Fabry-Perot Sensor Gap Tracking Algorithm
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Solution Overview
Problem
Existing signal processing algorithms for Fabry-Perot sensors are not robust enough to accurately measure gaps when the sensor and wedge interferometer gaps are made of different materials, leading to errors due to changes in refractive index, resulting in inaccurate and discontinuous gap measurements.
Innovation Solution
A new algorithm that identifies and tracks a unique feature across the entire range of gaps in the correlation burst waveform, using the relationships between features to select and compute the gap without discontinuous jumps, by analyzing the cross-correlation pattern between a Fabry-Perot sensor with an air gap and a Fizeau wedge with a transparent oxide gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a simplistic algorithm is used to identify the largest magnitude peak or valley in the correlation burst waveform, then the algorithm is easy to implement, but measurement precision deteriorates when the Fabry-Perot gap and wedge interferometer gap are made of different materials due to refractive index differences causing burst shape evolution
Solution Approach 1:
The algorithm performs preliminary identification of the dominant peak or valley in the correlation burst waveform before tracking. By pre-identifying which feature (peak or valley) is dominant at the current gap position, the algorithm establishes a reference point for subsequent tracking operations, ensuring consistent feature selection throughout the measurement range
Solution Approach 2:
The algorithm continuously monitors the correlation burst waveform and adjusts feature tracking based on feedback from the dominant peak/valley identification. When the dominant feature changes or when tracking discrepancies occur, the algorithm uses the identified dominant feature as feedback to correct and maintain accurate gap measurements across varying refractive index conditions
2Measurement precision
If feature tracking is performed across the entire range of gaps, then measurement precision is improved with no discontinuous jumps, but device complexity increases due to the sophisticated signal-processing algorithm required
Solution Approach 1:
The algorithm uses the inherent characteristics of the correlation burst waveform itself to guide the tracking process. By identifying the dominant peak or valley and following its evolution across the gap range, the algorithm allows the signal's own structure to drive the measurement process, reducing the need for external complex processing while maintaining continuity and accuracy
Solution Approach 2:
The algorithm dynamically adapts to changes in the correlation burst waveform parameters as the gap varies. By monitoring how the dominant peak or valley position and characteristics change with gap distance, the algorithm maintains accurate tracking throughout the entire measurement range without requiring fixed processing complexity
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 provides accurate and repeatable gap measurements across the full range of gaps, reducing errors associated with evolving burst waveforms and improving the dynamic range and resolution of the system.
Implementation Method 1
The light reflected from the two surfaces (i.e., that which is transmitted back into fiber 10 via surfaces 12a and 12b) interferes to create an interference pattern, also called a modulation pattern.
Implementation Method 2
The correlation pattern is read out by a linear array of photodetector elements also referred to as pixels.
Data Source
AI summary
An algorithm and method for calculating an interferometric gap is disclosed that comprises providing an interferometric sensor having a first gap and an interferometric correlation element having a second gap placed in series with the first gap. A correlation burst waveform is generated having a plurality of features wherein the shape of the burst waveform evolves across the range of the second gap. Means are provided for tracking the features across the entire range of gaps and determining the dominant peak or dominant valley to determine the first gap.