Spectral Image Pickup Optics for FFT-Based Thickness Measurement
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Solution Overview
Problem
Existing methods for calculating the thickness of a test object using spectral imaging face challenges due to irregular sampling intervals in wavenumber direction, leading to long processing times and reduced measurement accuracy, as they require additional resampling and cannot utilize fast Fourier transform effectively.
Innovation Solution
An image pickup apparatus with a spectral optical system that divides light into multiple wavelengths and condenses them on an image sensor, ensuring regular pixel spacing by satisfying specific inequalities, allowing for efficient Fourier transform processing and accurate thickness measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wavenumber transform processing is performed to calculate thickness from spectral waveform, then thickness measurement can be achieved, but the sampling intervals in wavenumber direction become irregular requiring additional resampling processing which increases overall processing time
Solution Approach 1:
The patent applies preliminary action by pre-designing the optical system with specific optical path length relationships that ensure regular sampling intervals in wavenumber space before measurement begins. The optical path lengths are configured in advance to satisfy specific mathematical relationships, eliminating the need for post-measurement resampling operations.
Solution Approach 2:
The patent replaces the conventional mechanical/resampling-based approach to achieve regular sampling with an optical system design based on precise optical path length control. By using optical interference and path length relationships, the system achieves regular wavenumber sampling directly during measurement without requiring subsequent digital resampling processing.
2Productivity
If resampling processing is performed to make sampling intervals regular for FFT, then fast Fourier transform can be used, but additional processing steps are required which reduces measurement accuracy
Solution Approach 1:
The optical system is designed in advance with optical path lengths that satisfy specific mathematical relationships to ensure that spectral components are sampled at regular intervals in wavenumber space. This preliminary configuration eliminates the need for resampling operations that would otherwise be required to enable FFT processing.
Solution Approach 2:
The patent changes the optical path length parameters of the interferometer arms to specific values that satisfy mathematical relationships ensuring regular wavenumber sampling. By adjusting these physical parameters during system design and calibration, the system achieves optimal sampling conditions directly during measurement.
3Measurement precision
If Lomb-Scargle method is used to obtain power spectrum with irregular sampling intervals, then measurement can proceed without resampling, but processing time is longer than FFT
Solution Approach 1:
The system performs preliminary configuration of optical path lengths to ensure regular sampling intervals in wavenumber space before measurement begins. This pre-configuration enables the use of efficient FFT algorithms during actual measurement and processing, avoiding the need for slower Lomb-Scargle methods.
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 regular sampling intervals in wavenumber space, facilitating fast Fourier transform and improving measurement accuracy and efficiency in spectral imaging.
Implementation Method 1
an optical system configured to divide light from an area extending in a first direction of an object into a plurality of lights in a section orthogonal to the first direction, and to condense the plurality of lights on an imaging surface of the image sensor
Implementation Method 2
divide light from an area extending in a first direction of an object into a plurality of lights in a section orthogonal to the first direction, and to condense the plurality of lights on an imaging surface of the image sensor
Data Source
AI summary
An image pickup apparatus includes an image sensor, and an optical system configured to divide light from an area extending in a first direction of an object into a plurality of lights in a section orthogonal to the first direction, and to condense the plurality of lights on an imaging surface of the image sensor. A predetermined condition is satisfied.