In-service Per-span NLI Measurement via Optical Receiver
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Solution Overview
Problem
Existing methods for characterizing nonlinear interference (NLI) in optical fiber communication systems are limited, as they require implementation at commissioning and do not allow for in-service characterization on a per-span basis. Additionally, current power control approaches in optical systems rely on modeling, which is prone to errors due to provisioned or measured parameters that may not reflect real system performance.
Innovation Solution
The proposed solution involves using an optical receiver at the end of a multi-span link to measure NLI on a per-span basis. This is achieved by employing a pair of variable optical attenuators (VOAs) before and after each span, allowing for power adjustments that isolate NLI contributions. The method also includes phase sensitive detection with shallow dithering to accurately measure small changes in noise-to-signal ratio (NSR) without disrupting in-service channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If per-span NLI characterization is implemented at commissioning using existing methods, then fiber nonlinear parameters can be measured, but the system cannot perform in-service characterization once the optical link is operational
Solution Approach 1:
The patent introduces a probe signal as an intermediary carrier to transport NLI measurement information through the optical link without disrupting traffic channels. The probe signal interacts with the fiber nonlinearity and carries the measured NLI characteristics back to the receiver, enabling in-service measurement capability that was previously unavailable
Solution Approach 2:
The patent segments the total NLI measurement into per-span contributions by using multiple probe signals at different power levels and analyzing the differential measurements. This allows isolation and characterization of individual span nonlinearities within the multi-span link, achieving per-span resolution during in-service operation
2Productivity
If modeling-based power control is used with provisioned or measured parameters, then optimal launch power can be calculated, but errors accumulate from parameter inaccuracies and modeling complexity
Solution Approach 1:
The patent implements a feedback mechanism where the actual NLI measurements from the optical link are used to update and refine the launch power optimization. The measured NLI values provide direct feedback about the true system behavior, allowing the control system to adjust launch powers based on actual performance rather than relying solely on modeled predictions with uncertain parameters
Solution Approach 2:
The system uses its own transmitted probe signals to self-characterize the fiber nonlinearities and determine optimal operating conditions. The optical link itself provides the measurement medium, eliminating the need for external characterization equipment or reliance on factory-calibrated parameters that may not reflect field conditions
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 per-span NLI, allowing for optimized operating conditions, validation of noise modeling, and confirmation of restoration path viability. It also facilitates localized launch power control for network-level optimization, minimizing errors and improving system performance.
Implementation Method 1
An enabler is to have 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, such that NLI generated by the span under test will be changed
Implementation Method 2
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. This data is important for predicting the performance of the link
Implementation Method 3
The noise that develops in each amplified span primary consists of amplified spontaneous emission (ASE) and NLI. ASE depends on amplifier gain and can be predicted with high accuracy given our knowledge of the amplifier parameters and the optical power
Implementation Method 4
NLI is more challenging to estimate because it depends on properties of the optical fiber which are often unknown or can be mis-provisioned
Data Source
AI summary
Systems and methods for in-service measurement of nonlinear interference on a per span basis in an optical network having a plurality of spans include steps of varying power in a span of the plurality of spans to cause small power perturbations which do not impact traffic carrying signals; observing a change in noise at an optical receiver at an end of the plurality of spans with the change due to the varying the power in the span; and determining the nonlinear interference for the span based on the change in the noise.