Fiber Optic Ferrule Interface for Low-Loss Hollow-Core Coupling
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Solution Overview
Problem
The challenge of providing low-loss and inexpensive interfaces between solid-core and hollow-core optical fibers is hindered by core size and mode field diameter mismatches, as well as significant Fresnel reflection losses in conventional mechanical connectors.
Innovation Solution
A fiber optic coupling assembly is designed 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 reflection losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple butt coupling between solid core and hollow core optical fibers is used, then the device complexity is reduced, but significant insertion losses and back reflection losses occur
Solution Approach 1:
The patent introduces an intermediary mode field diameter transition region that acts as a mediator between the solid core optical fiber and hollow core optical fiber. This transition region gradually transforms the mode field diameter from the solid core fiber to match the hollow core fiber, reducing abrupt mismatches and minimizing insertion losses and back reflections while maintaining relatively simple coupling interface design
Solution Approach 2:
The patent applies parameter changes by gradually transforming the mode field diameter parameter along the transition region. The mode field diameter transitions from the solid core fiber's diameter to the hollow core fiber's diameter through a controlled gradient, enabling smooth impedance matching and reducing reflection losses without requiring complex coupling mechanisms
2Ease of manufacture
If conventional mechanical connectors with perpendicular end faces are used, then the ease of manufacture is improved, but significant Fresnel reflection losses occur
Solution Approach 1:
The patent introduces asymmetry by tilting the end faces of the ferrules away from the perpendicular orientation. This asymmetric angular configuration reduces Fresnel reflections at the air-glass interfaces by changing the reflection geometry, while the tilt angle is optimized to balance manufacturing complexity with reflection reduction performance
Solution Approach 2:
The patent employs counteracting measures by using antireflection coatings on the tilted end faces to further compensate for residual reflections. The combination of angular tilting and coating creates a multi-layered approach that counterweights the inherent Fresnel reflections that occur at dielectric interfaces
3Loss of energy
If core size and mode field diameter mismatch between solid core and hollow core optical fibers is addressed, then the loss of energy is reduced, but the device complexity increases
Solution Approach 1:
The patent applies local quality by creating a transition region with locally varying properties between the solid core and hollow core fibers. The mode field diameter transition region has gradually changing characteristics that are tailored to match the specific core sizes and mode field diameters of the connected fibers, reducing propagation losses without requiring complex overall interface design
Solution Approach 2:
The patent addresses the mode field diameter mismatch by introducing a transitional dimension in the form of a gradient transition region. This dimensional approach allows the mode field to evolve continuously from one fiber type to another, effectively bridging the size mismatch while maintaining a relatively simple connector structure
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, low-reflection coupling between solid-core and hollow-core optical fibers, supporting high-speed signal transmission with reduced insertion and back reflection losses.
Implementation Method 1
a beam refracted at the first end face, corresponding to an interface between a solid core optical fiber and a hollow core optical fiber, to be propagated through an optical fiber
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 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
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.