Optical Strain Measurement with Amplified Rayleigh Phase Detection
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Solution Overview
Problem
Current systems for position-dependent strain measurement using Rayleigh backscattering in optical sensing fibers face challenges in achieving reliable phase measurements across all positions, particularly in long fibers, due to low scattering intensity and the need for significant amplification, which often results in intensities outside the usable range.
Innovation Solution
A system incorporating a series arrangement of optically pumped optical fiber amplifiers and electrically pumped semiconductor optical amplifiers or non-linear optical absorbers is used to ensure coherent combinations of Rayleigh backscattering intensities fall within a usable range for electronic phase measuring systems, allowing for wider intensity fluctuation detection and reducing the number of positions where reliable phase measurements are not possible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If optically pumped optical fiber amplifiers are used to amplify backscattered light, then the intensity of backscattered light is increased, but the intensity may rise above the usable optical intensity range
Solution Approach 1:
The patent employs dynamic gain control of the optical amplifier, adjusting the amplification factor in real-time based on the detected backscattered light intensity. This ensures that the amplified intensity remains within the usable range for phase measurements, preventing saturation while maintaining sufficient signal strength for reliable detection.
Solution Approach 2:
The system changes the amplification parameter of the optical amplifier adaptively. By monitoring the backscattered light intensity and adjusting the amplifier gain accordingly, the system optimizes the intensity level to fall within the usable range for interferometric phase measurements, resolving the contradiction between sufficient intensity and measurement reliability.
2Manufacturing precision
If high sampling frequency is used to enable high spatial resolution, then spatial resolution is improved, but the scattering Rayleigh intensity requirement becomes more demanding
Solution Approach 1:
The patent combines multiple technical approaches: using optically pumped optical fiber amplifiers to boost the weak Rayleigh backscattered signal, employing interferometric detection methods to extract phase information, and implementing dynamic gain control to optimize signal intensity. This combination enables high spatial resolution measurements without requiring excessively high inherent scattering intensity.
3Ease of manufacture
If commercially available optical communication fibers are used, then ease of manufacture is improved, but scattering Rayleigh intensity is reduced
Solution Approach 1:
The patent introduces an optically pumped optical fiber amplifier as an intermediary component between the sensing fiber and the detection system. This amplifier compensates for the low scattering intensity of commercially available communication fibers, enabling their use in distributed strain measurement applications without sacrificing measurement capability.
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 configuration enables reliable phase measurements at a larger number of positions along the optical sensing fiber by compressing higher intensity ranges relative to lower ones, ensuring that phase changes can be detected across a broader range of intensities, thereby improving the system's measurement capabilities.
Implementation Method 1
The amplification factor of the optical amplifier is set to bring an average of the backscattering intensity within a usable optical intensity range
Implementation Method 2
The optical phase difference between scattered light from pairs of different positions can be determined by feeding backscattered light from the optical sensing fiber along optical paths of different length and detecting interference between light from these different paths
Implementation Method 3
Rayleigh scattering is due to randomly distributed scatter centers in the optical sensing fiber. When a light pulse is transmitted into one end of the sensing fiber, distributed scattering of the pulse results in returned light at that end, with fluctuating phase and intensity as a function of time
Data Source
AI summary
A position dependent strain measurement system detected strain as a function of position in an optical sensing fiber using an interferometer having an input coupled to the first end of the optical sensing fiber. An electronic phase measuring sub-system is coupled to an output of the interferometer. The electronic phase measuring sub-system defines a usable optical intensity range of input light of the interferometer, wherein the electronic phase measuring sub-system is capable of measuring the phase of the input light. An optically pumped optical fiber amplifier is coupled between the first end of the optical sensing fiber and the input of the interferometer in series with an electrically pumped semi-conductor optical amplifier. The electrically pumped semi-conductor optical amplifier having a non-linear intensity amplification range that overlaps with the usable optical intensity range. The optically pumped optical fiber amplifier is configured to amplify an intensity of backscattered light from the optical sensing fiber into the non-linear intensity amplification range.