Optical Strain Measurement with Cascaded Amplifiers for Phase Range Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing systems for position-dependent strain measurement in optical sensing fibers face challenges in obtaining phase measurements for all positions along the fiber due to low Rayleigh backscattering intensities, which often fall outside the usable optical intensity range.
Innovation Solution
A system utilizing a series arrangement of an optically pumped optical fiber amplifier and an electrically pumped semi-conductor optical amplifier, or a non-linear optical absorber, to ensure that coherent combinations of Rayleigh backscattering intensities are within a usable range for an electronic phase measuring subsystem.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a single optically pumped optical fiber amplifier is used to amplify backscattered light, then the gain can be increased to improve signal intensity, but the intensity range becomes uncontrolled causing measurements to fall outside the usable optical intensity range
Solution Approach 1:
The single amplifier is divided into two cascaded amplifiers: a first optically pumped optical fiber amplifier and a second electrically pumped semiconductor optical amplifier. This segmentation allows independent control of gain in each stage, enabling the system to cover a broader intensity range while keeping the output within the usable range for phase measurements.
Solution Approach 2:
The system dynamically adjusts the gain of each amplifier stage based on the required output intensity. The control circuit modifies the pump power to the first amplifier and the bias current to the second amplifier in real-time, enabling adaptive coverage of the usable intensity range for different fiber positions and conditions.
2Measurement precision
If high sampling frequency is used to achieve high spatial resolution, then the spatial resolution improves, but the low Rayleigh scattering intensity makes phase measurements difficult for positions outside the usable intensity range
Solution Approach 1:
The system changes the intensity parameter of the backscattered light by using cascaded amplification with controllable gain. This allows the intensity to be adjusted to fall within the usable range for the electronic phase measuring subsystem, enabling reliable phase measurements even at high sampling frequencies required for high spatial resolution.
3Illumination intensity
If the gain of the fiber amplifier is increased to raise the intensity envelope, then the intensity at distant fiber positions improves, but the intensity at other positions may exceed the usable optical intensity range
Solution Approach 1:
By segmenting the amplification into two stages with different characteristics, the system can distribute the total gain across both amplifiers. The first amplifier provides high gain for distant positions while the second amplifier with lower noise figure and controllable gain ensures the final output remains within the usable intensity range for all positions.
Solution Approach 2:
The control circuit uses feedback to monitor the output intensity from the second amplifier and dynamically adjusts the pump power and bias current to maintain the intensity within the usable range, preventing both under-amplification of distant positions and over-amplification of closer positions.
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 allows for reliable phase measurements at a wider range of intensities, reducing the number of positions along the fiber where no reliable phase measurements are possible, and enhancing the spatial resolution of strain measurements.
Implementation Method 1
an optically pumped optical fiber amplifier (14) to amplify light returned from within the optical sensing fiber (12) through the first end
Implementation Method 2
an electrically pumped semi-conductor optical amplifier (16) coupled to an output of the optically pumped optical fiber amplifier (14)
Implementation Method 3
or a non-linear optical absorber up-front from the splitting of the optical paths
Implementation Method 4
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 5
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
Data Source
Figure 1
Figure 1a
Figure 2
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.