Brillouin Scattering Signal Processing for Fiber Monitoring
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Solution Overview
Problem
Existing optoelectronic devices for distributed measurement by Brillouin scattering in optical fibers are complex, energy-intensive, and not suitable for autonomous operation, limiting their ability to continuously monitor isolated civil engineering structures with high spatial resolution and low energy consumption.
Innovation Solution
A compact, energy-efficient optoelectronic device using digital signal processing to calculate temperature and deformation values along optical fibers, featuring a reduced component count, low-voltage operation, and digital processing of signals via FFT algorithms, eliminating the need for bulky analog components and prior checks, allowing for portable and autonomous operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If analog heterodyne detection with a Brillouin ring laser is used, then frequency transposition to lower frequency is achieved, but device complexity and power consumption increase significantly
Solution Approach 1:
The patent replaces the complex analog heterodyne detection system with a digital signal processing approach. Instead of using a Brillouin ring laser and analog mixing, the system uses a simple photodetector to detect the backscattered signal directly and then applies digital FFT processing to analyze the Brillouin frequency shift. This substitution of analog mechanical/optical systems with digital processing reduces device complexity while maintaining the frequency transposition capability.
Solution Approach 2:
The patent changes the detection approach from analog frequency mixing to digital frequency analysis. By using a photodetector to convert optical signals to electrical signals and then applying digital FFT processing, the system achieves frequency transposition through parameter transformation in the digital domain rather than through analog optical mixing, thereby reducing device complexity.
2Difficulty of detecting and measuring
If analog heterodyne detection with a Brillouin ring laser is used, then frequency transposition to lower frequency is achieved, but power consumption increases
Solution Approach 1:
The patent replaces the power-intensive analog heterodyne detection system with a low-power digital signal processing approach. The analog system requiring a Brillouin ring laser and active optical components is substituted with a simple photodetector and digital FFT processing, significantly reducing power consumption while maintaining the frequency analysis capability.
Solution Approach 2:
The system uses the backscattered light signal itself as the input for digital processing, eliminating the need for separate local oscillator lasers and analog mixing components. The digital FFT algorithm processes the signal directly, making the system self-sufficient and low-power consuming.
3Length of stationary object
If OTDR technique with light pulse propagation is used, then distributed measurement over tens of kilometers is achieved, but measurement time increases
Solution Approach 1:
The patent uses periodic pulse transmission through the optical fiber and applies FFT processing to the backscattered signals. By transmitting pulses at regular intervals and using spectral analysis, the system achieves rapid measurement of distributed parameters along the fiber length without requiring excessively long measurement times, thus resolving the contradiction between measurement range and measurement time.
4Device complexity
If a simple photodetector with digital processing is used, then device complexity and power consumption are reduced, but frequency resolution may be compromised
Solution Approach 1:
The patent transforms the frequency analysis from an analog domain to a digital domain using FFT processing. By changing the parameter space from analog voltage frequencies to digital frequency bins through spectral analysis, the system achieves high frequency resolution with simple photodetector hardware, resolving the contradiction between device simplicity and measurement precision.
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 device achieves rapid measurement times (seconds for 10 km fibers) with improved spatial resolution and energy efficiency, enabling continuous monitoring of civil engineering structures with reduced maintenance costs and early detection of structural disorders.
Implementation Method 1
a frequency-shifted pulse generator device (30) comprising at least one acousto-optic modulator (3) capable of transforming said continuous signal into a pulsed signal
Implementation Method 2
injected into an optical fiber (5) to be tested so that it emits in return a signal by spontaneous Brillouin backscattering
Implementation Method 3
said reference optical fiber (18) emitting a signal by spontaneous Brillouin backscattering, in response to said continuous light signal emitted in said second arm by said light source (1)
Implementation Method 4
a detection module (9) capable of detecting said beat between said backscattered signal from said optical fiber (5) under test and said backscattered signal from said reference optical fiber (18)
Data Source
Figure 1
Figure 2~3A
Figure 3B~3C
AI summary
The invention relates to a method for digitally processing a signal generated by an optoelectronic distributed measuring device based on Brillouin scattering, said device comprising: a continuous-wave light source (1); a coupler (2); an acousto-optical modulator (3); an optical fibre (5) to be tested so that it emits in response a signal by spontaneous Brillouin backscatter at a frequency vF equal to vp - vBz, where vBz is the Brillouin frequency to be measured at every point z of said optical fibre (5); a local oscillator (16) emitting another light signal intended to be mixed with said response signal emitted by Brillouin backscatter by said optical fibre (5) to be tested; a detecting module (9) able to detect said Brillouin frequency shift vBz at every point z of said optical fibre; and a processing module allowing this Brillouin frequency shift vBz to be linked at every point z of said optical fibre to a temperature or a deformation value. The local oscillator (16) comprises a reference optical fibre (18) having a Brillouin frequency identical or close to that of the optical fibre (5) to be tested, said reference optical fibre (18) emitting a signal by spontaneous Brillouin backscatter, in response to the continuous-wave light signal emitted by said light source (1), said Brillouin backscatter signal being emitted at a frequency VOL = vO - vBRef, where VBRef is the Brillouin frequency of the reference fibre without deformation and at a reference temperature. According to the invention, a signal corresponding to the beat between the backscattered signal generated by the optical fibre (5) to be tested and a backscattered signal generated by the reference optical fibre (18) is digitised and the digitised signal is sliced into a plurality of slices by applying a rectangular, or Hamming, or Hann, or Blackman-Harris, moving window, each slice having a width, equal to the temporal width of a half-pulse of the pulsed signal injected into the optical fibre (5) to be tested, centred on a time t corresponding to a point of coordinate z of said optical fibre (5) to be tested.