Phase-Shifted Fiber Grating Sensor for High Resolution Strain Measurement
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Solution Overview
Problem
Existing fiber grating sensor systems face challenges in accurately measuring small wavelength shifts due to limited sensitivity and resolution, particularly in detecting low amplitude high frequency signals such as those induced by acoustic or elastic waves.
Innovation Solution
The use of a phase-shifted fiber grating sensor with a narrow transmission spectral bandwidth, which increases the coherence length and allows for a larger wavelength-to-phase scale factor in the interferometer, enabling more precise measurement of small wavelength shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard fiber grating sensors with broad reflection bandwidth are used, then the sensor can reflect sufficient optical power for detection, but the coherence length is limited which reduces the wavelength-to-phase scale factor and measurement resolution
Solution Approach 1:
The reflection bandwidth is segmented into multiple narrow transmission spectral bands separated by reflection spectral bands. Each transmission band has a narrow bandwidth (e.g., 0.1 nm to 1 nm) which provides long coherence length, while the reflection bands provide sufficient reflected optical power. This segmentation allows the sensor to simultaneously achieve high measurement resolution through narrow transmission bands and sufficient signal strength through reflection bands.
Solution Approach 2:
Different spectral regions of the fiber grating sensor are assigned different functions: transmission spectral bands are optimized for high resolution measurements with narrow bandwidth providing long coherence length, while reflection spectral bands are optimized for providing sufficient optical power. This local differentiation of spectral regions allows simultaneous achievement of high precision and sufficient signal strength.
2Measurement precision
If the reflection bandwidth of the fiber grating sensor is narrowed to increase coherence length, then the wavelength-to-phase scale factor increases improving resolution, but the reflected optical power decreases
Solution Approach 1:
The spectrum is segmented into multiple narrow transmission bands (for high resolution) and multiple reflection bands (for sufficient power). By distributing the optical power across multiple reflection bands while maintaining narrow transmission bands for measurement, the system achieves both high resolution and sufficient reflected power.
Solution Approach 2:
Instead of narrowing the entire reflection bandwidth, the invention uses multiple partial transmission bands within the broader spectral range. Each transmission band is narrow enough for high resolution, but the cumulative effect of multiple bands provides sufficient transmitted and reflected power for detection.
3Productivity
If scanning type interrogators with coarse wavelength sampling steps are used, then the system is simpler and faster, but the measurement resolution is insufficient to detect small wavelength shifts from low amplitude high frequency signals
Solution Approach 1:
The invention replaces mechanical scanning wavelength tuning with a direct interferometric measurement approach. Instead of mechanically scanning through wavelengths with coarse steps, the narrow transmission bands enable direct interferometric detection where the long coherence length provides high sensitivity to small wavelength shifts, achieving both speed and precision.
Solution Approach 2:
The invention changes the spectral parameter of the fiber grating sensor by introducing multiple narrow transmission bands with specific bandwidths (0.1 nm to 1 nm). This parameter change in spectral bandwidth directly increases the coherence length and wavelength-to-phase scale factor, enabling high resolution detection without requiring fine scanning steps.
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 significantly improves the measurement resolution and accuracy of strain, temperature, or pressure, allowing for high-precision static and dynamic measurements.
Implementation Method 1
the structural periodicity causes one wavelength that matches the periodicity (i.e. periodic length of each structural period) to be reflected by the grating
Implementation Method 2
the interferometer is configured for separating from the optical output signal a first signal fraction and a second signal fraction, the interferometer including one or more optical elements for establishing a phase difference between the first signal fraction and the second signal fraction
Data Source
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AI summary
The invention is directed at a sensor arrangement for measuring a physical parameter. The sensor arrangement includes a fiber grating sensor and an optical sensor for determining a wavelength characteristic of an output signal from the fiber grating sensor. The optical sensor comprises a radiation source and an interferometer, wherein the interferometer is configured for providing a combined signal from two mutually phase delayed fractions of the output signal to an output port to generate an output interference signal for enabling determination of the wavelength characteristic by an analyzer operatively connectable to the output port via the calculation of the phase of the output interference signal. The fiber grating sensor is a phase shifted type fiber grating sensor. Thereby a sensor arrangement is provided having a very high measurement resolution, enabling highly accurate measurement of strain or pressure on a sample, both statically and dynamically.