Multimode Fiber-to-Waveguide Coupling via Tapered Evanescent Transition
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Solution Overview
Problem
Efficient optical coupling between multimode fibers and waveguides is hindered by structural differences and alignment issues, leading to optical loss and variability in coupling efficiency.
Innovation Solution
The implementation of a multimode fiber-to-waveguide coupler using tapered terminals for evanescent coupling, where the multimode fiber and waveguide are spatially overlapped to achieve adiabatic transition and near-lossless mode coupling, allowing for selective handling and processing of spatial modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional fiber-to-waveguide coupling is used, then the coupling structure is simple, but optical loss is high and coupling efficiency varies with alignment
Solution Approach 1:
The patent employs dynamic tapering of both the fiber terminal and waveguide terminal, where the cross-sectional dimensions vary continuously along the coupling length. This dynamic geometric transformation enables adiabatic mode coupling, allowing the optical modes to adapt gradually from fiber to waveguide, thereby minimizing optical loss while maintaining a relatively simple overall structure.
Solution Approach 2:
The invention changes the geometric parameters (cross-sectional dimensions) of both the fiber and waveguide terminals along the coupling direction. By gradually transforming the dimensions from the fiber's larger cross-section to the waveguide's smaller cross-section, the patent achieves efficient mode matching and reduces optical loss without requiring complex alignment mechanisms.
2Ease of operation
If alignment between fiber and waveguide is relaxed, then ease of operation improves, but coupling efficiency varies
Solution Approach 1:
The dynamic tapering structure creates a gradual transition zone where the optical field adapts continuously from the fiber mode to the waveguide mode. This dynamic transformation process is less sensitive to misalignment because the overlapping region extends along the coupling direction, providing a larger effective coupling area that tolerates positional variations while maintaining stable coupling efficiency.
Solution Approach 2:
The patent extends the coupling interaction from a point-like interface to a distributed interaction along the coupling direction (adding a spatial dimension). This dimensional extension creates an extended overlap region between the tapered fiber and waveguide, which increases alignment tolerance while maintaining coupling efficiency through the extended interaction length.
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 approach enables efficient coupling of light between multimode fibers and waveguides, achieving high power transfer (e.g., 50% in simulations) and facilitating advanced signal processing and data transmission by converting fiber modes to waveguide modes for on-chip processing.
Implementation Method 1
the optical fiber located above the optical waveguide and optically coupled to the optical waveguide via evanescent coupling to allow light to be coupled between the optical fiber and the optical waveguide
Implementation Method 2
the tapered fiber terminal and the tapered waveguide terminal spatially overlap with each other to cause adiabatic transition of guided light and to cause coupling of different modes between the tapered fiber terminal and the tapered waveguide terminal
Data Source
AI summary
Optical coupling designs are disclosed to provide a photonic device, for example, that includes a substrate; an optical waveguide formed on the substrate and configured as a multimode waveguide to support light in different optical waveguide modes; and an optical fiber structured as a multimode fiber to support light in different optical fiber modes, the optical fiber located above the optical waveguide and optically coupled to the optical waveguide via evanescent coupling to allow light to be coupled between the optical fiber and the optical waveguide.