Modefield-Matched Coupling to Multicore Fiber
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Solution Overview
Problem
Current methods for coupling single-core fibers to multicore fibers result in excessive coupling losses and crosstalk due to surface tension effects during tapering, which are not suitable for multicore fibers with a large number of cores, as they alter the core and modefield shape, compromising signal transport efficiency.
Innovation Solution
A multi-hole fiber coupler and modefield-maintaining single-core fiber design that maintains precise core alignment and modefield diameter, using a pre-tapered multi-hole fiber coupler with holes configured to match the multicore fiber geometry, and a specially designed single-core fiber with a modified step-index profile to minimize crosstalk and maintain modefield properties over a large taper ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional tapering techniques are used to reduce outer diameter, then core alignment is achieved, but surface tension effects deform the outer surface and alter core shape, resulting in excessive coupling losses and crosstalk
Solution Approach 1:
The invention divides the fiber structure into multiple independent cores within a common cladding, allowing each core to be treated separately during coupling while maintaining precise geometric relationships. This segmentation enables modefield matching without the surface tension deformations that affect conventional single-core tapering.
Solution Approach 2:
The invention changes the refractive index parameters by introducing a depressed index region in the cladding surrounding each core. This parameter modification maintains modefield diameter during tapering and reduces sensitivity to alignment errors, thereby reducing coupling losses while preserving core shape integrity.
2Manufacturing precision
If tapering ratio is increased to match core spacing, then coupling alignment improves, but modefield diameter increases due to tapering, resulting in increased coupling losses
Solution Approach 1:
The depressed index cladding region modifies the modefield parameters to maintain a relatively constant modefield diameter even during significant tapering. This parameter change allows aggressive tapering for core spacing alignment without the usual penalty of modefield expansion and associated coupling losses.
Solution Approach 2:
The depressed index region acts as an intermediary structure between the core and the external environment, mediating the effect of tapering on the modefield. It provides a transition zone that maintains modefield properties during the coupling process.
3Volume of moving object
If outer diameter is reduced to match MCF dimensions, then cable density improves, but mechanical approaches like grinding increase complexity and chemical approaches like etching increase process complexity
Solution Approach 1:
The invention uses refractive index parameter changes in the cladding region to achieve the desired coupling properties without mechanical or chemical reduction processes. This approach maintains the outer diameter while achieving modefield matching through optical parameter modification rather than physical alteration.
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
Achieves low-loss modefield-matching coupling with minimal crosstalk, ensuring efficient signal transmission by maintaining modefield diameter and alignment, reducing coupling losses and crosstalk, and facilitating the use of multicore fibers with multiple cores.
Implementation Method 1
a multi-hole fiber coupler and modefield-maintaining single-core fiber design that maintains precise core alignment and modefield diameter
Implementation Method 2
surface tension during bundle tapering tends to smooth out the outer surface of the bundle into an approximately circular shape. Therefore, while the modefield diameters of the tapered cores may match the modefield diameters of the corresponding MCF cores, the surface tension effects introduce significant deformations into the outer cores in the bundle
Data Source
Figure 1A~1B
Figure 2
Figure 3~4
AI summary
Devices and techniques are described for connecting each of plurality of terminal to respective individual cores of a multicore fiber. Each of the plurality of terminals is provided with a respective length of a single-core fiber. The single-core fibers are configured to maintain modal properties that are substantially the same, within a tolerance range, at the front and rear ends, as the single-core fiber is tapered. The single-core fibers are assembled together. The front end of the assembly is tapered to form a front cross-section in which the single-core fiber cores are arranged in a configuration matching that of the cores of the multicore fiber.