Optical Sensor for Fiber Grating Interrogation
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Solution Overview
Problem
Existing fiber grating sensor interrogation methods lack sufficient sensitivity to detect small strain variations, particularly low amplitude high frequency signals, due to coarse wavelength sampling and high phase noise levels.
Innovation Solution
An optical sensor system utilizing a radiation source with discrete wavelengths overlapping with the fiber grating sensor's spectral bandwidth, coupled with an interferometer that splits and recombines the signal to reduce phase noise and enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard interrogation technologies (scanning laser, scanning optical filter, spectrometer) are used, then the system is easier to operate, but the measurement precision is insufficient for detecting small strain variations
Solution Approach 1:
The optical spectrum is segmented into multiple discrete wavelength channels using a frequency comb source, allowing parallel measurement of multiple wavelength points simultaneously. This segmentation enables fine wavelength sampling without requiring sequential scanning, thereby improving measurement precision while maintaining system simplicity.
Solution Approach 2:
The patent replaces mechanical scanning systems (scanning laser, scanning optical filter) with a stationary interferometric measurement system using frequency comb source. This substitution eliminates mechanical moving parts, reducing system complexity while achieving higher measurement precision through parallel wavelength channel analysis.
2Measurement precision
If fine wavelength sampling is implemented, then the measurement precision improves, but the measurement time increases due to more wavelength steps
Solution Approach 1:
The frequency comb source generates periodic spectral lines at fixed intervals, creating a regular sampling pattern across the wavelength range. This periodic structure allows the system to achieve fine wavelength sampling with a fixed number of discrete channels, enabling rapid parallel measurement without increasing measurement time.
Solution Approach 2:
The interferometric measurement system continuously monitors all wavelength channels simultaneously using the frequency comb source, maintaining continuous useful action across the entire spectral range. This eliminates the need for sequential scanning, achieving fine wavelength sampling with constant measurement speed.
3Measurement precision
If continuous spectrum radiation source is used, then the device complexity is lower, but the phase noise level is higher reducing sensitivity
Solution Approach 1:
The continuous spectrum is segmented into discrete frequency comb lines, isolating specific wavelength channels for measurement. This segmentation reduces phase noise by eliminating interference from adjacent wavelengths, improving measurement precision while the frequency comb source maintains manageable device complexity.
Solution Approach 2:
The patent extracts only the necessary discrete wavelength components from the continuous spectrum using frequency comb generation. This extraction removes harmful phase noise components while retaining the useful spectral information, achieving low phase noise levels without requiring a fundamentally complex radiation source.
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 system achieves significantly improved sensitivity to small wavelength shifts, allowing for the detection of smaller strain variations with reduced noise interference, thereby enhancing the accuracy of strain measurements.
Implementation Method 1
the fiber grating sensor comprises a fiber section including an internal structural periodicity such as to reflect, upon receiving an optical interrogation signal in use, optical radiation at a reflection wavelength that is dependent on the internal structural periodicity
Implementation Method 2
the interferometer is configured for splitting the optical output signal into a first signal fraction and a second signal fraction... and combines the first and second signal fraction from the first and second branch into a combined signal to generate interference
Data Source
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AI summary
The invention is directed at an optical sensor for interrogating a fiber grating sensor for determining a wavelength characteristic of an optical output signal. The optical sensor comprises a radiation source for illuminating the fiber grating sensor with an optical interrogation signal, an interferometer, and an optical conveyance structure. The interferometer is configured for splitting the optical output signal into a first and second signal fraction, and includes a first and second branch for conveying the first and second signal fraction, which branches are of different length to establish a path length difference. The interferometer is further configured for combining the signal fractions and for providing the combined signal to an output port for determination of the wavelength characteristic by an analyzer. The radiation source provides an optical radiation signal at discrete wavelengths, which include at least three wavelengths overlapping with a spectral bandwidth of the fiber grating sensor.