DAS Interferometer Phase-Shift Correction Under Variable Amplification
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Solution Overview
Problem
Existing optical interferometry systems face challenges in accurately determining phase shifts due to errors caused by variable optical amplification, which are not adequately addressed by existing methods like 3-way interferometry, leading to inaccuracies in phase difference measurements.
Innovation Solution
A method involving an optical interferometer system with multiple detectors and a phase modulator, where each detector output signal is corrected using an amplification-dependent correction based on average values or maximum and minimum signal values to compensate for intensity variations, allowing accurate phase shift computation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If variable optical amplification is applied to counteract intensity variation, then backscatter detectability is improved, but phase shift measurement accuracy deteriorates due to amplification errors
Solution Approach 1:
The system measures the actual amplification factor applied to the backscattered light and uses this feedback information to correct the phase shift measurements. The correction process compensates for errors introduced by variable optical amplification, allowing the system to maintain both improved detectability and accurate phase measurements.
Solution Approach 2:
The invention changes the parameter being measured from raw intensity values to corrected phase shift values that account for amplification variations. By deriving phase shift from intensity measurements and applying correction based on amplification factor, the system transforms the measurement process to eliminate the adverse effect of variable amplification.
2Reliability
If 3-way interferometry is used to achieve intensity-independent phase measurement, then robustness against intensity variation is improved, but measurement accuracy deteriorates due to amplification-induced errors
Solution Approach 1:
The system incorporates feedback by measuring the actual amplification factor and using it to correct phase shift calculations. This feedback mechanism allows 3-way interferometry to maintain its robustness against intensity variation while eliminating the accuracy degradation caused by variable amplification.
Solution Approach 2:
The invention creates a composite measurement approach that combines 3-way interferometry with amplification correction. By integrating multiple measurement strategies and correction mechanisms, the system achieves both the robustness of 3-way interferometry and the accuracy needed to compensate for amplification effects.
3Illumination intensity
If variable optical amplification is applied to equalize backscatter intensity, then signal detectability is improved, but phase shift determination accuracy worsens due to amplification variability
Solution Approach 1:
The system uses feedback by continuously monitoring the amplification factor applied to backscattered light and using this information to correct phase shift measurements. This allows the system to maintain uniform signal detectability while compensating for accuracy degradation.
Solution Approach 2:
The invention transforms the measurement parameter from direct intensity-based phase detection to corrected phase determination that accounts for amplification variability. By changing how phase shift is calculated and corrected, the system maintains intensity uniformity benefits while eliminating accuracy losses.
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
The method significantly reduces errors in phase shift measurements by compensating for intensity variations and amplification effects, enhancing the accuracy and robustness of phase shift determination in optical DAS systems.
Implementation Method 1
the phase difference between backscatter from different regions can be measured with high phase sensitivity from optical interferometric measurements
Implementation Method 2
a phase modulator coupled in series with the first interferometer arm
Implementation Method 3
applying variable optical amplification to the backscattered light so as to counteract intensity variation as a function of backscatter position in the optical fiber
Data Source
AI summary
An interferometer suitable for Distributed Acoustic Sensing (DAS) is has two interferometer arms of different length, from which light is fed to an N-way optical coupler (N at least 2). In DAS, the light is backscattered light received from within an optical fiber. Incoming light is amplified by an adjustable factor, which may vary as a function of time in DAS. The N way optical coupler supplies combinations of light from the arms with different relative phase offsets to each other to N outputs. Phase shift between interfering components is computed from the light intensities detected by detectors at the N outputs. Correction of the computed phase shift is applied dependent on the value of the adjustable amplification factor. For this, one interferometer arm comprises a phase modulator, which is used obtaining measured detector output signals from the detectors with different phase shifts by the phase modulator when the value of the adjustable factor is used. Data is determined that defines average of output signals of the different detectors under variation of different phase shift by the phase modulator based on the measured signals. For DAS, data defining time dependent averages according the variation of the factor are determined. A phase shift between interfering light is computed with a correction to compensate for differences between the average detector output signals for the individual optical detectors.