DAS Selective Attenuator for Fiber-Optic Signal Loss
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Solution Overview
Problem
Current distributed acoustic sensing (DAS) technology in fiber-optic cables is limited by transmission losses and the inability to compensate these losses effectively, leading to restricted interrogation range and degraded performance in long repeatered systems, particularly due to high optical loss in High Loss Loopback fiber paths and limitations in sampling frequency.
Innovation Solution
The implementation of a DAS/Load selective attenuator in the optical propagation path, which allows for a differing load-to-DAS power ratio between the outbound and return fiber paths, optimizing the power distribution to reduce noise and nonlinear degradation, and using a DAS/Load Selective Attenuator to adjust the power ratio, ensuring higher load power in the return path compared to the outbound path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If traditional repeatered DAS systems use standard optical fiber paths, then the system can operate with conventional components, but the interrogation range is limited and sampling frequency is degraded due to high optical loss in HLLB fiber paths
Solution Approach 1:
The patent inverts the conventional HLLB architecture by implementing a low-loss loopback (LLLB) path where the loopback fiber has lower attenuation than the span fiber. This inversion allows the return signal to experience less loss, thereby extending the interrogation range and improving the signal-to-noise ratio at the interrogator.
Solution Approach 2:
The patent changes the attenuation parameter of the loopback fiber path to be lower than that of the span fiber. By selecting loopback fiber with optimized characteristics (lower loss), the system overcomes the limitation of high optical loss in traditional HLLB configurations and extends the maximum interrogation distance.
2Reliability
If load power is increased in the outbound path to compensate for losses, then signal level can be maintained, but nonlinear degradation and noise increase
Solution Approach 1:
The patent applies different power ratios of load to DAS signal in different parts of the system. In the outbound path, a lower load-to-DAS power ratio is used to minimize nonlinear effects, while in the return path, a higher load-to-DAS power ratio compensates for losses without requiring excessive outbound power. This local differentiation of power ratios optimizes both signal stability and noise performance.
Solution Approach 2:
The patent introduces an optical filtering circuit as an intermediary component that selectively passes the DAS signal while attenuating the load signal in the outbound direction, and vice versa in the return direction. This intermediary enables precise control of power ratios in each path, allowing the system to maintain signal levels without introducing harmful nonlinear effects.
3Measurement precision
If sampling frequency is increased to improve measurement resolution, then dynamic information quality improves, but the system performance degrades due to the round-trip time-of-flight limitation in long cables
Solution Approach 1:
The patent converts the harmful effect of long cable length (which causes large round-trip time and limits sampling frequency) into a benefit by using low-loss loopback fiber. The reduced optical loss allows higher signal power to be maintained over longer distances, enabling higher sampling frequencies to be used without degrading the signal-to-noise ratio, thus improving both measurement precision and sampling rate.
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 enhances system performance by reducing noise and nonlinear effects, thereby extending the interrogation range and improving the accuracy of strain measurements in long repeatered systems by maintaining a stable signal level and minimizing distortions.
Implementation Method 1
Through the phenomenon of Rayleigh backscattering (RBS), optical fibers within the fiber optic cable can serve as the sensing elements.
Data Source
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AI summary
A distributed fiber-optic sensing system transmits probe pulses and load light into a sequence of connected optical fiber segments. An optical receiver receives light from the probe pulses that has been backscattered in respective sensing fibers of the fiber segments and returned to the receiver over Rx fibers. Near the end of the sequence, an optical filtering circuit is connected to receive some of the load light output by the next-to-last optical fiber segment and to receive some of the light backscattered in the sensing fiber of the last optical fiber segment and to output at least some of the received load light and backscattered light into the Rx optical fiber respective to the sensing fiber of the last optical fiber segment. The optical filtering circuit is configured to output light with a lower ratio of powers than the light that is received by the optical filtering circuit, the ratio being the time-averaged optical power in a spectrum of the optical probe pulses over the time-averaged optical power in a spectrum of the load light.