Fibre-Optic Sensing Dynamic Range Extension
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Solution Overview
Problem
Fibre optic sensing systems face limitations in dynamic range, particularly in measuring strain signals due to signal aliasing caused by acoustic waves of varying amplitudes, which prevents accurate phase unwrapping and reconstruction of strain signals in applications like seismic measurement.
Innovation Solution
The use of a second optical fibre with different acoustic sensitivity, combined with a first optical fibre, allows for the processing of phase signals to distinguish and separate the original and additional phase signals, enabling the reconstruction of strain measurements by employing phase unwrapping techniques and gain adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single optical fibre is used with fixed amplitude sensitivity, then the system structure remains simple, but the dynamic range is insufficient and signal aliasing occurs when exposed to acoustic waves of different amplitudes
Solution Approach 1:
The patent divides the sensing system into multiple optical fibres, each with different amplitude sensitivities. The first optical fibre is optimized for detecting high-amplitude acoustic waves, while the second optical fibre is optimized for detecting low-amplitude acoustic waves. This segmentation allows the system to handle a wider dynamic range by assigning different detection ranges to different fibres, resolving the contradiction between adaptability and complexity.
Solution Approach 2:
The patent changes the amplitude sensitivity parameter of the optical fibres by using fibres with different core diameters or different coating properties. This parameter variation enables each fibre to respond differently to acoustic wave amplitudes, allowing the system to capture both high-amplitude and low-amplitude signals without aliasing, thus improving dynamic range while maintaining a relatively simple structure.
2Measurement precision
If acoustic signals of higher amplitude are detected, then the amplitude sensitivity is improved, but signal saturation occurs and phase data processing techniques cannot be applied
Solution Approach 1:
The patent segments the amplitude detection range by using multiple optical fibres with different sensitivities. The first optical fibre with higher amplitude sensitivity is used for detecting high-amplitude acoustic waves, while the second optical fibre with lower amplitude sensitivity handles low-amplitude signals. This prevents signal saturation in each fibre by matching the fibre's sensitivity to the appropriate signal range, ensuring reliable detection across the full dynamic range.
Solution Approach 2:
The patent introduces a signal processing unit that acts as an intermediary to select and combine phase data from different optical fibres based on the acoustic wave amplitude. This intermediary processing ensures that the appropriate fibre data is used for each signal level, preventing saturation artifacts and maintaining measurement precision across all amplitude ranges.
3Measurement precision
If phase unwrapping techniques are applied to reconstruct strain signals, then measurement precision is improved, but the technique fails when phase data is aliased due to high-rate phase variation
Solution Approach 1:
The patent segments the phase measurement process by using multiple optical fibres that produce phase data at different rates of change. The first optical fibre produces phase data that varies more slowly with acoustic wave amplitude, making it suitable for phase unwrapping at high amplitudes. The second optical fibre produces phase data that varies more quickly, suitable for low amplitudes. This segmentation prevents phase aliasing by ensuring that each fibre operates within its optimal phase variation range.
Solution Approach 2:
The patent applies preliminary selection of phase data from the appropriate optical fibre based on the acoustic wave amplitude before attempting phase unwrapping. By pre-selecting the fibre whose phase data rate is appropriate for the current signal level, the system ensures that phase unwrapping can be successfully applied without aliasing errors, thereby improving strain signal reconstruction precision.
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 dynamic range of fibre optic sensors, allowing for the accurate reconstruction of strain signals even in the presence of varying acoustic wave amplitudes, improving signal linearity and quality by combining fibres with different sensitivity ranges.
Implementation Method 1
distributed fibre optic sensing systems measure, for example, the amplitude of Rayleigh backscatter returned from the fibre optic sensor when excited by the pulses of light
Implementation Method 2
The rate of change of a signal, for example the phase of the optical signal, depends on its amplitude and frequency
Data Source
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AI summary
Processing strain measurement signals from a first measured signal representing a first received backscattered optical signal for a first sensor - the first measured signal associated with a first phase signal - and a second measured signal representing a second received backscattered optical signal for a second sensor. The second measured signal is associated with a second phase signal constituting a consolidation of the first phase signal and an additional phase signal - where the additional phase signal is unrecoverable from the first measured signal. The first phase signal is determined from the first measured signal and processed. The second phase signal is determined from the second measured signal, where the first phase signal and additional phase signal are indistinguishable in the phase domain. The second phase signal is processed to obtain the additional phase signal and a strain measurement signal is constructed using the processed first phase signal and additional phase signal.