Fibre Optic Rayleigh Sensing with Extended Reference Profiles
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Solution Overview
Problem
Existing frequency swept coherent Rayleigh sensing systems are limited by the need for a dedicated optical source arrangement and require a large number of interrogations, leading to a long time to acquire backscatter spectral profiles, and are prone to demodulation errors in continuous optical time domain reflectometry (COTDR) sensing.
Innovation Solution
A fibre optic sensing apparatus that operates in both frequency swept and COTDR modes, combining multiple backscatter spectral profiles to form a reference profile with an extended frequency range, allowing for efficient strain and temperature monitoring with reduced acquisition time and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If frequency swept coherent Rayleigh sensing is implemented with a dedicated optical source arrangement, then the frequency range can be extended, but the device complexity increases and acquisition time increases
Solution Approach 1:
The patent applies multi-functionality by enabling a single optical source to serve dual purposes: it can operate in traditional COTDR mode for continuous monitoring and in frequency-swept mode for extended frequency range analysis. The processor dynamically switches between these modes, eliminating the need for separate dedicated optical sources for each function and thereby reducing device complexity while maintaining versatility.
Solution Approach 2:
The patent utilizes parameter changes by modulating the optical frequency of the laser over time during frequency-swept mode operation. This frequency modulation enables the system to access a broader frequency range without requiring a dedicated optical source arranged for that specific purpose, thus extending capability while avoiding additional hardware complexity.
2Measurement precision
If a large number of interrogations are performed to acquire backscatter spectral profiles, then the frequency resolution improves, but the acquisition time increases
Solution Approach 1:
The patent implements periodic action by performing frequency-swept interrogations at regular intervals rather than continuously. The system alternates between frequency-swept mode for profile acquisition and COTDR mode for continuous monitoring, allowing the laser to be swept through frequency ranges periodically. This periodic approach achieves sufficient frequency resolution through multiple interrogations while controlling total acquisition time by not requiring continuous sweeping.
Solution Approach 2:
The patent applies preliminary action by acquiring backscatter spectral profiles at specific intervals before they are needed for continuous monitoring. By pre-acquiring these profiles during dedicated frequency-swept sessions, the system prepares reference data that can be used for subsequent strain and temperature detection without requiring continuous frequency sweeping, thus improving frequency resolution while managing acquisition time.
3Productivity
If continuous COTDR sensing is performed, then real-time monitoring is achieved, but demodulation errors occur
Solution Approach 1:
The patent implements feedback by periodically acquiring backscatter spectral profiles in frequency-swept mode and using these profiles to correct or validate the continuous COTDR monitoring data. The processor compares the spectral profiles obtained during frequency-swept mode with the continuous monitoring data, allowing for feedback-based correction of demodulation errors and improvement of measurement reliability while maintaining real-time monitoring capability.
Solution Approach 2:
The patent uses periodic action by alternating between frequency-swept mode for reference profile acquisition and COTDR mode for continuous monitoring. This periodic switching allows the system to maintain real-time monitoring through COTDR while periodically validating and correcting the data through frequency-swept spectral profile acquisition, thereby reducing demodulation errors without sacrificing continuous monitoring productivity.
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 efficient and accurate detection of strain and temperature changes over a broader frequency range by synthesizing backscatter spectral profiles, reducing the need for complex optical sources and minimizing demodulation errors.
Implementation Method 1
detecting and analysing optical radiation which is Rayleigh backscattered from within the sensing fibre
Implementation Method 2
A disturbance acting on the sensing fibre can result in a change in optical path length for the sensing portion, e.g. a physical change in length of that part of the sensing fibre
Implementation Method 3
a modulation of the refractive index, which can alter the distribution of the scattering sites
Data Source
AI summary
A fibre optic sensing apparatus (400) is described which has an optical output path (403, 405, 404) configured to repeatedly interrogate a sensing optical fibre (402) by launching coherent optical radiation into the sensing optical fibre. A detector (407) is configured to receive optical radiation that is Rayleigh backscattered from the sensing optical fibre and output a detected backscatter signal in response to each interrogation and a processor (408) processes the detected backscatter signal. The apparatus is operable in a frequency swept mode, in which the sensing optical fibre is interrogated with a first set of interrogations of coherent optical radiation having different optical frequencies from one another to acquire, for at least one sensing portion of the sensing optical fibre, a backscatter spectral profile (201) of a measurement value of the detected backscatter signal with frequency across a first frequency range. The processor is configured to combine a plurality of said backscatter spectral profiles (201, 202) to form a reference profile (203) with an effective frequency range greater than the first frequency range