Optical Interrogator Wavelength Sweeping for Distributed Fiber Sensing
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Solution Overview
Problem
Distributed optical fiber sensing systems face complications such as signal distortions and poor signal-to-noise ratio due to non-linear effects like self-phase modulation, cross-phase modulation, and four-wave mixing in amplified multi-span optical fiber lines, which limit the sensing reach and accuracy.
Innovation Solution
The system employs an optical interrogator that transmits optical probe signals in multiple non-overlapping wavelength channels with varying center wavelengths, using a repeat period where the wavelength increases or decreases, and includes load light to stabilize optical amplifiers, thereby managing transient behavior and reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If optical probe signals are transmitted through amplified multi-span optical fiber lines, then sensing reach is extended, but signal distortions occur due to non-linear effects
Solution Approach 1:
The optical fiber line is divided into multiple spans with optical amplifiers placed at intervals. Each span is interrogated separately with probe signals, allowing the system to extend sensing reach through multiple amplified sections while managing non-linear effects by limiting the length of individual spans.
Solution Approach 2:
The system uses periodic transmission of probe signals with a defined repeat period, cycling through multiple wavelength channels in a systematic sequence. This periodic interrogation allows optical amplifiers to stabilize between measurements, reducing transient behavior and non-linear distortions while maintaining extended sensing capability.
2Adaptability or versatility
If multiple wavelength channels are used to extend sensing capability, then measurement coverage is improved, but wavelength switching causes transient behavior in optical amplifiers
Solution Approach 1:
The system implements a smooth wavelength sweeping sequence where the center wavelength is gradually changed from longer to shorter wavelengths over at least one-quarter of the repeat period, rather than abrupt switching. This preliminary smoothing action prevents sudden transient behavior in optical amplifiers while maintaining multi-wavelength measurement coverage.
Solution Approach 2:
The optical transmitter dynamically adjusts the center wavelength of probe signals in a controlled manner, sweeping through wavelength channels systematically. This dynamic wavelength adjustment allows the system to access multiple measurement channels while adapting the transmission characteristics to minimize amplifier transients.
3Measurement precision
If optical probe signals are transmitted at high power to improve signal-to-noise ratio, then sensing accuracy is improved, but non-linear effects like self-phase modulation increase
Solution Approach 1:
The system combines multiple wavelength channels to interrogate the optical fiber, where each channel carries probe signals at optimized power levels. By merging the information from multiple channels, the system achieves improved signal-to-noise ratio and sensing accuracy without requiring excessive power in any single channel, thus reducing non-linear effects.
Solution Approach 2:
The system changes the wavelength parameter of probe signals across multiple channels, allowing each wavelength to be transmitted at appropriate power levels that balance signal-to-noise ratio with non-linear effect mitigation. This parameter variation enables accurate sensing while avoiding the harmful effects of high single-channel power.
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 mitigates signal distortions and improves the signal-to-noise ratio, extending the sensing reach and accuracy of distributed optical fiber sensing systems by stabilizing optical amplifiers and minimizing non-linear effects.
Implementation Method 1
an optical transmitter and an optical receiver. The optical transmitter is configured to transmit optical probe signals
Implementation Method 2
The optical receiver is configured to receive back scattered light from the optical probe signals
Implementation Method 3
The optical receiver is configured to receive back scattered light from the optical probe signals and to obtain sensing information therefrom
Data Source
Figure 1
Figure 2
Figure 3A~3D
AI summary
An optical interrogator for a distributed fiber optic sensor includes an optical transmitter and an optical receiver. The optical transmitter is configured to transmit optical probe signals at a temporal series of corresponding start times, such that center wavelengths of different ones of the optical probe signals transmitted within a repeat period are different. The optical receiver is configured to receive back scattered light from the optical probe signals and to obtain sensing information therefrom. In some implementation, the optical transmitter may increase the center wavelength of the transmission over one part of a transmission repeat period, and decrease it over another part of the transmission repeat period.