Graded-Index Waveguide Optical Coupler for Modal Noise Reduction
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Solution Overview
Problem
Modal noise in multi-mode fiber systems causes signal distortion due to misalignment and environmental variations, limiting the performance of Radio over Fiber systems and other high-speed data transmission networks.
Innovation Solution
An optical coupler with a graded-index waveguide is used to match the mode profiles of different optical fibers, eliminating energy coupling between modes with different indices, thereby reducing modal noise through a refractive index profile designed for optimal coupling efficiency and low transmission loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-mode fibers are used for data transmission in LANs and RoF systems, then data transmission capability and system simplicity are improved, but modal noise causes signal distortion due to misalignment and environmental variations
Solution Approach 1:
The patent introduces a mode field adapter as an intermediary component between two multi-mode fibers with different mode field diameters. This adapter gradually transforms the mode field distribution, enabling efficient coupling between fibers of different sizes while minimizing modal noise and signal distortion, thus maintaining both high productivity and reliability
Solution Approach 2:
The patent employs gradual parameter changes in the mode field adapter by varying the refractive index profile along the propagation direction. This continuous transformation of the mode field diameter parameter allows smooth adaptation between different fiber types, reducing abrupt mode coupling that causes modal noise while preserving data transmission capability
2Reliability
If misalignment between fiber connections is minimized to reduce modal noise, then signal quality is improved, but alignment precision requirements and manufacturing complexity increase
Solution Approach 1:
The mode field adapter performs preliminary mode field transformation before the light reaches the connection point between fibers. By pre-adapting the mode field distribution to match the receiving fiber's characteristics, the system becomes much less sensitive to misalignment errors, reducing the required manufacturing precision while maintaining signal quality
Solution Approach 2:
The adapter provides a cushioning effect against misalignment by gradually transforming modes over an extended length. This gradual transition acts as a buffer that compensates for potential misalignments, reducing the impact of positioning errors on signal quality without requiring extremely tight manufacturing tolerances
3Stability of the object's composition
If environmental temperature and mechanical stress variations are controlled to reduce modal noise, then signal stability is improved, but system complexity and control requirements increase
Solution Approach 1:
The mode field adapter provides self-service stabilization by its inherent gradual mode transformation structure. The extended adaptation length naturally averages out the effects of temperature and stress variations, providing passive stability without requiring active sensing or control systems, thus improving signal stability while avoiding increased device complexity
4Ease of manufacture
If graded-index waveguide with optimized refractive index profile is used, then mode coupling efficiency is improved, but manufacturing precision and design complexity increase
Solution Approach 1:
The patent implements local quality variations in the mode field adapter by creating a refractive index profile that changes along the propagation direction. Different sections of the adapter have different index characteristics optimized for their specific transformation task, achieving high coupling efficiency through localized optimization rather than requiring uniform high precision throughout
Solution Approach 2:
The patent uses a longer adapter length than the theoretical minimum required for mode transformation. This excessive action provides a margin that tolerates variations in refractive index profile manufacturing, allowing achieved coupling efficiency close to optimal even with moderate manufacturing precision
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 achieves significant reduction in modal noise, leading to higher data security, lower bit error rates, and increased data transmission rates without the need for additional electronic systems, enabling perfect alignment and reduced costs for connectors and alignment processes.
Implementation Method 1
an optical coupler connectable between a first optical waveguide and a second optical waveguide for coupling modulated light guided by the first optical waveguide into multiple modes of the second optical waveguide
Implementation Method 2
a graded-index waveguide comprising a core material orientated with respect to an optical axis of the optical coupler, the core material having a refractive index decreasing with increasing distance from the optical axis
Data Source
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AI summary
The invention relates to an optical coupler (200) connectable between a first optical waveguide (201) and a second optical waveguide (203) for coupling modulated light guided by the first optical waveguide (201) into multiple modes of the second optical waveguide (203), the optical coupler comprising: a graded-index waveguide comprising a core material orientated with respect to an optical axis of the optical coupler, the core material having a refractive index decreasing with increasing distance from the optical axis of the optical coupler, wherein a refractive index profile of the core material is designed in accordance to an optimality criterion with respect to conversion of the modulated light of the first waveguide into the multiple modes of the second waveguide, such that an energy coupling between modes of the first optical waveguide and the second optical waveguide which modes have different indices is eliminated.