Grating Coupler Assembly with Small Mode-Field Diameter Fiber
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Solution Overview
Problem
Conventional single-mode fibers with small mode-field diameters result in reduced coupling efficiency and larger grating coupler footprints in photonic-integrated-circuit systems, limiting the integration density of optical connections.
Innovation Solution
A grating-coupler assembly using optical fibers with a mode-field diameter of 5 μm to 6 μm, which achieves a coupling efficiency of 0.7 or greater, allowing for a reduced coupler footprint and increased integration density by optimizing the refractive index profile and using multi-core fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-mode fibers with small mode-field diameter are used, then the coupling efficiency is reduced, but the grating coupler footprint is increased
Solution Approach 1:
The patent changes the mode-field diameter parameter of the optical fiber from conventional values (typically 10 μm or larger) to a smaller range (5-6 μm). This parameter change enables both high coupling efficiency and reduced grating coupler footprint, as the smaller mode field diameter allows for better mode matching with the waveguide while requiring fewer grating periods for effective coupling.
2Productivity
If the mode-field diameter is reduced to increase integration density, then the coupling efficiency decreases, but the grating coupler area must be increased
Solution Approach 1:
The patent optimizes the mode-field diameter parameter to a specific range (5-6 μm) that simultaneously achieves high integration density and maintains coupling efficiency of 0.7 or greater. This optimized parameter enables smaller grating coupler footprints while preserving reliable optical coupling.
Solution Approach 2:
The patent employs an intervening medium with refractive index nm>1 between the optical fiber and grating coupler to locally enhance the coupling interaction. This localized refractive index modification improves the coupling efficiency for small mode-field diameter fibers without requiring larger grating areas, thereby maintaining high integration density.
3Reliability
If conventional single-mode fibers are used, then the coupling efficiency can be maintained, but the grating coupler footprint is larger reducing integration density
Solution Approach 1:
The patent changes the mode-field diameter parameter to 5-6 μm, which enables both high coupling efficiency (CE≧0.7) and reduced grating coupler footprint. This parameter optimization directly increases integration density by allowing smaller coupler areas while maintaining reliable optical coupling.
Solution Approach 2:
The patent introduces an intervening medium with refractive index nm>1 between the fiber and grating coupler, adding a dimensional element (refractive index layer) that enhances coupling efficiency for small mode-field fibers without increasing the lateral footprint, thereby enabling higher integration density.
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 high coupling efficiency and a significant reduction in grating coupler footprint, thereby increasing the integration density of optical connections in photonic-integrated-circuit systems.
Implementation Method 1
at least one grating coupler supported by the SOI substrate and optically coupled to the at least one silicon waveguide
Data Source
AI summary
A grating-coupler assembly with a small mode-field diameter for photonic-integrated-circuit systems is disclosed. The assembly includes a silicon waveguide supported by a silicon-on-insulator substrate, and a grating coupler supported by the substrate and optically coupled to the silicon waveguide. The assembly has an optical fiber with a mode-field diameter in the range from 5 μm to 6 μm. One end of the optical fiber is disposed adjacent the grating coupler to define a coupling efficiency of 0.7 or greater.