Distributed Optical Fiber Sensor for Dynamic Stress Detection
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Solution Overview
Problem
Optical fiber-based distributed sensors face challenges in detecting low dynamic stresses in noisy environments due to sensitivity issues with slow disturbances from the environment, which limits their effectiveness in noisy conditions.
Innovation Solution
A distributed optical fiber sensor integrating a multimode optical fiber and an adaptive interferometer with a liquid-crystal light valve, which filters low-frequency noise and enhances sensitivity by using phase demodulation and dynamic holography to detect phase disturbances, allowing for improved detection of dynamic stresses in noisy environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical fiber-based distributed sensors are used in noisy environments, then they can detect dynamic stresses, but their sensitivity is degraded by slow environmental disturbances
Solution Approach 1:
The patent implements dynamic holographic recording where the liquid crystal light valve continuously updates the interference pattern in real-time, allowing the system to adapt to changing environmental conditions while maintaining sensitivity to dynamic stress signals. The dynamic nature of the holographic recording enables discrimination between static environmental disturbances and dynamic stress events.
Solution Approach 2:
The system uses periodic pulsed laser illumination to write holographic interference patterns at regular intervals. By comparing successive holographic recordings taken at different times, the system can identify and filter out slow environmental drifts while preserving detection of dynamic stress events that occur between pulses.
2Measurement precision
If the sensor uses phase demodulation to detect low dynamic stresses, then sensitivity improves, but the sensor becomes more susceptible to low-frequency noise
Solution Approach 1:
The liquid crystal light valve acts as an intermediary that records and stores the interference pattern holographically. This intermediary step allows the system to capture phase information with high sensitivity while the holographic nature of the recording inherently filters out low-frequency noise through the spatial averaging and temporal integration properties of holographic recording.
Solution Approach 2:
The patent replaces conventional direct phase detection methods with holographic interferometry, substituting a mechanical/optical measurement approach with a field-based holographic recording approach. This substitution enables phase demodulation with improved noise immunity because the holographic recording process naturally integrates and averages out low-frequency disturbances.
3Measurement precision
If the sensor integrates multimode optical fiber with adaptive interferometer, then spatial resolution and signal-to-noise ratio improve, but device complexity increases
Solution Approach 1:
The liquid crystal light valve serves multiple functions simultaneously: it acts as a beam splitter, a holographic recording medium, and a spatial modulator. The multimode optical fiber serves both as the sensing element and as a mode scrambler that provides spatial diversity. This multi-functionality reduces the need for additional separate components, thereby managing device complexity while maintaining improved spatial resolution and signal-to-noise ratio.
Solution Approach 2:
The patent merges the interferometer and holographic recorder into a single integrated adaptive interferometer system. By combining these functions in one apparatus using the liquid crystal light valve, the system achieves improved spatial resolution and noise filtering without proportionally increasing complexity, as the same physical component performs multiple critical functions.
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
The sensor achieves insensitivity to slow phase variations, enabling high sensitivity and noise filtering, and increases the signal-to-noise ratio by averaging over multiple propagation modes, effectively detecting low dynamic stresses with improved spatial resolution.
Implementation Method 1
a liquid crystal layer (3) disposed between a first substrate (11) and a second substrate (12), said light valve being characterised in that said first substrate (11) comprises a photoconductor material for said emission wavelength λ
Implementation Method 2
said first substrate (11) comprises a photoconductor material for said emission wavelength λ
Implementation Method 3
produce a series of interference zones corresponding to the interference between said reference beam Fr or a reference pulse Ipri and a signal optical pulse IpsiS arising from an output optical pulse Ipsi
Implementation Method 4
Distributed sensors are based on the processes of elastic and inelastic scattering in optical fibers
Implementation Method 5
architectures using the principle of Brillouin scattering have been much studied
Data Source
AI summary
A distributed optical fiber sensor of dynamic stress state comprises: an optical assembly configured to generate a series of optical pulses; an optical fiber of optical length L; an optical system configured to: inject through the first end at least the series of optical pulses; receive at the level of the end at least one series of output optical pulses, arising from the input pulses after propagation and retro-propagation in the fiber; generate at least one continuous reference beam or reference optical pulses on the basis of the optical assembly or of output optical pulses; produce a series of interference zones corresponding to the interference between the reference beam or a reference pulse and a signal optical pulse arising from an output optical pulse; a holographic detector comprising: a liquid-crystal light valve, the valve disposed so that it at least partially covers the interference zones, and producing holograms on the basis of the interference zones; at least one optical detector configured to detect output optical signals diffracted by the holograms.