Fiber Bragg Grating Temperature Compensation via Optical Filtering
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Solution Overview
Problem
Fiber optic sensors embedded with fiber Bragg gratings face interference from temperature fluctuations, which affect measurement accuracy when detecting mechanical variables like forces and pressures.
Innovation Solution
A method involving a first and at least one second fiber Bragg grating, where the Bragg wavelengths are influenced differently by mechanical quantities, using an optical filter device with rising and falling filter edges to filter secondary light, and evaluating the intensities to determine the mechanical quantity, thereby compensating for temperature effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fiber Bragg gratings are used to detect mechanical quantities, then measurement capability is provided, but temperature fluctuations affect measurement accuracy
Solution Approach 1:
The system divides the measurement function into two separate fiber Bragg gratings: one dedicated to temperature measurement and another to mechanical quantity measurement. This segmentation allows independent measurement of temperature and mechanical parameters, enabling subsequent compensation of temperature effects on the mechanical measurement to improve accuracy.
Solution Approach 2:
Temperature acts as an intermediary parameter that is explicitly measured by a dedicated fiber Bragg grating. By measuring temperature separately and using it to compensate the mechanical measurement from another grating, the system eliminates the harmful effect of temperature fluctuations on measurement accuracy.
2Measurement precision
If multiple fiber Bragg gratings are used for compensation, then temperature compensation is achieved, but device complexity increases
Solution Approach 1:
Multiple fiber Bragg gratings serve dual purposes: they individually detect their specific parameters (temperature or mechanical quantity) and collectively provide temperature compensation for the system. This multi-functionality achieves compensation without proportionally increasing system complexity.
Solution Approach 2:
The system uses identical fiber Bragg grating structures for both temperature and mechanical quantity sensing. By copying the grating design and using it for different measurement purposes, the system achieves compensation while maintaining structural simplicity and using standardized components.
3Loss of information
If optical filtering is applied to separate Bragg wavelengths, then signal separation is achieved, but optical system complexity increases
Solution Approach 1:
The optical filter device is designed with different filter characteristics at different wavelength regions. By optimizing the filter's local properties (rising and falling slopes) at specific wavelengths corresponding to the Bragg gratings, the system achieves effective signal separation without requiring complex filtering across the entire spectrum.
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 effectively compensates for temperature-induced interference, enhancing the accuracy of mechanical quantity detection by filtering and summing the intensities of secondary light from both gratings, allowing for precise measurement of mechanical variables.
Implementation Method 1
Filtering the first and second secondary light caused by the primary light and modified by the Bragg wavelength of the fiber Bragg gratings as a function of the mechanical quantity by means of an optical filter device with a rising and a falling filter slope
Implementation Method 2
The sensor elements integrated into fiber optic sensors are irradiated with optical radiation in a suitable wavelength range. Depending on the design of the sensor element and the mechanical force acting upon it, a portion of the incident light is reflected back by the sensor and can be fed to an evaluation and analysis unit. The applied force stretches the optical waveguide, changing the reflection or transmission wavelength of the fiber Bragg grating.
Data Source
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AI summary
The invention relates to a method for compensating, e.g. for compensating the temperature of a fibre-optic measuring system designed to detect a mechanical variable. First and second fibre Bragg gratings have a respective Bragg wavelength and the fibre Bragg gratings are irradiated with primary light. After the mechanical variable is applied to the first and second fibre Bragg gratings, the Bragg wavelengths of the fibre Bragg gratings are modified by the mechanical variable. The first and second secondary light that has been produced by the primary light and modified by the Bragg wavelength of the fibre Bragg grating in conjunction with the mechanical variable is filtered by means of an optical filter device, in such a way that the Bragg wavelength of the first fibre Bragg grating lies in the region of the rising filter edge and the Bragg wavelength of the second fibre Bragg grating lies in the region of the falling filter edge of the optical filter device. Once the intensities of the filtered first and second secondary light have been detected, said intensities are compared, as a result of which the mechanical variable can be determined from said intensity comparison.