Solid-to-Hollow-Core Ferrule Coupling With Mode-Field Transition
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Solution Overview
Problem
Challenges exist in providing low-loss and inexpensive interfaces between solid-core and hollow-core optical fibers due to core size and mode field diameter mismatches, leading to significant insertion and back reflection losses.
Innovation Solution
A fiber optic coupling assembly with fiber optic ferrules having non-perpendicular and non-parallel end faces and bores, incorporating a mode field diameter transition region to bridge the mismatch, and optionally using antireflection coatings to reduce reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If simple butt coupling is used between solid core and hollow core optical fibers, then the interface is easy to manufacture, but significant insertion losses and back reflection losses occur
Solution Approach 1:
The patent introduces an intermediary mode field diameter transition region between the solid core optical fiber and hollow core optical fiber. This transition region acts as a mediator that gradually bridges the mode field diameter mismatch, reducing Fresnel reflection losses and insertion losses while maintaining ease of manufacture through a relatively simple ferrule structure.
Solution Approach 2:
The patent applies parameter changes by varying the mode field diameter through the transition region. The mode field diameter gradually changes from the smaller diameter of the solid core fiber to the larger diameter of the hollow core fiber, optimizing the coupling interface and reducing energy losses.
2Device complexity
If conventional ferrules with perpendicular end faces are used, then the structure is simple, but significant Fresnel reflection losses occur at the interface
Solution Approach 1:
The patent employs asymmetry by using non-perpendicular end faces (angled at approximately 8 degrees) in the ferrule structure. This asymmetric angular configuration reduces Fresnel reflection losses by optimizing the refraction conditions at the interface between solid core and hollow core fibers, while maintaining relatively simple device complexity.
3Loss of energy
If mode field diameter transition region is added to bridge mismatch, then coupling loss is reduced, but device complexity increases
Solution Approach 1:
The patent merges the mode field diameter transition region with the existing ferrule structure rather than adding it as a separate component. The transition region is integrated into the ferrule body, allowing the ferrule to simultaneously provide mechanical support, alignment, and mode field diameter transition functionality, thereby reducing overall device complexity.
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 enables low-loss and efficient coupling between solid-core and hollow-core optical fibers, reducing insertion losses and back reflections to below -65 dB, facilitating high-speed signal transmission.
Implementation Method 1
a mode field diameter transition region that provides a transition between mode field diameter values of the solid core optical fiber that are different at the first proximal and first distal end faces
Implementation Method 2
these different types of optical fibers also include central portions with different refractive index values, and significant Fresnel reflection losses would also result
Implementation Method 3
a beam refracted at the first end face, corresponding to an interface between a solid core optical fiber and a hollow core optical fiber
Data Source
AI summary
A fiber coupling assembly for interfacing solid core and a hollow core optical fibers includes first and second fiber optic ferrules each having a bore between proximal and distal end faces thereof. At least one ferrule end face is non-perpendicular to longitudinal axes of the ferrules. A bore of one ferrule contains a hollow core optical fiber, and a bore of the other optic ferrule contains a solid core optical fiber with a mode field diameter (MFD) transition region, to bridge a MFD mismatch between the fibers. An air gap may be provided between at least portions of ferrules at an inter-ferrule region. A fiber optic ferrule includes a bore that is non-parallel with a longitudinal axis of the ferrule, and at least one end face that is non-perpendicular to the longitudinal axis, with an optical fiber in the bore optionally including a MFD transition region.