PON OTDR Measurement Noise Reduction via ONU Power Saving
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Solution Overview
Problem
The effectiveness of OTDR measurements in passive optical networks (PONs) is hindered by noise from optical network units (ONUs) leaking optical power, even when not transmitting, and the use of OTDR equipment can introduce interruptions in network operation.
Innovation Solution
An optical line terminal (OLT) is configured to place ONUs in a power-saving mode to reduce noise, allowing OTDR measurements to be performed without disrupting network operations, by transmitting a power-saving initiation command to ONUs and using a discovery slot to inject pulses for fault localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ONUs are kept in active state to maintain network operation, then network continuity is maintained, but optical power leakage creates noise that degrades OTDR measurement quality
Solution Approach 1:
The system uses periodic discovery slots within the PON frame structure to temporarily silence ONUs. During these scheduled intervals, ONUs are placed in a dormant state to eliminate optical power leakage noise, allowing OTDR measurements to be performed without interference. This periodic action resolves the contradiction by creating measurement windows while maintaining overall network operation between slots.
Solution Approach 2:
The OLT controller proactively places ONUs in a dormant state before initiating OTDR measurements. By preemptively silencing the ONUs and coordinating their inactivity with the measurement timing, the system ensures that no optical power leakage occurs during the critical measurement period, thereby guaranteeing measurement quality without disrupting network operation after the measurement is complete.
2Reliability
If OTDR pulses are injected into the PON to locate faults, then fault identification capability is improved, but network interruptions are caused that reduce service continuity
Solution Approach 1:
OTDR measurements are performed during periodic discovery slots that are part of the normal PON frame structure. These slots are specifically designed intervals where upstream traffic from ONUs is suspended, creating natural measurement windows. By injecting OTDR pulses during these pre-scheduled slots rather than arbitrarily, the system minimizes disruption to network services while maintaining the ability to perform fault location measurements.
Solution Approach 2:
The discovery slot acts as an intermediary mechanism that reconciles the conflicting needs of fault measurement and service continuity. During these slots, the system temporarily suspends normal upstream traffic to allow OTDR measurements, but the slots are brief and periodically interspersed with normal operation. This intermediary approach allows both fault identification and service continuity to coexist by compartmentalizing measurement activities to specific time windows.
3Measurement precision
If ONUs are placed in power-saving mode to reduce noise, then OTDR measurement quality is improved, but network power consumption increases for the OLT
Solution Approach 1:
The OLT places ONUs in power-saving mode only during brief discovery slots rather than continuously. This periodic activation of power-saving mode creates just enough silence for OTDR measurements without requiring the ONUs to remain in high-power states throughout operation. The OLT's power consumption increases only during these short measurement intervals, while the majority of the time ONUs operate in their normal low-power state, thus minimizing overall power impact.
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 the quality of OTDR measurements by reducing noise interference and minimizing disruptions to the PON, enabling accurate identification of faults such as faulty connectors or fiber breaks while maintaining network continuity.
Implementation Method 1
measuring the backscatter and reflection of light as a function of time
Implementation Method 2
measuring the backscatter and reflection of light as a function of time
Implementation Method 3
the pulse is injected into the PON by the optical transceiver at a wavelength of 1,490 nanometers (nm), 1,550 nm, 1650 nm, or 1310 nm
Data Source
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AI summary
In a first aspect, the method and apparatus of the present disclosure can be used to periodically and/or intermittently place one or more ONUs attached to a PON in a power savings mode so that an OTDR test can be performed. While in the power savings mode, the ONUs temporarily suspend their transmitter function and power down their upstream lasers. In a second aspect, the method and apparatus of the present disclosure can be used to coordinate the performance of OTDR during one or more periodic or intermittent discovery slots used to detect and register ONUs recently connected to the PON. Because new ONUs are infrequently connected to the PON and ONUs already registered are not permitted to transmit during the discovery windows, OTDR can be performed during these windows without impacting, to a great degree, the normal operation of the PON.