Optical Fiber Mode Coupling Control for MIMO Complexity
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Solution Overview
Problem
In optical fiber communication systems, large Differential Mode Delay (DMD) complicates MIMO processing due to mode coupling, and reducing effective refractive index differences between LP modes can lead to loss of signal or noise interference, affecting the propagation of light beams.
Innovation Solution
An optical fiber design that includes a signal light propagation core allowing propagation of up to (x+1)-th order LP modes, with a coupled member that suppresses coupling with x-th order LP modes, enabling mode coupling only between x-th and (x+1)-th order LP modes, and using a clad or side core as a coupled member to manage refractive index differences and confine communication modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If mode coupling is caused by reducing effective refractive index differences between LP modes, then the load of MIMO processing is reduced, but light beam loss and noise interference occur
Solution Approach 1:
The patent segments the LP modes into two groups: communication modes (LP01, LP11, LP21) that are allowed to mode couple, and non-communication modes (LP02, LP12, LP31, etc.) that are suppressed from coupling. This is achieved by designing the clad refractive index profile to create specific effective refractive index differences between mode groups, thereby reducing MIMO processing complexity for communication modes while preventing noise from non-communication modes
Solution Approach 2:
The patent applies local quality by creating different refractive index characteristics for different radial regions of the clad. The clad has a first region with refractive index n2 and a second region with refractive index n3, where n1 < n2 < n3. This localized refractive index variation enables selective mode coupling: communication modes experience coupling that reduces DMD, while non-communication modes are suppressed from coupling, thus maintaining signal reliability
2Device complexity
If effective refractive index differences are reduced to enable mode coupling, then DMD is reduced, but difference between highest order LP mode effective refractive index and clad refractive index becomes small causing light beam loss
Solution Approach 1:
The patent changes the refractive index parameters of the clad structure, introducing a two-region clad with refractive indices n2 and n3 (where n1 < n2 < n3). This parameter change creates optimal effective refractive index differences that enable mode coupling for communication modes while maintaining sufficient index difference between the highest order communication mode and the clad to prevent light beam loss
3Device complexity
If effective refractive index differences are reduced to enable mode coupling, then DMD is reduced, but unnecessary LP modes propagate causing noise and mode coupling with necessary light beams
Solution Approach 1:
The patent segments modes into communication modes and non-communication modes with different coupling characteristics. The clad refractive index profile is designed so that communication modes (LP01, LP11, LP21) have small effective refractive index differences enabling coupling, while non-communication modes (LP02, LP12, LP31) have large differences suppressing coupling, thereby eliminating noise generation from unnecessary modes
Solution Approach 2:
The patent applies local quality by creating different refractive index characteristics for different radial regions of the clad. The clad has a first region with refractive index n2 and a second region with refractive index n3, where n1 < n2 < n3. This localized refractive index variation enables selective mode coupling: communication modes experience coupling that reduces DMD, while non-communication modes are suppressed from coupling, thus maintaining signal reliability
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 design ensures appropriate propagation of multiple LP modes while minimizing interference from non-communication modes, enhancing signal confinement and reducing noise influence, thus simplifying MIMO processing and improving communication efficiency.
Implementation Method 1
when mode coupling occurs, the Differential Mode Delays are averaged to reduce the load of the MIMO processing
Implementation Method 2
An optical fiber that communicates using light beams of up to x-th order LP mode
Data Source
AI summary
An optical fiber that communicates in a predetermined communication band includes: a signal light propagation core that propagates light beams of up to (x+1)-th order LP mode, where x is an integer of two or more; and a coupler that propagates a light beam that is: coupled with a light beam of the (x+1)-th order LP mode propagating through the signal light propagation core, and suppressed from being coupled with light beams of up to the x-th order LP mode propagating through the signal light propagation core, wherein, mode coupling of the light beams of up to the x-th order LP mode propagating through the signal light propagation core is performed, and mode coupling between the light beam of the x-th order LP mode and the light beam of (x+1)-th order LP mode is suppressed.