Step-Index Multimode Fiber Spin Profile for Mode Coupling Reduction
Solution Overview
Problem
Conventional mode division multiplexing systems face challenges with mode coupling, leading to inter-modal interference and power loss in optical fibers, particularly in few-mode fibers and multimode fibers, which complicates signal transmission and demultiplexing due to temporal delays between spatial modes.
Innovation Solution
A step-index multimode fiber with a spin profile varying along its length, using either an Amplitude Modulation, Frequency Modulation, or sinusoidal spin function, is employed to minimize temporal spacing between spatial modes, allowing for simultaneous demultiplexing and reducing inter-modal coupling interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional few-mode fibers with round core are used for mode division multiplexing, then spatial modes can be supported in two-dimensional distribution, but mode coupling among guided modes causes inter-modal coupling interference and power loss
Solution Approach 1:
The patent transforms the conventional round core symmetric structure into an elliptical core asymmetric structure. This asymmetry fundamentally changes the mode distribution from two-dimensional (radial and azimuthal) to primarily radial distribution, reducing mode coupling and inter-modal interference while maintaining support for multiple spatial modes.
Solution Approach 2:
The patent introduces a spin profile that varies along the fiber length, creating local variations in the refractive index distribution. This local quality change enables dynamic control of mode propagation characteristics, reducing modal dispersion and improving signal transmission quality while maintaining high mode capacity.
2Quantity of substance
If multimode fiber is used for mode division multiplexing, then modal groups can be transmitted, but spatial modes are subject to channel crosstalk due to mode coupling effects especially when subjected to bending or twisting
Solution Approach 1:
The elliptical core structure creates asymmetric mode confinement that reduces sensitivity to external perturbations such as bending and twisting. The mode fields are more tightly confined in the radial direction, reducing overlap and coupling between modes even under mechanical stress.
Solution Approach 2:
The spin profile is pre-engineered into the fiber structure during manufacturing, creating a predetermined pattern of refractive index variations along the fiber length. This preliminary structural modification proactively compensates for mode coupling effects before they can cause channel crosstalk during transmission.
3Reliability
If MIMO processing is used to handle mode coupling, then channel crosstalk can be mitigated, but the complexity of maintaining coherent transmission of multiple modal groups increases
Solution Approach 1:
The patent extracts and addresses the root cause of mode coupling by modifying the fiber structure itself (elliptical core with spin profile), rather than relying entirely on complex MIMO signal processing. This structural solution reduces the burden on digital signal processing systems.
Solution Approach 2:
The patent changes the fundamental structural parameters of the fiber (core shape from round to elliptical, introduction of spin profile) to alter mode propagation characteristics. This physical parameter modification reduces mode coupling at the source, simplifying subsequent signal processing requirements.
4Quantity of substance
If parabolic refractive index profile MMF is used for mode division multiplexing, then different LP modes can be utilized, but large time delay differences between modes make it difficult to demultiplex optical signals in time domain
Solution Approach 1:
The elliptical core structure creates asymmetric mode confinement that equalizes propagation velocities of different spatial modes more effectively than parabolic profiles. The radial-only mode distribution in elliptical fibers reduces differential mode delay compared to the two-dimensional mode distribution in circular fibers with parabolic profiles.
Solution Approach 2:
The patent changes the refractive index profile from a parabolic gradient to a step-index profile combined with a spin variation. This parameter change fundamentally alters the dispersion characteristics, reducing time delay differences between modes and enabling more effective time-domain demultiplexing.
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 mode division multiplexing with reduced temporal delays between spatial modes, enhancing bandwidth capacity and facilitating dense MIMO DSP by minimizing processing windows and inter-modal interference.
Implementation Method 1
at least one core with a central axis, a first relative refractive index Δ1, a radius r, and a diameter d extending through the central axis; at least one cladding layer surrounding the core, the at least one cladding layer comprising a second relative refractive index Δ2 smaller than the first relative refractive index Δ1 of the at least one core
Data Source
AI summary
Mode Division Multiplexing (MDM) systems using step-index multimode fibers (MMF) are disclosed herein, where the step-index MMF includes at least one glass core and at least one cladding surrounding the core, wherein the step-index MMF comprises a spin profile that was imparted into the step-index MMF during draw by a spinning apparatus according to a spin function, wherein the spin function comprises at least one of sinusoidal function, a Amplitude Modulation (AM) function, a Frequency Modulation (FM) function, or a combination thereof.