Tunable Dual-Peak LPFG Demodulation for Over-120-nm Cascaded FBG Sensing
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Solution Overview
Problem
Conventional demodulation methods for cascaded fiber Bragg gratings (FBGs) are limited in their ability to handle wide-wavelength range demodulation, particularly for six-axis multidimensional strain sensors, with demodulation ranges often falling short of the required 120 nm.
Innovation Solution
A demodulation method utilizing a tunable dual-peak resonance long-period fiber grating (LPFG) as a filter, coupled with a piezoelectric ceramic to control the spectrum, enabling wide-wavelength range demodulation by changing the transmittance spectrum and converting reflected light intensities into voltage values for precise center wavelength determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional LPFG is used for edge filtering, then the structure is simple and demodulation precision is high, but the spectral range is limited to less than tens of nanometers
Solution Approach 1:
The patent applies a tunable LPFG whose resonance wavelength can be dynamically adjusted by changing the refractive index of the surrounding medium. This dynamic tuning capability allows the filter to adapt to different spectral ranges, expanding the demodulation range from tens of nanometers to over 120 nm while maintaining high precision through controlled resonance conditions
Solution Approach 2:
The patent changes the resonance wavelength parameter of the LPFG by modifying the refractive index of the surrounding medium. This parameter change enables the same filter structure to operate across different spectral ranges, resolving the contradiction between fixed spectral range and adaptability requirement
2Adaptability or versatility
If the demodulation range is expanded to cover more than 120 nm, then the adaptability to wide-wavelength range demodulation is improved, but the complexity of the demodulation system increases
Solution Approach 1:
The patent designs a universal demodulation system using a tunable LPFG that can handle multiple FBGs across different wavelength ranges with a single filter component. The LPFG serves multiple functions: spectral filtering, wavelength tuning, and maintaining high precision demodulation, thereby expanding demodulation range without proportionally increasing system complexity
3Device complexity
If a tunable F-P or interferometer is used for edge filtering, then the demodulation range is small, but the structure is simple
Solution Approach 1:
The patent replaces traditional mechanical tuning methods (F-P cavity movement, interferometer adjustment) with a refractive index-based tuning mechanism for the LPFG. This substitution achieves wider demodulation range while maintaining structural simplicity, as the LPFG is a passive optical component that tunes through material property changes rather than mechanical adjustment
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 method achieves demodulation of seven cascaded FBGs with a range exceeding 120 nm, optimizing the optical path and maintaining high precision while reducing manufacturing costs, suitable for sensing signal analysis in spatial strain measurement.
Implementation Method 1
a piezoelectric ceramic 2, a dual-peak resonance LPFG 3... the piezoelectric ceramic 2 is controlled by the signal processing system 8 to move, so that the dual-peak resonance LPFG 3 fixed on the piezoelectric ceramic 2 bends and deforms
Implementation Method 2
a dual-peak resonance LPFG 3... configured to filter broadband laser emitted by the broadband light source 1 into a spectrum with four linear sidebands
Implementation Method 3
the dual-peak resonance LPFG 3 is used as a filter, and is configured to filter broadband laser emitted by the broadband light source 1 into a spectrum with four linear sidebands
Implementation Method 4
the photoelectric detector 7 is configured to: convert a sum of intensities of reflected light of the cascaded FBGs of the six-axis strain sensor 10 into a voltage value
Data Source
AI summary
Provided is a wide-wavelength range demodulation method for cascaded fiber Bragging gratings (FBGs) of a six-axis multidimensional strain sensor. Laser emitted by a broadband light source is filtered by a dual-peak resonance LPFG to form a transmittance spectrum; a piezoelectric ceramic is controlled by a signal processing system to move, so that a dual-peak resonance LPFG fixed on the piezoelectric ceramic bends and deforms, to change a spectrum filtered by the dual-peak resonance LPFG; and laser passing through the dual-peak resonance LPFG enters a circulator through an optical isolator and then is incident to the cascaded FBGs of the six-axis strain sensor; and reflected light of the cascaded FBGs enters a photoelectric detector through a circulator and an attenuator, the photoelectric converter is configured to: convert a sum of intensities of reflected light of the cascaded FBGs into a voltage value, input the voltage value into the signal processing system.