Embedded OTDR Testing in TWDM PON Networks
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Solution Overview
Problem
Existing OTDR systems for TWDM PONs require dedicated hardware and cause service disruptions during testing, fail to detect impairments affecting regular service, and are costly due to the need for external headends and couplers.
Innovation Solution
An embedded OTDR test system that selects an in-service TWDM channel for testing, using existing transceivers and lasers to minimize impact on users, avoiding service interruptions and using an in-service wavelength for improved accuracy and reduced deployment costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated headend with transceiver, couplers and optical switch is deployed for OTDR testing, then the detection capability is improved, but the deployment cost and complexity increase
Solution Approach 1:
The existing downstream laser transmitters in the TWDM PON are made to serve dual purposes: normal data transmission and OTDR testing. The control unit enables the laser to function as an OTDR pulse generator by modulating it with OTDR pulses, eliminating the need for dedicated test equipment and reducing deployment complexity while maintaining detection capability
Solution Approach 2:
The patent merges the OTDR testing function with the existing downstream transmission infrastructure. By combining the laser transmitter, modulator, and receiver into a unified system that handles both data and test functions, the patent reduces the number of separate components needed, thereby simplifying deployment while preserving reliable detection
2Reliability
If couplers are inserted before activating the TWDM PON for OTDR testing, then the testing capability is established, but service activation is delayed and deployment becomes more challenging
Solution Approach 1:
The system performs OTDR testing after the PON is already activated and operational, rather than requiring pre-installation of test equipment. The control unit enables testing to be conducted on-demand by dynamically configuring existing resources, allowing service activation to proceed without delay while testing capability is established through software control rather than physical pre-deployment
3Reliability
If a reserved dedicated wavelength is used for OTDR testing, then the test signal can be separated from data signals, but the testing does not reflect actual service conditions and may miss service-affecting impairments
Solution Approach 1:
The system uses time-division multiplexing to alternate between data transmission and OTDR testing on the same wavelength. The modulator switches the laser between normal data mode and OTDR pulse mode in periodic intervals, allowing both functions to share the wavelength without interference while ensuring testing occurs under actual service conditions
Solution Approach 2:
The patent dynamically assigns wavelengths for OTDR testing based on current PON status and service requirements. Rather than reserving a fixed wavelength, the system can select from available wavelengths dynamically, ensuring that testing occurs on wavelengths actually used for service while maintaining signal separation through temporal and spectral management
4Device complexity
If existing lasers are reused to transmit OTDR pulses instead of using dedicated test equipment, then deployment cost is reduced, but the impact on regular users increases
Solution Approach 1:
The modulator implements periodic switching between data transmission and OTDR pulse generation, with sufficient spacing between test pulses to allow data traffic to resume. This temporal separation ensures that OTDR testing occurs in brief intervals without持续 disrupting user service, while still achieving comprehensive fiber diagnostics
Solution Approach 2:
The control unit dynamically adjusts the testing schedule and wavelength selection based on real-time PON status, traffic patterns, and service requirements. By adapting when and where testing occurs, the system minimizes impact on users while maintaining cost-effective reuse of existing laser resources
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
Enables faster and more accurate detection of physical impairments with reduced deployment challenges and costs, as it reuses existing hardware and does not require external equipment, allowing for parallel testing of multiple PONs without service interruptions.
Implementation Method 1
capture reflections of the OTDR test signal at the OLT
Data Source
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AI summary
An optical time domain reflectometry (OTDR) test system detects a physical impairment in a TWDM PON in operational use by a service provider, and thereto comprises a processor (107; 207; 307; 407) configured to: - assess the status of the TWDM PON; - select a test channel amongst the available TWDM channels for an OTDR test through an optimization criterion minimizing impact for one or more users; - move optical network terminations or ONTs (171, 175; 271, 275; 371, 275; 471, 475) that are using the test channel to alternate TWDM channels; - instruct injection of an OTDR test signal by the respective laser (121; 221; 321; 421) in the optical line termination or OLT (101; 201; 301; 401) into the test channel; - capture reflections of the OTDR test signal at the OLT (101; 201; 301; 401); - move the ONTs (171, 175; 271, 275; 371, 275; 471, 475) back to the test channel or a more optimal channel configuration; and - process the reflections of the OTDR test signal to detect the physical impairment.