Interferometric Encoder Spectral Analysis for Refractive Index Errors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optical interferometry systems face measurement errors due to refractive index fluctuations in air, particularly when the test light beam travels long distances, leading to inaccuracies in displacement measurements.
Innovation Solution
The use of wavelength-swept or broadband light beams in optical encoder configurations, where the interference patterns resulting from interaction with an encoder scale are analyzed as a function of wavelength to determine the position and motion of the encoder scale, allowing for reduced measurement errors and increased precision by minimizing the impact of atmospheric fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the test light beam travels long distances in air for displacement measurement, then the measurement range is increased, but the measurement precision deteriorates due to refractive index fluctuations
Solution Approach 1:
The patent changes the spectral parameters of the light source from monochromatic to broadband, enabling interferometric measurements with reduced sensitivity to atmospheric refractive index fluctuations. The broadband light source allows spectral analysis that can distinguish between path length changes and refractive index changes, thereby maintaining measurement precision over long beam paths.
2Device complexity
If traditional monochromatic laser interferometry is used, then the measurement system is simple, but the measurement accuracy deteriorates in long air paths due to atmospheric effects
Solution Approach 1:
The patent modifies the spectral parameter of the light source from monochromatic to broadband, which enables the system to perform spectral analysis that is less sensitive to atmospheric refractive index fluctuations. This parameter change maintains relatively simple interferometer structure while significantly improving measurement accuracy in long air paths.
3Measurement precision
If broadband light beams are used for interferometric measurement, then the precision is improved by minimizing atmospheric fluctuations, but the device complexity increases
Solution Approach 1:
The patent implements parameter changes in the light source (to broadband) and applies spectral analysis techniques that, while increasing some system complexity, provide significantly improved measurement precision by minimizing the impact of atmospheric fluctuations on the interferometric measurements.
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 precise displacement measurements with reduced errors by analyzing interference patterns across different wavelengths, providing accurate information about the encoder scale's position and motion, including multiple degrees of freedom, while minimizing the influence of air path variations.
Implementation Method 1
An interference beam resulting from an interference of the wavelength-swept beam or the broadband beam subsequent to interaction with the encoder scale and at least one other beam is recorded and analyzed
Implementation Method 2
The encoder head directs a test beam to the encoder scale, where it diffracts
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Determining information about a degree of freedom of rigid body motion of an encoder scale includes: directing a first beam toward an encoder scale, in which the first beam diffracts from an encoder scale; combining a diffracted component of the first beam with a second beam to form an interfering output beam; monitoring changes in the output beam as a function of a wavelength of the first and second beams,; and determining the information about a degree of freedom of rigid body motion of the encoder scale based on changes in the output beam as a function of the wavelength.