Multicore Optical Fiber Layout for Low Cross-Talk and Connection Loss
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Solution Overview
Problem
Existing multi-core optical fibers face issues such as increased connection loss, unsuitability for high-density wavelength multiplexing transmission, and poor manufacturability due to the need for trench layers with large refractive index differences.
Innovation Solution
A multi-core optical fiber design with 12 or 16 core units, featuring a depressed layer and common cladding, arranged to minimize adjacent relationships and ensure line symmetry, with specific diameter and refractive index relationships to reduce cross-talk and leakage loss, allowing for standard coating diameters and improved manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trench layers with large refractive index differences are used, then cross-talk and leakage loss are reduced, but manufacturability deteriorates
Solution Approach 1:
The patent changes the refractive index parameter of the depressed layer to be smaller in absolute value (closer to zero) compared to conventional trench layers. Specifically, the relative refractive index difference Δdep is controlled to be smaller than conventional values, which reduces the difficulty of manufacturing while still achieving sufficient cross-talk and leakage loss reduction through optimized core arrangement and layer structure
Solution Approach 2:
The patent uses a composite structure combining a depressed layer with a common cladding, where the depressed layer has a refractive index lower than the common cladding. This composite structure replaces the need for traditional trench layers with large refractive index differences, achieving similar or better performance with improved manufacturability
2Reliability
If core center-to-center distance is increased, then cross-talk is reduced, but fiber diameter and density are affected
Solution Approach 1:
The patent optimizes the core center-to-center distance parameter to achieve a balance between cross-talk reduction and fiber density. By carefully controlling this distance along with the depressed layer refractive index, the patent achieves low cross-talk without requiring excessive spacing that would increase fiber diameter
Solution Approach 2:
The patent employs asymmetric core arrangement where cores are positioned to minimize adjacent relationships while maintaining line symmetry. This asymmetric optimization within symmetric constraints allows for reduced cross-talk while maintaining compact fiber diameter
3Ease of manufacture
If multiple core units are arranged in standard lattice patterns, then manufacturing is simplified, but connection loss increases
Solution Approach 1:
The patent introduces asymmetric core arrangement that breaks the conventional symmetric lattice pattern. Cores are positioned such that no adjacent relationship is established between cores having specific adjacent relationships, which reduces connection loss while maintaining manufacturability through line symmetry
Solution Approach 2:
The patent segments the core units into specific groups with controlled adjacent relationships. By dividing and arranging core units in this segmented manner, the patent reduces connection loss while keeping the overall structure simple enough for manufacturing
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 effectively reduces cross-talk and leakage loss, enabling bidirectional transmission suitable for long-distance communication in the C and L bands with reduced connection loss and improved manufacturability.
Implementation Method 1
a depressed layer covering an outer periphery of the core, the depressed layer having a refractive index lower than a maximum refractive index of the core
Implementation Method 2
a common cladding having a refractive index higher than the refractive index of the depressed layer and covering an outer periphery of each of the 12 or 16 core units
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3
AI summary
An MCF (100) according to the present disclosure comprises 12 or 16 core units each including a core (110) and a depressed layer (122), a common cladding (120), and a resin coating (130). On the cross section, the core units are disposed such that an adjacency relationship is not established between cores (110) each establishing an adjacency relationship with a specific core (110), and are disposed such that the centers of the core units are line-symmetric with respect to a symmetry axis (LA) that is an axis crossing a central axis (AX) and not passing the center of any of the core units. The outer diameter of the resin coating (130) is 250±15 µm, an effective cross-sectional area (Aeff_1550) at a wavelength of 1.550 µm is 70 µm2 or more, and the cut-off wavelength (λcc) of a cable with a length of 22 m is 1.530 µm or less. The center-to-center distance (A) of adjacent cores, the shortest distance (d_coat) from a core center to an interface between the common cladding and the resin coating (130), and the smallest outer diameter (CD) of the common cladding (120) satisfy a specific relationship.