Distributed Optical Fibre Sensor Multi-Wavelength Vibration Detection
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Solution Overview
Problem
Distributed optical fibre sensors face limitations in detecting high-frequency vibrations due to the round-trip time constraint for light travel in long sensing fibres and non-linear response characteristics, which restrict the dynamic range and accuracy of vibration measurement.
Innovation Solution
The use of multiple probe light pulses of different wavelengths and durations, interleaved and simultaneously launched into the sensing fibre, allows for enhanced detection of acoustic vibrations by optimizing the response characteristics and phase biases, thereby extending the frequency range and achieving a more linear dynamic response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single probe light wavelength is used for interrogation, then the system is simple and easy to operate, but the maximum frequency of detection is limited by the round-trip time
Solution Approach 1:
The patent divides the single-wavelength interrogation into multiple wavelength channels, where each wavelength provides an independent measurement channel. This segmentation allows the system to effectively multiply the detection frequency capability by using parallel wavelength-based measurements, resolving the contradiction between system simplicity and detection frequency.
Solution Approach 2:
The patent introduces the wavelength dimension as an additional degree of freedom beyond the traditional time-domain measurement approach. By interrogating the sensing fibre with multiple wavelengths simultaneously or in sequence, the system transforms the single-dimensional time-based measurement into a multi-dimensional measurement space, thereby extending the detectable frequency range without increasing the round-trip time constraint.
2Speed
If probe light pulses of different wavelengths are launched simultaneously, then the detection frequency range is extended, but the device complexity increases due to multiple photodetectors and interleaving requirements
Solution Approach 1:
The patent designs a multi-wavelength probe light source that can generate and launch multiple wavelengths through a single integrated system. The same optical path and fibre sensing infrastructure are used for all wavelengths, making the system universal rather than requiring separate single-wavelength systems. This multi-functionality approach extends detection frequency while controlling the increase in device complexity.
Solution Approach 2:
The patent combines multiple wavelength channels into a unified measurement system where the backscattered light from different wavelengths is detected and processed together. By merging the measurement functions into a single integrated system with shared components, the patent reduces the overall complexity compared to having separate measurement systems for each wavelength.
3Area of stationary object
If the sensing fibre length is increased to cover larger areas, then the monitoring coverage is improved, but the round-trip time increases and limits the maximum frequency of response
Solution Approach 1:
The patent segments the monitoring task across multiple wavelength channels, where each wavelength independently monitors the entire fibre length. This segmentation allows the system to maintain high-frequency response capability even for long fibres, as the effective measurement rate is multiplied by the number of wavelength channels, thereby resolving the contradiction between monitoring coverage area and response frequency.
Solution Approach 2:
The patent uses the wavelength dimension to overcome the length constraint. By introducing multiple wavelengths as an additional degree of freedom, the system can effectively increase the measurement rate without physically shortening the fibre or reducing the monitoring coverage area. This dimensional approach allows long-fibre monitoring at high frequencies.
4Measurement precision
If multiple probe light pulses of different wavelengths and durations are used, then the dynamic range and linearity of response are improved, but the data processing complexity increases due to interleaving and analysis requirements
Solution Approach 1:
The patent performs preliminary organization of the measurement data by structuring the multiple wavelength and duration pulses in a systematic manner before analysis. The probe light source is configured to launch pulses in a predetermined sequence or pattern, and the detection system is pre-arranged to capture all wavelength channels simultaneously. This preliminary structuring simplifies the subsequent data processing and interleaving operations, thereby improving measurement precision while controlling processing complexity.
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 enables the detection of higher frequency vibrations and improves the dynamic range of the sensor by adjusting pulse durations and phase biases, resulting in a more accurate and linear measurement of acoustic vibrations along the sensing fibre.
Implementation Method 1
a measure of acoustic vibration is sensed as a function of position along a sensing optical fibre from the properties of probe light backscattered within the sensing fibre
Implementation Method 2
Such Rayleigh noise profiles arise from interference between the many components of the backscattered light originating from different points along a portion of the sensing optical fibre illuminated by the optical source
Implementation Method 3
detects variations in refractive index, induced by a physical forcing such as vibration, in the coherent Rayleigh noise profile
Data Source
Figure 1
Figure 2A~2D
Figure 2E~2H
AI summary
There is described a distributed optical fibre sensor for detecting one or more physical parameters indicative of an environmental influence on a sensor optical fibre, as a function of position along the sensor fibre. The sensor uses probe light pulses of different wavelengths. At least some of the probe light pulses may also be of different pulse lengths. The relative phase bias between interferometric signals in backscattered probe light of different wavelength pulses may also be controlled.