Optical Path Length Modulator for DTS Noise Reduction
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Solution Overview
Problem
Distributed temperature sensing systems in the drilling and completion industry face systematic noise issues in optical fibers, which affect the accuracy of temperature determination and loss estimation.
Innovation Solution
The use of a multimode optical fiber and an optical path length modulator to excite different propagation modes, reducing noise levels by averaging down systematic noise and improving the signal-to-noise ratio through modulation of the optical path length during light pulse transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-mode optical fiber is used for DTS, then the fiber structure is simple and easy to manufacture, but systematic noise occurs due to multiple propagation modes causing inaccurate temperature determination
Solution Approach 1:
The patent applies the dynamics principle by dynamically switching between single-mode and multimode operation of the optical fiber using an optical path length modulator. The fiber transitions from a static single-mode configuration to a dynamic multimode configuration during measurement, allowing the system to exploit multiple propagation modes for noise reduction while maintaining manufacturing simplicity. This dynamic switching enables the fiber to adapt its mode structure based on measurement requirements.
Solution Approach 2:
The patent implements parameter changes by modifying the optical path length of the fiber using an optical path length modulator. By changing the physical length parameter of the fiber path, the system induces mode coupling between different propagation modes. This parameter change transforms the fiber's modal characteristics, enabling the excitation and mixing of multiple modes to average out systematic noise and improve temperature measurement accuracy.
2Measurement precision
If optical path length modulation is applied to excite different propagation modes, then noise levels are reduced and signal-to-noise ratio improves, but the device complexity increases due to additional modulator components
Solution Approach 1:
The optical path length modulator serves multiple functions simultaneously: it modulates the optical path length to excite different propagation modes, couples between modes to average systematic noise, and enables the fiber to operate in both single-mode and multimode regimes. This multi-functionality justifies the added component complexity by providing several measurement capabilities from a single device element.
Solution Approach 2:
The patent converts the potentially harmful effect of mode-related systematic noise into a beneficial effect by using optical path length modulation to deliberately excite and mix multiple propagation modes. The noise that would normally degrade measurement accuracy is transformed into a useful signal averaging mechanism, where the interference patterns from multiple modes cancel out systematic errors and improve the signal-to-noise ratio.
3Measurement precision
If multiple propagation modes are excited in the optical fiber, then systematic noise is averaged down and temperature measurement accuracy improves, but the optical fiber must support complex multimode operation
Solution Approach 1:
The optical path length modulator applies periodic modulation to the fiber's optical path length, creating time-varying conditions that systematically excite different propagation modes. This periodic action ensures that all relevant modes are sampled and averaged over time, maximizing the noise reduction effect while maintaining a simple modulation scheme that does not require complex fiber designs.
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 results in more accurate temperature determination by smoothing out Rayleigh traces and approximating the true loss curve of the optical fiber, leading to lower noise and more precise temperature measurements.
Implementation Method 1
an optical fiber to propagate the light pulses
Implementation Method 2
an optical path length modulator to modulate the optical path length of the optical fiber as the light pulses are transmitted into the optical fiber
Implementation Method 3
At least two photodetectors detect backscatter reflected in the optical fiber
Implementation Method 4
DTS involves estimating temperature based on different wavelengths of light scattered by an optical fiber
Data Source
AI summary
A system and method to determine temperature include an optical fiber and at least two pulse laser sources to transmit light pulses with at least two wavelengths into the optical fiber. The system also includes an optical path length modulator to modulate the optical path length of the optical fiber as the light pulses are transmitted into the optical fiber. At least two photodetectors detect backscatter reflected in the optical fiber, and a processor determines the temperature based on the backscatter.