Distributed Fiber Sensing Pulse Pair Generation
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Solution Overview
Problem
Distributed fiber sensing configurations face limitations in detecting back-scattered signals due to ultra-narrow linewidth requirements in coherent detection, which restrict the measurement range and resolution, and are affected by phase noise increasing with fiber length.
Innovation Solution
A distributed fiber sensing system that generates pairs of ultra-narrow linewidth interrogating pulses with a time delay, allowing direct detection without mixing signals, and an alternative configuration using a local oscillator to analyze phase differences between consecutive pulses, reducing phase noise and eliminating coherence length scaling with fiber length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent detection with local oscillator mixing is used to detect weak back-scattered signals, then measurement sensitivity is improved, but ultra-narrow linewidth requirements limit the measurement range and resolution
Solution Approach 1:
The patent extracts and eliminates the local oscillator mixing step from the detection process. By using direct detection of back-scattered signals without coherent mixing, the system removes the ultra-narrow linewidth requirement that plagues coherent detection systems, while still maintaining the ability to detect weak signals through advanced signal processing of the directly detected optical intensity
Solution Approach 2:
The patent substitutes the mechanical/optical mixing process (coherent detection with local oscillator) with a direct detection approach combined with electronic signal processing. This replacement eliminates the need for precise optical phase matching and ultra-narrow linewidth lasers, replacing complex optical mixing with more tolerant electronic processing of intensity signals
2Measurement precision
If interrogating pulse power is increased to enhance back-scattered signal energy, then signal-to-noise ratio is improved, but non-linear optical phenomena appear at higher pulse powers
Solution Approach 1:
The patent uses Rayleigh back-scattered light as a copy of the interrogating pulse characteristics to infer events along the fiber. By analyzing the properties of this back-scattered copy rather than directly measuring high-power interactions, the system achieves high sensitivity without exposing the fiber to power levels that would trigger non-linear effects
Solution Approach 2:
The patent introduces Rayleigh back-scattered light as an intermediary that carries information about the interrogating pulse and fiber events. This intermediary allows the system to probe the fiber with low power while still extracting high-quality measurement data from the scattered light, avoiding direct high-power interaction that would cause non-linear phenomena
3Measurement precision
If pulse duration of interrogating pulse is increased to enhance signal energy, then back-scattered signal power is improved, but resolution is reduced
Solution Approach 1:
The patent employs dynamic time-gating and signal processing techniques to resolve the trade-off between pulse duration and resolution. By using short interrogating pulses combined with advanced temporal signal processing and multiple measurement sequences, the system achieves both high signal energy accumulation and fine spatial resolution that would be impossible with a single static pulse configuration
4Productivity
If multiple interrogating pulses are transmitted at repetition rate faster than single roundtrip time, then measurement speed is improved, but ambiguity in detecting signal locations occurs
Solution Approach 1:
The patent uses periodic transmission of interrogating pulses with carefully controlled repetition rates and timing sequences. By implementing multi-sequence periodic measurements with varying time delays and using cross-correlation processing between sequences, the system achieves high-speed measurements at repetition rates exceeding the single roundtrip time while eliminating location ambiguity through the periodic pattern analysis
Solution Approach 2:
The patent implements feedback-based signal processing where the detected back-scattered signals from multiple pulses are processed in sequence with reference to known transmission timing. The system uses the temporal patterns and correlations between multiple periodic pulse responses to resolve ambiguous location information, providing feedback-driven disambiguation that enables high-speed operation without loss of spatial information
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 detection and measurement of back-scattered signals without ultra-narrow linewidth limitations, improving resolution and reducing phase noise, allowing for longer sensing fiber lengths without coherence length scaling, thus enhancing measurement accuracy and range.
Implementation Method 1
back-scattered signals in the optical fiber
Implementation Method 2
modulator generates a plurality of pairs of interrogating pulses having a time delay, where a frequency difference between two pulses of the same interrogating pair
Implementation Method 3
detector with a predetermined detection bandwidth for detecting back-scattered signals
Data Source
AI summary
Distributed fiber sensing system including a laser source, a circulator, a detector and an optical fiber, the circulator coupled with the laser source, the detector and the optical fiber, the laser source for generating at least two ultra-narrow linewidth interrogating pulses, the detector having a predetermined detection bandwidth for detecting back-scattered signals, the laser source including an ultra-narrow linewidth laser and a modulator, coupled with the ultra-narrow linewidth laser and the circulator, the modulator generating a plurality of pairs of interrogating pulses having a time delay, a frequency difference between two pulses of the same interrogating pair being less than the predetermined detection bandwidth and a frequency difference between two pulses not of the same interrogating pair being larger than the predetermined detection bandwidth, wherein the optical fiber can be characterized based on beat-notes between back-scattered signals originating from the pair of interrogating pulses detected by the detector.