Dual-Wavelength Fabry-Perot Sensor for Acoustic Pressure
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Solution Overview
Problem
Fiber optic sensor systems using Fabry-Perot interferometers face challenges such as power fluctuations and time-dependent polarization effects, which hinder the effective sensing of acoustic pressure in fiber optic sensor arrays.
Innovation Solution
A two-wavelength Fabry-Perot interferometric sensor system with a time division multiplexed or fan-out architecture, utilizing optical couplers and photodetectors to detect signals of different wavelengths, and incorporating a diaphragm with a fluid-filled gap in a single mode optical fiber to modulate the distance and reflectivity in response to acoustic pressure, thereby stabilizing the sensor response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Fabry-Perot interferometer is used in a fiber optic sensor array, then acoustic pressure sensing capability is provided, but power fluctuations and polarization effects cause measurement instability
Solution Approach 1:
The patent uses two different wavelengths (λ1 and λ2) to interrogate the Fabry-Perot interferometer. By measuring the phase shift at both wavelengths and combining the information, the system achieves immunity to power fluctuations and polarization effects. The dual-wavelength approach transforms a single-parameter measurement into a multi-parameter measurement that can distinguish between acoustic pressure changes and environmental disturbances.
Solution Approach 2:
The system employs a feedback mechanism where the measured intensities at two wavelengths are used to calculate the acoustic pressure in a way that compensates for power fluctuations. The ratio or difference of the two wavelength signals provides feedback information that cancels out common-mode disturbances, ensuring stable measurements.
2Device complexity
If a single wavelength is used in the Fabry-Perot sensor, then the system is simpler, but it cannot overcome power fluctuations and polarization effects
Solution Approach 1:
The patent introduces a second wavelength parameter to the measurement system. This additional parameter enables the system to differentiate between actual acoustic pressure changes and artifacts caused by power fluctuations or polarization effects, thereby improving measurement accuracy without requiring complex hardware modifications.
Solution Approach 2:
The dual-wavelength Fabry-Perot sensor performs multiple functions simultaneously: it measures acoustic pressure while also compensating for power fluctuations and polarization effects. This multi-functionality is achieved through the mathematical processing of the two wavelength signals, which can separate the acoustic information from the environmental disturbances.
3Reliability
If optical power fluctuations occur in the fiber optic system, then source laser stability is compromised, but the sensor can still function with proper compensation
Solution Approach 1:
The patent measures the Fabry-Perot interferometer response at two different wavelengths. By taking the ratio or difference of these two measurements, the system creates a metric that is insensitive to overall power fluctuations. This approach transforms the problem of power instability into an opportunity for differential measurement that cancels out the fluctuations.
Solution Approach 2:
The second wavelength measurement acts as an intermediary that mediates the effect of power fluctuations. By introducing this additional measurement channel, the system can mathematically eliminate the influence of power variations on the final acoustic pressure calculation.
4Stability of the object's composition
If time-dependent polarization effects are present in the fiber, then measurement consistency deteriorates, but dual-wavelength measurement compensates for this
Solution Approach 1:
The patent employs two wavelengths that are sensitive to polarization effects in different ways. By combining the measurements from both wavelengths, the system creates a composite signal that is insensitive to time-dependent polarization changes. This works because the polarization effects manifest differently at the two wavelengths, allowing their effects to be mathematically separated and eliminated.
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 configuration overcomes power fluctuations and polarization effects, providing a stable and linear response to acoustic pressure changes, with improved sensitivity and reduced harmonic distortion, enabling effective acoustic pressure sensing in fiber optic sensor arrays.
Implementation Method 1
A two-wavelength Fabry-Perot interferometric sensor system with a time division multiplexed or fan-out architecture, utilizing optical couplers and photodetectors to detect signals of different wavelengths
Implementation Method 2
an end of a multimode core arranged such that optical signals of wavelength λA and λB propagating in the single mode optical fiber undergo multiple reflections and produce a diverging light beam comprising interference signals
Implementation Method 3
the diaphragm being movable with respect to the end of the single mode optical fiber to modulate the distance between the diaphragm and end of the single mode optical fiber in response to pressure the diaphragm and end of the single mode optical fiber in response to pressure variations in the acoustic pressure wave
Implementation Method 4
a corresponding second photodetector arranged to detect signals of wavelength λB
Data Source
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AI summary
Two optical wavelengths are used to interrogate a fiber optic Fabry-Perot sensor ( 1-4) having a moveable diaphragm (34) that changes the width of a gap (36) between two reflective surfaces (38, 40). By picking the right operating point for the gap (36), the power output for one wavelength increases as the gap width changes and the power for the other wavelength decreases. A ratio of the difference of the two powers over the sum of the two powers is formed to generate a detected signal independent of power and phase fluctuations in a fiber (22) between signal sources (46, 48) and sensor (1-4) and between sensor ( 1-4) and detector (73). This ratio, which is called the visibility, has a response proportional to the pressure of acoustic disturbances that move the diaphragm (34). The push-pull sensor ( 1-4) can be used with both TDM and CW fan-out array architectures (45, 47).