Fabry-Perot Sensor Optical Path Length Measurement
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Solution Overview
Problem
Current fiber optic interferometric sensor systems for measuring parameters like pressure, temperature, and optical refractive indices are limited by high costs, complex production, and reduced accuracy due to the need for high-resolution spectrometers and precise optical wedges, which are expensive and resource-intensive, and require complex calibration and calculation methods.
Innovation Solution
A method using a Fabry-Perot sensor system with a white light source, optical waveguide, and spectrometer to directly determine the optical path length difference by converting the spectrometer signal into an interferogram with a cosine function, allowing for precise and economical measurement of optical path length differences without the need for complex algorithms or additional reference configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-resolution spectrometers with more than 3500 sensor elements are used, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies partial action by using only a subset of the spectrometer's sensor elements (e.g., 3648 pixels) to capture the interferogram. Instead of requiring all sensor elements to be actively used for measurement, the system processes only the necessary portion of the spectral data, thereby reducing the effective device complexity while maintaining measurement precision for optical path length differences.
2Measurement precision
If complex calibration and calculation methods are used, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The system implements self-service through automatic calibration and evaluation algorithms that perform complex calculations without requiring manual intervention. The evaluation unit automatically processes the interferogram data, applies necessary corrections, and determines the optical path length difference, making the system easy to operate while maintaining high measurement precision through sophisticated internal processing.
3Manufacturing precision
If precise optical wedges with reflection layers are used, then manufacturing precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent extracts the complex optical wedge component with reflection layers from the measurement system and replaces it with a simpler Fabry-Perot interferometer configuration. This eliminates the need for precisely manufactured optical wedges with multiple reflection layers, thereby improving ease of manufacture while maintaining or enhancing manufacturing precision through the alternative interferometric approach.
4Measurement precision
If high-quality spectrometers with better than 1 nm resolution are used, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent changes the operational parameters of the spectrometer by utilizing the full spectral range and all available sensor elements to capture the interferogram, rather than requiring high spectral resolution. The system processes the interferometric data through mathematical transformations (Fourier transform or correlation methods) to extract optical path length difference information, thereby achieving accurate measurements with lower-cost spectrometers that have coarser resolution but broader spectral coverage.
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 enables fast, precise, and cost-effective measurement of optical path length differences with reduced computational complexity and resource requirements, suitable for industrial applications and high-temperature, chemically aggressive environments, while maintaining high sensitivity and stability.
Implementation Method 1
difference of the optical path length of light reflected at the front face of the cavity and that which is reflected at the rear face of the cavity
Implementation Method 2
Typical representatives of such measuring systems are such which are based on Fabry-Perot (FP) sensors
Implementation Method 3
determining the optical spectrum of the reflected light in the spectrometer
Implementation Method 4
broadband or white light source with short coherence wavelength, such as, for example, an incandescent bulb or a white-light diode or Light Emitting Diode (LED)
Data Source
AI summary
For evaluation of a measured parameter with a measuring cell having a cavity which generates for light an optical path length difference changing corresponding to the variation of the measured parameter, the method includes: introducing light from a white light source with the aid of an optical waveguide via a coupler (3) disposed in the path of the optical waveguide into the cavity, coupling out at least a portion of the light reflected back into the optical waveguide from the cavity with the aid of the coupler and conducting this reflected light to an optical spectrometer, determining the optical spectrum of the reflected light in the spectrometer and generating a spectrometer signal, conducting the spectrometer signal to a computing unit, wherein the spectrometer signal is directly converted through the computing unit to an interferogram and from its intensity progression the location of the particular extremal amplitude value is determined and this particular location represents directly the particular value of the optical path length difference in the cavity, which comprises the measured parameter.