Interferometric Sensor Interrogation System for Speed and Accuracy
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Solution Overview
Problem
Existing interferometric sensors, such as EFPI sensors, face challenges in achieving both high update rates and accurate absolute measurements, with single-wavelength systems providing only relative measurements and being prone to directional ambiguity and non-linear transfer functions.
Innovation Solution
A high-speed interrogation system utilizing a two-mode operation with a lower-speed, absolute measurement mode and a higher-speed, relative measurement mode, employing a fixed-wavelength and a tunable wavelength source to determine absolute optical path length changes, allowing for accurate and rapid sensor measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single-wavelength light source is used for high-speed interrogation, then update rate is improved, but measurement accuracy deteriorates due to directional ambiguity and non-linear transfer functions
Solution Approach 1:
The patent combines multiple light sources with different wavelengths (broadband source and narrowband sources) into a single interrogation system. This merging allows the system to simultaneously perform absolute measurements (using broadband source for unambiguous gap length) and relative measurements (using narrowband sources for high-speed tracking), thereby resolving the contradiction between speed and accuracy.
Solution Approach 2:
The system dynamically switches between different operational modes: using the broadband source for absolute measurement when accuracy is critical, and using narrowband sources for high-speed relative measurements when update rate is critical. This dynamic operation allows the system to adaptively optimize between speed and precision based on measurement requirements.
2Measurement precision
If a broadband light source is used for absolute measurements, then measurement accuracy is improved, but update rate deteriorates due to extensive processing requirements
Solution Approach 1:
The patent segments the measurement process into two distinct parts: absolute measurement (performed periodically using broadband source to establish reference) and relative measurement (performed continuously using narrowband sources). This segmentation allows the computationally intensive absolute measurement to be performed less frequently, while most measurements use the faster relative measurement method, thereby improving overall update rate while maintaining accuracy.
Solution Approach 2:
The system performs preliminary absolute measurement using the broadband source to establish a reference optical path length, then uses this reference for subsequent high-speed relative measurements. This preliminary action provides a foundation that enables faster subsequent measurements without sacrificing absolute accuracy.
3Speed
If amplitude-based interrogation is used for high-speed measurement, then update rate is improved, but measurement accuracy deteriorates due to directional ambiguity
Solution Approach 1:
The patent uses multiple wavelengths as intermediaries to resolve the directional ambiguity problem. By measuring interference patterns at multiple wavelengths simultaneously, the system can uniquely determine the gap length direction and magnitude, eliminating the ambiguity that plagues single-wavelength amplitude-based methods while maintaining high measurement speed.
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 system achieves greater measurement accuracy and speed by combining absolute and relative measurements, mitigating errors associated with simpler amplitude-based interrogation schemes and providing unambiguous gap length changes.
Implementation Method 1
The distance between R1 and R2 is same as the length of the gap and is one half of an optical path length. In an interferometric sense, R1 is the reference reflection, and R2 is the sensing reflection. These reflective signals interfere constructively or destructively based on wavelength and the optical path length difference between the reference and sensing fibers.
Implementation Method 2
Extrinsic Fabry Perot Interferometer (EFPI) sensors are based on the change in the optical length of a low-finesse Fabry-Perot cavity with respect to an applied measurand.
Data Source
AI summary
A high-speed interrogation system is provided for interferometric sensors, one example of which is an EFPI sensor, that operates based on spectral interference. The system uses a two mode operation that includes a lower speed, accurate absolute measurement mode and a higher speed, relative measurement mode. The system achieves greater overall measurement accuracy and speed than known sensor interrogation approaches.