Nested Control Loops for Optical Network Gain Stability
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Solution Overview
Problem
Fiber-optic transmission networks face instability and overshoot issues due to concatenated optical power-control loops reacting to events at individual nodes, leading to over-compensation and prolonged event effects.
Innovation Solution
Implementing two nested control loops with different update speeds: an inner, faster control-loop for maintaining constant node gain and an outer, slower control-loop for maintaining constant output power, allowing for automated adaptation to physical-layer variability and dynamic changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple optical power-control loops are concatenated in series to counter individual power changes at each node, then each node can maintain its power stability, but the combined response causes over-reaction and overshoot
Solution Approach 1:
The patent segments the power control function into two distinct control loops: an inner loop that maintains constant node gain and an outer loop that maintains constant output power. This segmentation allows each loop to have a specific, limited function rather than trying to handle all power control aspects, thereby preventing over-reaction while maintaining stability.
Solution Approach 2:
The patent implements a nested control structure where the inner constant node gain loop is embedded within the outer constant output power loop. The inner loop operates at a faster update rate and provides immediate response to gain changes, while the outer loop operates at a slower rate to maintain overall output power stability. This nesting resolves the contradiction by having coordinated, hierarchical control rather than independent concatenated loops.
2Speed
If control loops operate at high speed to respond quickly to power changes, then response time is improved, but overshoot and instability increase
Solution Approach 1:
The patent applies dynamic control by assigning different update rates to different control loops. The inner constant node gain loop operates at a faster speed to quickly correct gain deviations, while the outer constant output power loop operates at a slower speed to make gradual adjustments to output power. This dynamic, multi-rate control structure allows the system to respond quickly to immediate disturbances while avoiding overshoot through the damping effect of the slower outer loop.
3Measurement precision
If automated power control loops are implemented to maintain target powers, then power accuracy is improved, but the system becomes complex and prone to over-reaction
Solution Approach 1:
The patent segments the automated power control into two specialized loops with distinct objectives: the inner loop focuses exclusively on maintaining constant node gain, while the outer loop focuses on maintaining constant output power. This segmentation simplifies each individual loop's control algorithm and makes the overall system more manageable despite the automation, as each loop has a clear, limited function rather than trying to handle all power control variables simultaneously.
Data Source
AI summary
The present invention provides methods and systems to stabilize an optical network against nodal gain changes through two nested control loops for controlling node gain and node output power. The present invention includes two nested control-loops running at different update speeds including: an inner, faster, control-loop which sets the gains and losses within a node to achieve a node-gain target, and a node-gain target for the inner loop is set by an outer, slower, control loop that whose target is the node output power. Advantageously, the present invention reduces the problem of concatenated overshoot by minimizing the control-loop response to events that occur at other nodes.