Master-Slave OTDR Mapping for Long High Loss Fiber Spans
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Solution Overview
Problem
Current optical time-domain reflectometers (OTDRs) cannot measure the complete span distance, loss, or detect events across long fiber spans due to the requirement for over 64 dB of dynamic range, which exceeds their capabilities, leading to poor event spacing resolution and inability to map the entire fiber effectively.
Innovation Solution
A method involving a master and slave unit setup, where each unit measures the fiber length, infers a reference point, sets pulse width and measurement range, sends light pulses, crops and inverts traces, and combines them to create a complete and accurate map of the fiber, allowing for effective event detection and loss measurement across the entire span.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a single OTDR sends light pulses through a long fiber span to measure complete span distance and detect events, then the measurement coverage is improved, but the dynamic range requirement exceeds 64 dB which is beyond current product capabilities
Solution Approach 1:
The patent divides the long fiber span measurement into multiple segments by using two OTDRs (master and slave units) positioned at opposite ends of the fiber. Each OTDR measures a portion of the span, typically covering up to the midpoint or slightly beyond. The individual traces are then processed and combined to form a complete map of the entire fiber span, enabling measurement of long distances without requiring a single OTDR to have excessive dynamic range.
2Length of moving object
If wide pulse widths are used to send light pulses through long spans, then the measurement range is improved, but the event spacing resolution deteriorates with up to 2 km location uncertainty
Solution Approach 1:
The patent applies different pulse widths to different measurement segments based on local requirements. The master OTDR uses a first pulse width optimized for its measurement range, while the slave OTDR uses a second pulse width optimized for its segment. This allows each OTDR to use appropriate pulse widths for its specific measurement task, achieving both adequate range and resolution without requiring excessively wide pulses across the entire span.
3Measurement precision
If shorter pulse widths are used for better event location resolution, then the measurement precision is improved, but the ability to send light pulses through long spans deteriorates
Solution Approach 1:
The patent segments the long fiber span into multiple measurement zones, each handled by a different OTDR. This allows shorter pulse widths to be used in each segment to achieve good event location resolution, while the combined coverage of multiple OTDRs maintains the ability to measure the complete long span. Each OTDR operates within its optimized range rather than requiring one OTDR to cover the entire distance.
4Device complexity
If a single OTDR attempts to map the complete span, then the device complexity is reduced, but the measurement precision and event detection capability deteriorate
Solution Approach 1:
The patent combines the measurement capabilities of multiple OTDRs (master and slave units) to achieve complete span mapping with improved precision. The individual traces from each OTDR are processed through cropping, slope inversion, and combination algorithms to create a unified, accurate representation of the entire fiber span. This merging approach enables both complete coverage and high measurement precision that would be unattainable with a single OTDR.
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 measurement and mapping of long fiber spans with improved event detection and loss analysis, reducing the need for excessive dynamic range, enhancing resolution, and providing a cost-effective solution for fiber integrity assurance.
Implementation Method 1
measuring an end-to-end length of the fiber
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A method of tracing a complete span of a fiber includes inferring a reference point on the fiber based on a measured length of the fiber, setting a pulse width and a measurement range based on the inferred reference point, shooting a fiber from a master unit, attached to one end of the fiber, to collect trace past the inferred reference point, shooting a fiber from a slave unit, attached to an opposite end of the fiber, to collect trace past the inferred reference point, cropping the collected traces captured by the master unit and the slave unit past the inferred reference point, inverting a slope of the trace of the slave unit using measurement loss information and combining the trace of the master unit and the trace of the slave unit, with the inverted slope, to obtain a complete and accurate trace of the fiber.