Optical Interference Measurement for Precise Wedge Angles
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Solution Overview
Problem
Existing optical measurement techniques, such as those using wedged cells, are limited by the precision of angle measurement, which affects the accuracy of determining refractive indices and surface roughness.
Innovation Solution
A method involving illuminating light on an object with intersecting surfaces, capturing interference patterns, and using Fourier transforms to determine angles and refractive indices, and a system comprising an optical system, sensor, and computing system to analyze these patterns for precise measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional angle measurement methods are used to measure wedge cell angles, then the measurement process is simple, but the measurement precision is limited
Solution Approach 1:
The patent replaces traditional mechanical angle measurement methods with optical interference measurement. By using laser illumination and capturing interference fringes between light reflected from the front and back surfaces of the wedge cell, the system achieves sub-arcsecond precision without mechanical contact or alignment, thus improving measurement precision while maintaining operational simplicity.
Solution Approach 2:
The patent introduces an optical intermediary (the interference pattern) to measure the angle. Instead of directly measuring the physical angle with mechanical instruments, the system uses the interference fringe spacing as an intermediary parameter that can be measured with high precision using a camera and processed through Fourier transform to derive the wedge angle.
2Measurement precision
If Fourier transform method is used to analyze interference patterns, then measurement precision is improved, but computational complexity increases
Solution Approach 1:
The patent replaces complex iterative computational methods with a direct Fourier transform approach. By transforming the spatial domain interference pattern into the frequency domain, the system can directly extract the wedge angle and refractive index information from the spectral peaks, significantly reducing computational complexity while maintaining high precision measurement of refractive indices.
3Measurement precision
If multiple measurements are taken to improve accuracy, then measurement precision increases, but measurement time increases
Solution Approach 1:
The patent transitions from point-by-point or line-by-line surface scanning to full-field parallel measurement. By capturing the entire interference pattern across the surface in a single shot using a camera, the system measures all surface height information simultaneously in the spatial domain, then processes the complete surface profile through Fourier transform to extract roughness parameters, achieving high precision measurement of surface roughness without sequential scanning and thus eliminating the time penalty associated with multiple 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
Enables precise measurement of angles and refractive indices, and surface profiling of uneven surfaces, improving the accuracy of optical measurements.
Implementation Method 1
a first light beam reflected from the first surface and a second light beam reflected from the second surface
Implementation Method 2
capturing an interference pattern between a first light beam reflected from the first surface and a second light beam reflected from the second surface
Data Source
AI summary
Methods, apparatus, devices, subsystems, and systems for optical measurements are provided, e.g., precise measurement of a geometry of an element such as an angle of an object, a refractive index of a substance, or surface roughness of an uneven surface. In one aspect, a method includes: illuminating light on an object having a first surface extending along a first direction and a second surface extending along a second direction different from the first direction, capturing an interference pattern between a first light beam reflected from the first surface and a second light beam reflected from the second surface, and determining an angle between the first direction and the second direction based on a result of Fourier transform of the captured interference pattern.