System and method for monitoring Fabry-Pérot cavity displacements
Inventors
Sweeney, Daniel C. • Birri, Anthony • Petrie, Christian M.
Assignees
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Publication Number
US-12467813-B2
Publication Date
2025-11-11
Expiration Date
Abstract
A system and method for monitoring Fabry-Perot cavity (“FPC”) displacement implementing a predictor-corrector scheme. The system includes an optical interrogator apparatus and a data processing apparatus. The optical interrogator apparatus interrogates the FPC, obtains a spectral interference pattern and outputs a corresponding signal including data associated with a plurality of peaks. The data processing apparatus processes the output signal to produce a prediction for a peak location based on the data associated with the plurality of peaks, and then uses the prediction to identify as correct one of the plurality of peaks. The data processing apparatus then determines and outputs a plurality of FPC length variations. In one embodiment, the data processing system implements a period tracking algorithm to produce the prediction based on the data associated with the plurality of peaks, and uses a phase tracking algorithm to determine an FPC length variation using the identified peak.
Core Innovation
A system interrogates a Fabry-Perot cavity with light to produce a periodic spectral interference pattern whose peak locations vary in time in accordance with variations of the Fabry-Perot cavity length. The optical interrogator apparatus spans an operational spectral range and outputs a signal of the peak locations, and the data processing apparatus receives the peak-location signal and determines FPC length variations as a function of time.
The data processing apparatus determines a reference length of the Fabry-Perot cavity and, for each instance following the reference instance, determines a current length based on the signal of the peak locations. Using the current length, the reference length, and the reference instance of the signal, the data processing apparatus predicts peak locations corresponding to the current instance and identifies corrected peak locations as the peak locations within the operational spectral range nearest to the predicted peak locations.
The data processing apparatus estimates a current FPC length variation based on the corrected peak locations and reference information, and determines the current FPC length variation as a median of previously estimated FPC length variations over a moving time window of predetermined duration. The method and system further use a period tracking algorithm to produce a prediction for a peak location and a phase tracking algorithm to estimate a plurality of FPC length variations, and output a signal of the determined FPC length variations.
Claims Coverage
The document includes three independent claims, with inventive features centered on interrogating an FPC to output time-varying peak-location data from a periodic spectral interference pattern, and hybrid predictor-corrector processing combining reference-based peak prediction with corrected peak selection and phase-tracking-based median aggregation.
Peak-location signal from a periodic spectral interference pattern over an operational spectral range
interrogate the FPC with light; produce a periodic spectral interference pattern over an operational spectral range; locations of peaks vary in time with variations of the FPC length; output a signal of the peak locations.
Reference length determination and current length determination from peak locations
determine a reference length of the FPC from a reference instance of the signal of the peak locations; determine a current length of the FPC from a current instance of the signal of the peak locations.
Predict peak locations and select corrected nearest peaks within the operational spectral range
predict peak locations corresponding to the current instance based on the current length, the reference length, and the reference instance of the signal of the peak locations; identify as corrected peak locations the peak locations of the current instance within the operational spectral range that are nearest to the predicted peak locations.
Median-based estimation and moving time-window aggregation of FPC length variations
estimate a current FPC length variation based on the corrected peak locations and reference information; determine the current FPC length variation as a median of previously estimated FPC length variations over a moving time window of predetermined duration; output a signal of the determined FPC length variations.
Statistical analysis for reference/current length, variation estimation, and output of FPC length variations
determine a reference length of the FPC as a function of FPC lengths corresponding to a reference instance of the signal of the peak locations; determine a current length of the FPC as a statistical analysis of FPC lengths corresponding to a current instance of the signal of the peak locations; estimate a current FPC length variation as a statistical analysis of FPC length variations corresponding to the corrected peak locations, the reference instance of the signal of the peak locations, and the reference length; output a signal of the FPC length variations.
Method of monitoring using period tracking prediction and phase tracking variation estimation
interrogating the FPC with light over an operational spectral range; obtaining a spectral interference pattern representative of light returning from the FPC; producing a signal including data associated with a plurality of peaks; determining a reference length of the FPC as a function of FPC lengths corresponding to a reference instance of the signal; processing the signal using a period tracking algorithm to produce a prediction for a peak location; identifying as correct one of the plurality of peaks closest to the predicted peak location; estimating a plurality of FPC length variations using a phase tracking algorithm; determining the current FPC length variation as a median of previously estimated FPC length variations over a moving time window of predetermined duration; outputting a signal of the determined FPC length variations.
Across the independent claims, the core inventive coverage is a measurement system and method that outputs peak-location data from a periodic spectral interference pattern over an operational spectral range, uses reference/current length information to predict peak locations and select corrected nearest peaks, and derives FPC length variations via phase tracking with median-based estimation and moving time-window aggregation.
Stated Advantages
Improved precision for measured FPC length variations, including nanometer-level precision and up to ~100× better than filtered period tracking.
Improved ability to measure larger deflections, including larger deflections greater than 20 μm.
Documented Applications
Measuring corrosion monitoring in nuclear reactors.
Pressure sensing.
Ultrasonic additive manufacturing with an embedded fiber in a metal matrix.
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