Multi-core Erbium-doped Fiber Crosstalk Suppression
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Solution Overview
Problem
Multi-core Erbium-doped fiber amplifiers (EDFAs) experience signal light quality deterioration due to inter-core crosstalk, which is typically around -20 dB to -25 dB, affecting signal transmission quality.
Innovation Solution
A multi-core amplification optical fiber with core portions doped with rare-earth elements, specifically erbium, and a cladding portion with a relative refractive index difference of 0.5% to 2% and core diameters of 1 µm to 5 µm, where the separation distance between core portions is set to achieve crosstalk of -30 dB or lower, and the erbium doping concentration is differentiated to optimize signal amplification and noise figure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-core Erbium-doped fiber amplifier is used for signal amplification, then transmission capacity is improved, but inter-core crosstalk causes signal light quality deterioration
Solution Approach 1:
The patent applies local quality by creating distinct core regions with different doping concentrations and structural characteristics. Each core portion has optimized local properties (erbium concentration, refractive index profile) to minimize inter-core interference while maintaining amplification functionality, thereby reducing crosstalk and improving signal quality in multi-core amplifiers
Solution Approach 2:
The patent introduces an intermediary structure between cores, specifically the cladding portion with optimized refractive index and the hole structure, which acts as a barrier to reduce optical coupling between adjacent cores. This intermediary layer suppresses crosstalk while allowing each core to function independently for signal amplification
2Power
If core diameter is increased to improve signal power, then amplification gain is improved, but crosstalk between cores increases
Solution Approach 1:
The patent employs parameter changes by optimizing the core diameter within a specific range (1 µm to 5 µm) and adjusting the erbium doping concentration accordingly. This parameter optimization allows the core to maintain sufficient signal power for effective amplification while keeping the core size small enough to minimize evanescent field overlap and crosstalk between adjacent cores
3Power
If erbium doping concentration is increased to improve gain, then amplification performance is improved, but noise figure increases
Solution Approach 1:
The patent applies local quality by implementing differentiated erbium doping concentrations across different core portions. Some cores have higher doping levels optimized for gain, while others have lower doping levels optimized for low noise figure, allowing each core to be tailored for specific performance requirements within the multi-core amplifier system
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 solution effectively suppresses signal light quality degradation by achieving crosstalk levels of -30 dB or lower, providing a gain of 15 dB or higher and a noise figure of 7 dB or lower, thereby enhancing the quality of signal transmission.
Implementation Method 1
a plurality of core portions doped with a rare-earth element... when a concentration of the rare-earth element doped to each of the core portions is 250 ppm to 2000 ppm... the signal light is amplified optically so that a gain is equal to or higher than 15 dB
Implementation Method 2
an inner cladding portion positioned at a periphery of the plurality of core portions, having a refractive index lower than a refractive index of the plurality of core portions... a separation distance of each of the core portions from adjacent one of the core portions is set at equal to or larger than 30 µm and at equal to or smaller than 60 µm so that a crosstalk of light between the adjacent core portions is equal to or lower than -30 dB
Data Source
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Figure 3~4
AI summary
A multi-core amplification optical fiber includes a plurality of core portions doped with a rare-earth element, and a cladding portion positioned at an outer periphery of each of the core portions and having refractive index lower than refractive index of each of the core portions, in which when a concentration of the rare-earth element doped to each of the core portions is 250 ppm to 2000 ppm, a relative refractive index Δ of each of the core portions relative to the cladding portion is 0.5% to 2% at a wavelength of 1550 nm, and a core diameter of each of the core portions is 1 µm to 5 µm, a separation distance between each of the core portions and adjacent one of the core portions is set at equal to or larger than 30 µm and at equal to or smaller than 60 µm so that a crosstalk of light between the adjacent core portions is equal to or lower than -30 dB. Hereby a multi-core amplification optical fiber and a multi-core optical fiber amplifier capable of optical amplification while suppressing lowering of the qualtity in signal light are provided.