transmission delay due to geometrical and construction cost limitations, and photonic band gap fibers suffer from high transmission loss, making them unsuitable for long-distance applications.
Innovation Solution
The development of an optical fiber with a specific design featuring a core, a first clad with a low refractive index, and a second clad, optimized to achieve a mode field diameter of at least 11.5 µm and bending loss of less than 2.0 dB/100 turns, while reducing delay time to less than that of cutoff shifted fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a photonic band gap fiber with a hollow core is used to reduce delay time, then the delay time is reduced to about 3.448 μs/km, but the transmission loss increases to about several dB/km, making it unsuitable for long-distance communication
Solution Approach 1:
The patent changes the refractive index parameters of the cladding layers. Specifically, it uses a first cladding layer with refractive index n1 and a second cladding layer with refractive index n2, where n2 < n1, creating a specific refractive index profile that optimizes both delay time and transmission loss. This parameter optimization allows the fiber to achieve delay time of 4.876 μs/km or less while maintaining suitable transmission loss for long-distance communication.
2Loss of time
If the core radius is reduced to decrease delay time, then the delay time is reduced, but the mode field diameter decreases and bending loss increases
Solution Approach 1:
The patent applies local quality by creating different refractive index regions at different radial positions. The first cladding layer (with higher refractive index n1) is positioned adjacent to the core, while the second cladding layer (with lower refractive index n2) is positioned outer to the first cladding layer. This localized refractive index distribution optimizes light confinement near the core while controlling bending loss in outer regions, achieving both reduced delay time and acceptable bending loss characteristics.
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 optical fiber design achieves compatibility with existing submarine networks, significantly decreasing transmission delay in both the fiber and the overall communication system, while maintaining low bending loss and mode field diameter, thus enhancing transmission performance.
Implementation Method 1
an optical fiber includes a core, a first clad which is adjacent to an outer circumferential portion of the core and has a refractive index lower than that of the core, and a second clad which is adjacent to an outer circumferential portion of the first clad and has a refractive index lower than that of the first clad
Implementation Method 2
a refractive index difference between the core and the first clad, and a refractive index difference between the first clad and the second clad
Data Source
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AI summary
An optical fiber includes a core, a first clad that is provided on an outer circumferential portion of the core and has a refractive index lower than that of the core, and a second clad that is provided on an outer circumferential portion of the first clad and has a refractive index lower than that of the first clad. In the optical fiber, a mode field diameter at a wavelength of 1.55 µm is equal to or greater than 11.5 µm, a cutoff wavelength is equal to or less than 1.53 µm, a bending loss at a bending radius of 30 mm and a wavelength of 1.625 µm is equal to or less than 2.0 dB/100 turns, and a delay time of transmission light per unit length at a wavelength of 1.55 µm is equal to or less than 4.876 µs/km.