Tapered Fiber Bundle Coupler for Low-Loss Multicore Alignment
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Solution Overview
Problem
The challenge lies in achieving low-loss coupling between standard single-core, single-mode fibers and multicore amplifier fibers, particularly in maintaining constant gain across varying input power conditions, due to differences in geometry and mode field diameters, which existing solutions like tapered fiber bundles fail to address effectively.
Innovation Solution
A tapered fiber bundle coupler with specially designed pedestal fibers, configured to maintain matching mode field diameters and reduce crosstalk, is used to provide a low-loss interface between input fibers and multicore gain fibers, employing unique refractive index profiles and tapering ratios to align core and mode field diameters with the multicore fiber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If standard single-core fibers are coupled to multicore amplifier fibers using conventional methods, then the coupling process is simple, but the loss is high due to geometry and mode field diameter mismatches
Solution Approach 1:
The patent introduces a tapered fiber bundle as an intermediary component between standard single-core input fibers and multicore amplifier fibers. This tapered fiber bundle acts as a transition structure that gradually transforms the mode field diameter and geometric configuration, enabling low-loss coupling by providing a gradual transition rather than an abrupt interface between mismatched fiber types.
Solution Approach 2:
The patent employs parameter changes by varying the taper ratio and pedestal fiber dimensions to optimize the transition. Specifically, the tapered fiber bundle uses controlled changes in diameter along its length, with different pedestal fiber parameters (core diameter, cladding diameter, numerical aperture) selected to match both the input single-core fibers and the output multicore amplifier fibers, thereby minimizing coupling loss.
2Shape
If tapered fiber bundles are used to achieve geometry matching, then the core pitch alignment is improved, but the mode field diameter increases causing higher loss
Solution Approach 1:
The patent applies local quality by using different pedestal fiber types with specific properties in different regions of the tapered bundle. Each pedestal fiber is selected with particular core diameter, cladding diameter, and numerical aperture values optimized for its specific position and function within the bundle, allowing simultaneous achievement of core pitch alignment and mode field diameter control.
Solution Approach 2:
The patent uses composite structures by combining multiple pedestal fibers with different refractive index profiles and dimensional characteristics into a single tapered bundle. This composite approach allows the bundle to simultaneously provide geometric transformation for core pitch alignment while maintaining appropriate mode field diameters through the careful selection and arrangement of individual pedestal fiber properties.
3Productivity
If multiple input fibers are coupled to individual multicore fiber cores, then the network capacity is expanded, but the crosstalk between cores increases
Solution Approach 1:
The patent applies segmentation by dividing the coupling process into individual fiber-to-core transitions within the tapered bundle. Each pedestal fiber in the bundle independently couples light from a specific input fiber to a corresponding multicore fiber core, creating spatially separated transmission paths that minimize interference and crosstalk between adjacent cores while maintaining high network capacity.
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 solution enables efficient low-loss coupling with reduced crosstalk, allowing for consistent amplification across all cores, achieving acceptable loss and crosstalk levels, thereby maintaining constant gain independent of input power fluctuations.
Implementation Method 1
A coupler is constructed using a bundle of at least three dissimilar pedestal fibers, each fiber having a different numerical aperture, untapered mode field diameter, and tapered mode field diameter
Data Source
Figure 1A~1B
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AI summary
An optical pedestal fiber is configured to be taperable to form a tapered fiber having a mode field diameter at the tapered end that differs from the mode field diameter at the untapered end in correspondence with the difference between the cladding diameter at the tapered end and the cladding diameter at the untapered end. A plurality of such pedestal fibers can be used to construct a tapered fiber bundle coupler that provides matching of both core pitch and mode field diameter between a plurality of input fibers and individual cores of a multicore fiber. Further, the tapered fiber bundle coupler can be constructed using a plurality of fibers, in which individual fibers are configured to have different effective refractive indices, thereby suppressing crosstalk therebetween.