Multi-core optical fiber with depressed cladding to suppress cross-talk
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Solution Overview
Problem
Current multi-core optical fibers face challenges in densely packing core portions while effectively suppressing cross-talk between them, which limits their capacity and efficiency in optical communication systems.
Innovation Solution
A multi-core optical fiber design featuring a center core portion, a second core portion, and a depressed portion, each with specific refractive indices, arranged to minimize cross-talk, along with a manufacturing method using capillaries to form the optical fiber preform and draw the fiber, ensuring an interval distance that maintains cross-talk below -30 dB over a total length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If core portions are densely packed to increase capacity, then the number of cores per fiber increases, but cross-talk between adjacent core portions increases
Solution Approach 1:
A depressed portion with refractive index lower than both the second core portion and the cladding portion is introduced as an intermediary structure between adjacent core portions. This depressed portion acts as a refractive index barrier that suppresses optical field overlap and reduces cross-talk between densely packed core portions, enabling high-capacity transmission with controlled interference.
Solution Approach 2:
The optical fiber employs a heterogeneous refractive index structure where different regions (center core portion, second core portion, depressed portion, and cladding portion) have distinctly different refractive indices. This local quality variation creates effective optical isolation between adjacent cores while maintaining single-mode operation, allowing dense packing without excessive cross-talk.
2Area of moving object
If a trench-assisted refractive index profile is used to increase effective core area, then the effective core area increases, but the structure complexity increases
Solution Approach 1:
The core structure is segmented into multiple functional regions: a center core portion, a surrounding second core portion, and an outer depressed portion. This segmentation allows each region to serve a specific optical function while collectively achieving a large effective core area with controlled mode confinement through the trench-assisted refractive index profile.
Solution Approach 2:
The optical fiber structure employs a nested configuration where the center core portion is surrounded by the second core portion, which is in turn surrounded by the depressed portion, forming concentric rings. This nested structure efficiently utilizes the available cross-sectional area to maximize the effective core area while maintaining a compact overall geometry.
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 allows for more densely packed core portions with reduced cross-talk, enhancing the effective core area and bending loss performance, thereby improving the capacity and efficiency of optical communication systems.
Implementation Method 1
each of the core portions includes a center core portion that is positioned at a center of each core portion and that has a refractive index which is greater than that of the cladding portion, a second core portion that is formed so as to surround an outside of the center core portion and that has a refractive index which is less than that of the center core portion, and a depressed portion that is formed so as to surround an outside of the second core portion and that has a refractive index which is less than those of the second core portion and the cladding portion
Data Source
AI summary
A multi-core optical fiber includes: a plurality of core portions; and a cladding portion positioned so as to surround each of the core portions, wherein each core portion includes a center core portion that has a refractive index greater than that of the cladding portion, a second core portion that is formed so as to surround the center core portion and that has a refractive index less than that of the center core portion, and a depressed portion that is formed so as to surround the second core portion and that has a refractive index less than those of the second core portion and the cladding portion, and an interval distance between the adjacent core portions is set such that optical cross-talk between the core portions for a total length of the multi-core optical fiber is equal to or less than −30 dB at a wavelength of 1.55 μm.