Optical Repeater SNR Deterioration in Mode-Division-Multiplexing Systems
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Solution Overview
Problem
Conventional optical repeaters in MDM optical transmission systems suffer from signal-to-noise ratio (SNR) deterioration due to mode demultiplexer losses, particularly in long-haul systems where differential mode delay and differential modal loss accumulate, affecting transmission quality.
Innovation Solution
The optical repeater design includes a mode demultiplexer, mode multiplexer, variable optical attenuators, and at least one multimode optical amplifier, with a multimode amplifier positioned on the input side of the mode demultiplexer to prevent SNR degradation, utilizing a cyclic mode permutation scheme and wavelength-equalizing filters to offset gain variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mode demultiplexer is used in the optical repeater, then the cyclic mode permutation scheme can be implemented to reduce DMD and DML accumulation, but the signal-to-noise ratio deteriorates due to demultiplexer losses
Solution Approach 1:
The patent applies preliminary action by placing the optical amplifier on the input side of the mode demultiplexer, before the signal enters the demultiplexer. This allows the signal to be amplified beforehand, compensating for the losses that will occur in the demultiplexer. The amplifier restores the signal power to a level sufficient to withstand the demultiplexer insertion loss, thereby maintaining the signal-to-noise ratio while still enabling the cyclic mode permutation scheme to function effectively for reducing DMD and DML accumulation.
2Length of stationary object
If transmission distance is increased to expand network coverage, then differential mode delay and differential modal loss accumulate, but transmission quality deteriorates
Solution Approach 1:
The patent implements periodic action through the cyclic mode permutation scheme, where the mode ordering is periodically swapped at each repeater station along the transmission line. This periodic reordering ensures that no single mode consistently experiences the worst propagation conditions over long distances. Combined with the input-side optical amplifier that periodically restores signal power at each repeater location, the system can maintain transmission quality over extended distances by counteracting the cumulative effects of DMD and DML through this periodic intervention strategy.
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 configuration effectively maintains a high signal-to-noise ratio by equalizing signal power among modes and compensating for span losses, ensuring reliable transmission quality across multiple spans.
Implementation Method 1
disposes one of the multimode optical amplifiers on an input side of the mode demultiplexer
Implementation Method 2
a mode demultiplexer connected to an incoming multimode optical fiber
Implementation Method 3
a mode multiplexer connected to a plurality of single-mode fibers that have passed through the variable optical attenuators, respectively
Data Source
AI summary
An optical repeater in a mode-division-multiplexing (MDM) optical transmission system prevents a signal-to-noise ratio (SNR) from deteriorating due to a loss of a mode demultiplexer. The optical repeater in the MDM optical transmission system is configured to include at least one multimode optical amplifier, a mode demultiplexer, a mode multiplexer, and variable optical attenuators. One of the multimode optical amplifiers is disposed on the input side of the mode demultiplexer.