Per-Span Nonlinear Interference Characterization via VOA Dithering
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Solution Overview
Problem
Existing methods for quantifying nonlinear interference (NLI) in fiber optic communication systems are challenging due to unknown or mis-provisioned fiber properties, and existing power control approaches suffer from errors in modeling and measurement, leading to suboptimal launch power settings that affect noise-to-signal ratio (NSR) and channel capacity.
Innovation Solution
The implementation of a system using variable optical attenuators (VOAs) before and after each span in an optical link to isolate and measure NLI on a per-span basis, allowing for accurate estimation of noise performance and optimization of launch power settings through phase-sensitive detection and dithering techniques, while maintaining minimal impact on existing traffic channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing power control approaches based on modeling are used, then launch power can be controlled, but measurement errors and modeling errors lead to suboptimal performance
Solution Approach 1:
The patent divides the optical link into individual spans and uses VOAs to isolate each span for separate NLI measurement. This segmentation allows per-span characterization without interference from other spans, resolving the measurement accuracy issue by enabling independent measurement of each span's nonlinear interference contribution.
Solution Approach 2:
The patent introduces variable optical attenuators (VOAs) as intermediary devices to control and isolate the optical signal in each span. These VOAs enable precise control of launch power into individual spans and allow the measurement system to separate NLI contributions from different spans, thereby improving both measurement precision and system reliability.
2Reliability
If per-span NLI measurement is implemented, then noise performance can be optimized, but system complexity increases due to additional components
Solution Approach 1:
The patent makes the VOAs multi-functional by using them for both NLI measurement and launch power control. The same VOA components that enable per-span isolation for measurement also serve as the control mechanism for optimizing launch power, thereby improving noise performance without proportionally increasing system complexity.
Solution Approach 2:
The measurement system uses the existing VOA infrastructure in the optical link to perform both measurement and control functions. The VOAs that are already present for power management are utilized for NLI characterization, allowing the system to self-characterize without requiring entirely separate measurement equipment.
3Measurement precision
If commissioning-time fiber characterization is performed, then fiber parameters can be measured, but the system cannot be optimized once in-service
Solution Approach 1:
The patent enables continuous NLI measurement and optimization capability throughout the system's operational life. By using VOAs to isolate and measure per-span NLI in-service, the system can continuously characterize fiber parameters and adjust launch power to optimize performance, rather than being limited to one-time commissioning measurements.
Solution Approach 2:
The patent transforms the static, one-time fiber characterization performed at commissioning into a dynamic, ongoing measurement process. The in-service measurement capability allows the system to adapt to changing conditions over time, updating fiber parameter knowledge and optimizing performance continuously rather than relying on fixed initial characterizations.
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 accurate in-service characterization of NLI and optimization of launch power, improving noise performance and channel capacity by isolating NLI contributions from each span, thereby enhancing the overall efficiency and reliability of optical communication systems.
Implementation Method 1
having a pair of variable optical attenuators (VOAs) before and optionally after the line fiber of each span, where the first VOA before the fiber is for changing power into the span under test
Implementation Method 2
an optical receiver at the end of the multi-span link for measuring NLI on a per span basis
Implementation Method 3
the VOAs are 'dithered' for a particular span for determining the linear and nonlinear noise contributions for a particular span in a multi-span link
Data Source
AI summary
System and methods of measuring nonlinear interference (NLI) on a per-span basis in an optical system with a plurality of spans are provided. The method includes steps of varying power based on phase sensitive detection method on a span under test of the plurality of spans; observing total noise, at an optical receiver, from all of the plurality of spans; and isolating noise for the span under test from the total noise based on the varying power. The optical system can be in-service with one or more traffic-carrying channels, and the varying power is small enough on the span under test which does not impact the one or more traffic-carrying channels.