OTDR Signal Insertion in PON Multistage Splitters
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Solution Overview
Problem
In Passive Optical Networks (PON), Optical Time-Domain Reflectometry (OTDR) measurements face challenges in accurately determining fault positions and severities due to low backscattered light levels and signal saturation, as well as difficulties in distinguishing between drop-branch faults after the splitter, leading to potential misinterpretations.
Innovation Solution
A method and client unit that trigger new OTDR measurements by inserting the signal into a multistage splitter before the last splitter stage of ratio 2:N, allowing for the calculation of fault magnitude by subtracting event magnitudes from reference measurements and accounting for the number of drop links, thereby enabling precise determination of fault positions and severities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the OTDR receiver circuit is made very sensitive to detect low backscattered light levels, then the detection sensitivity is improved, but big reflections will saturate or overload the receiver
Solution Approach 1:
The invention segments the PON network into multiple sections by inserting the OTDR measurement signal before the last splitter stage (2:N ratio). This allows the measurement to be divided into manageable segments, where each segment can be analyzed separately, preventing receiver saturation while maintaining detection sensitivity for low backscattered light levels.
Solution Approach 2:
The invention introduces an intermediary measurement approach by using a multistage splitter with a 2:N last stage. This intermediary structure allows the OTDR signal to be distributed in a controlled manner, enabling the receiver to handle reflections without saturation while still detecting weak backscattered signals from individual drop links.
2Reliability
If OTDR measurements are performed in a PON with multistage splitter, then the ability to monitor the network is improved, but the backscattered light from fibers between splitter and ONTs is attenuated making it difficult to obtain fault magnitude
Solution Approach 1:
The invention segments the measurement process by targeting the last splitter stage (2:N) specifically. By focusing the OTDR measurement on this final stage, the system can monitor the entire PON network while minimizing the cumulative attenuation effect of multiple splitter stages, thereby preserving the ability to measure fault magnitude accurately.
Solution Approach 2:
The invention changes the measurement dimension by inserting the OTDR signal at a specific point (before the last splitter stage) rather than at the beginning of the fiber chain. This dimensional shift in the measurement approach allows the system to overcome the cumulative attenuation problem while maintaining comprehensive network monitoring capability.
3Measurement precision
If OTDR measurements are performed after the splitter, then the ability to detect faults in drop links is improved, but it is impossible to define which specific drop-branch is affected as the received signal is a superposition from all drop links
Solution Approach 1:
The invention segments the superposition of signals from all drop links by focusing the measurement on the last splitter stage (2:N). This segmentation allows the system to distinguish between signals from different drop links, thereby identifying which specific branch is affected while maintaining the ability to detect faults in the entire network.
Solution Approach 2:
The invention extracts the measurement to a specific location (before the last splitter stage) where the signal superposition problem is minimized. By taking out the measurement from the conventional position and placing it at this intermediate point, the system can identify which specific drop-branch is affected while still monitoring all drop links.
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 enhances fault detection sensitivity and accuracy, allowing for targeted maintenance actions and reducing unnecessary maintenance efforts, while providing a cost-efficient solution for monitoring multiple OLTs with a single supervision system.
Implementation Method 1
Parts of the OTDR signals are reflected back towards the OTDR device. The back reflected, or backscattered, OTDR signal may be used for estimating the fiber's length and overall attenuation
Implementation Method 2
A Passive Optical Network, PON, is a point-to-multipoint network architecture employing fibre cables from a central office to premises. It employs unpowered optical splitters to enable a single optical fibre to serve multiple premises
Data Source
AI summary
A client unit and a method are provided performing fault analysis in a Passive Optical Network, PON, by using Optical Time Domain Reflectometry, OTDR. The method comprises triggering a new OTDR measurement, wherein a previous reference measurement has been made indicating an original state of the PON. The method further comprises inserting an OTDR measurement signal into a multistage splitter before a last splitter stage of the multistage splitter, and wherein the last splitter stage is of ratio 2:N; and obtaining at least one new event location based on the OTDR measurement signal. Further, the method comprises calculating a fault magnitude at a given location by subtracting an event magnitude obtained from the new OTDR measurement from the reference OTDR measurement and taking into account the number of drop links connected to the last splitter stage in the reference measurement and the new measurement. Thereby, determination of position and severity of the fault locations is enabled.