Optical Fiber Transmission System MIMO Crosstalk Reduction
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Solution Overview
Problem
Existing MIMO-based optical fiber transmission systems face challenges in reducing inter-mode crosstalk while minimizing the increase in processing load, particularly at fiber connection points where axial offset occurs, leading to increased crosstalk levels.
Innovation Solution
The system employs a MIMO configuration that limits input to specific spatial mode groups with higher propagation constants, using input-end and intermediate crosstalk reducing means to restrict the propagation of certain modes, such as the LP11 mode, and features a refractive index profile with a trench layer to manage light intensity, allowing only (M - 1) spatial mode groups for transmission, where M is greater than or equal to three.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MIMO configuration involving collective input and output of all spatial modes is adopted, then inter-mode crosstalk compensation is improved, but processing load increases significantly
Solution Approach 1:
The patent segments the MIMO processing into separate MIMO configurations for each spatial mode group (LP01, LP11, LP21, LP02) rather than collective processing of all modes. This segmentation reduces the processing load while maintaining effective crosstalk compensation within each mode group, resolving the contradiction between reliability and device complexity.
2Ease of operation
If fiber connection is performed with axial offset, then ease of operation is improved, but inter-mode crosstalk increases
Solution Approach 1:
The patent introduces a mode coupling section before the measurement section that intentionally induces mode coupling to compensate for the crosstalk generated by axial offset in fiber connections. This beforehand cushioning approach allows fiber connections to be performed with realistic axial offsets while maintaining low crosstalk levels through the compensating mode coupling effect.
3Productivity
If all spatial mode groups are used for signal transmission, then productivity is improved, but inter-mode crosstalk increases due to mode coupling
Solution Approach 1:
The patent introduces a mode coupling section as an intermediary component between the input and measurement sections. This intermediary induces controlled mode coupling that compensates for the crosstalk generated when multiple spatial mode groups are used for transmission, allowing high productivity while maintaining low crosstalk levels through the mediating coupling effect.
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 effectively reduces inter-mode crosstalk while maintaining a manageable processing load, achieving crosstalk levels of -50 dB or less with realistic axial offsets, enabling long-distance mode division multiplexed transmission with reduced dependency on axial offset precision.
Implementation Method 1
an optical fiber which allows M degenerate spatial mode groups to propagate in at least one core or core group with one cladding
Implementation Method 2
features a refractive index profile with a trench layer to manage light intensity
Data Source
Figure 1~3
Figure 4(a)~4(e)
Figure 5~6
AI summary
An object is to provide an optical fiber transmission system that has a structure for effectively reducing inter-mode XT while reducing an increase in processing load in a MIMO configuration. For a transmission line that allows propagation of at least three degenerate spatial mode groups in at least one core or core group, an embodiment of crosstalk reducing means limits input of an optical signal to at least one of spatial mode groups having a transmission loss of 1 dB/km or less, except a spatial mode group having the smallest propagation constant.