Self-Referenced Fiber Laser Sensor for Stress Measurement
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Solution Overview
Problem
Current fiber optic sensors for measuring physical quantities, such as stress and pressure, require complex interrogation systems due to the need for phase shift measurement, often involving interferometers or reference sensors, which complicates the architecture.
Innovation Solution
The development of self-referenced active fiber sensors using Bragg gratings and fiber lasers that generate two optical waves of different frequencies, allowing direct measurement of the frequency difference between these waves to determine the measured quantity, eliminating the need for interferometric modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric methods or reference sensors are used to measure phase shift, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts the reference wave generation function from external interferometric equipment and integrates it directly into the fiber optic sensor itself. The Bragg grating reflects part of the optical signal to create an inherent reference wave, eliminating the need for separate reference sensors or complex interferometric benches while maintaining measurement precision.
Solution Approach 2:
The patent merges the sensing function and reference wave generation function into a single integrated sensor unit. The Bragg grating serves dual purposes: it acts as both the sensing element that experiences phase shift from physical quantities and the reference wave generator, thereby simplifying the overall device architecture.
2Device complexity
If self-referenced active fiber sensors are used, then device complexity is reduced, but measurement precision may be affected
Solution Approach 1:
The patent uses optical frequency difference as an intermediary parameter to bridge the simplified sensor structure and precise measurement requirements. Instead of directly measuring phase shift, the system measures the frequency difference between the optical waves, which is directly related to the physical quantity and can be measured with high precision using standard frequency counters.
Solution Approach 2:
The patent changes the measurement parameter from phase shift to optical frequency difference. This parameter transformation allows the use of a simpler sensor structure while maintaining measurement precision, as frequency difference can be accurately measured using standard electronic frequency counters without requiring complex interferometric equipment.
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 simplifies the sensor architecture by eliminating the need for interferometric modules, enabling more straightforward and efficient measurement of physical quantities like stress and pressure, with improved sensitivity and reduced complexity.
Implementation Method 1
the fiber comprising at least one Bragg grating, the fiber is arranged so as to generate in the amplifying medium two optical waves of different optical frequency, propagating in the same direction after reflection on the Bragg grating
Implementation Method 2
a measuring optical fiber comprising a doped amplifying medium whose optical characteristics are sensitive to a physical quantity, optical pumping means of said amplifying medium ensuring the population inversion of said medium and the generation of the two optical waves
Data Source
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AI summary
The invention generally pertains to the field of optical fibre sensors including at least one measurement optical fibre (10) containing an optically-pumped doped amplification medium (11) having optical characteristics that are sensitive to a physical value, the fibre including at least one Bragg grating (12). The fibre is adapted so as to generate, in the amplification medium, at least two optical waves (1, 2) having different optical frequencies, propagating in the same direction after reflection on the Bragg grating and transmitted by the amplification medium, wherein the two optical frequencies depend on the physical value. The generation of the two waves can be made using a birefringent polarisation-supporting fibre, or a laser cavity of the DBR (Distributed Bragg Reflector) type. The sensor can particularly be used as a hydrophone.