Optical Fiber Span with Opposite DMD Slopes
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Solution Overview
Problem
Modern high-data-rate coherent transmission systems in optical fiber communications face limitations due to fiber nonlinearities and attenuation, which restrict the achievement of higher signal-to-noise ratios (SNRs) needed for advanced modulation formats, and large effective area fibers introduce modal dispersion, limiting bandwidth and information carrying capacity.
Innovation Solution
The use of a fiber span comprising two optical fibers with specific refractive index profiles and annular claddings, where the first fiber introduces differential mode delay (DMD) for wavelengths between 1525 and 1570 nm, and the second fiber introduces DMD with an opposite sign, resulting in a total DMD less than 1.0 ps/km, minimizing modal dispersion and enhancing system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If large effective area fibers are used to carry more optical power and reduce nonlinear propagation impairments, then fiber nonlinearities decrease, but modal dispersion increases due to multiple light propagation paths
Solution Approach 1:
The fiber span is segmented into multiple fiber types (e.g., LEAF and NZ-DSF) with different DMD characteristics. Each fiber segment contributes differently to the overall modal dispersion, allowing the system to achieve low total DMD while maintaining large effective area to reduce nonlinearities.
Solution Approach 2:
The patent changes the DMD parameter by combining fibers with opposite DMD signs. By selecting fibers with complementary differential mode delay characteristics and optimizing their lengths, the system achieves low total DMD while maintaining large effective area for reduced nonlinear propagation impairments.
2Productivity
If large effective area fibers are used to increase information carrying capacity, then nonlinear propagation impairments decrease, but bandwidth is limited due to modal dispersion
Solution Approach 1:
The transmission system is divided into multiple fiber spans with different modal dispersion characteristics. By segmenting the overall transmission path and combining fibers with complementary DMD properties, the system achieves both high information carrying capacity through large effective area and high bandwidth through low total modal dispersion.
Solution Approach 2:
The patent optimizes the DMD parameter by combining fibers with opposite DMD signs and adjusts the length ratio of different fiber types to achieve low total DMD. This parameter optimization enables the system to simultaneously achieve high information carrying capacity and high bandwidth performance.
3Loss of information
If fibers with opposite DMD signs are combined to reduce total DMD, then modal dispersion decreases, but fiber span length is limited by manufacturing tolerances
Solution Approach 1:
The patent optimizes the DMD parameter by combining fibers with opposite DMD signs and adjusts the length ratio of different fiber types to achieve low total DMD. This parameter optimization enables the system to simultaneously achieve high information carrying capacity and high bandwidth performance.
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 configuration effectively reduces modal dispersion, enabling longer fiber spans and minimizing transmission losses, thus enhancing the information carrying capacity and operational reach of optical fiber communication systems.
Implementation Method 1
an annular cladding surrounding the core
Implementation Method 2
inner core region with maximum refractive index delta, Δ0≦0.1%
Data Source
AI summary
A fiber span comprising: a first optical fiber and a second optical fiber coupled to the first optical fiber, both fibers comprising the an inner core region with maximum refractive index delta, Δ0≦0.1% and an outer radius R1>4.5 μm, an outer core region with an outer radius R2 and a minimum refractive index delta Δ1 and alpha value α≧5, wherein Δ1<Δ0, 5.5 μm≦R2−R1≦12 μm; a cladding including a low index ring surrounding the core and a minimum refractive index delta ΔR,MIN<Δ1; and an outer cladding having ΔOuter-Clad>ΔR,MIN; the first fiber introducing differential mode delay DMD1 for wavelengths between 1525 and 1570 nm such that |DMD1|≦100 ps/km, and a first differential mode delay slope DMDS1; the second fiber introducing differential mode delay DMD2 for wavelengths between 1525 and 1570 nm such that |DMD2|≦100 ps/km, and a second differential mode delay slope DMDS2 that has an opposite sign from the first dispersion slope DMDS1; wherein total differential mode delay provided by the first fiber in conjunction with the second fiber is DMDtot=DMD1+DMD2, and −1.0 ps/km<DMDtot<1.0 for all wavelengths between 1525 nm and 1570 nm.