Optical Interferometric Measurement Sub-Nanometer Phase Detection
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Solution Overview
Problem
Conventional optical interferometric measurement apparatuses are unable to detect movements in sub-nanometer scales due to the resolution limitations of the point-spread-function, which spreads in the micrometer scale, and existing solutions that achieve sub-nanometer measurements are computationally intensive.
Innovation Solution
An optical interferometric measurement apparatus utilizing a wavelength-swept light source, an interference optical system, and a controller that calculates the departure of the sweep start frequency, converts it into a difference in sampling points, aligns the measurement data, and applies Fourier transform to determine the phase shift for precise sub-nanometer scale measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correlation calculation is performed between monitoring data and measurement data to achieve sub-nanometer measurement, then measurement precision is improved, but processing time increases significantly
Solution Approach 1:
The patent extracts only the essential information needed for phase measurement by calculating the departure of sweep start frequency from average value and converting it to sampling point differences. This selective extraction of critical parameters avoids the computationally intensive full correlation calculation while preserving measurement precision.
Solution Approach 2:
The patent performs preliminary alignment of measurement data by compensating for sampling point differences based on frequency departure calculations before applying Fourier transform. This preliminary correction of data misalignment eliminates the need for subsequent correlation calculations, achieving both high precision and fast processing.
2Device complexity
If conventional sampling method is used without frequency alignment, then processing is simpler, but measurement precision deteriorates due to phase errors
Solution Approach 1:
The patent replaces complex mechanical correlation-based alignment methods with a computational approach using Fourier transform and frequency departure calculation. This substitution maintains measurement precision while simplifying the overall processing framework.
Solution Approach 2:
The patent changes the parameter used for alignment from time-domain correlation to frequency-domain analysis by calculating sweep start frequency departure and its effect on sampling points. This parameter transformation enables precise phase measurement through a more efficient computational pathway.
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 high-speed measurement of object movement in the sub-nanometer scale by efficiently processing phase shifts, overcoming the limitations of existing technologies and achieving accurate nanometer-scale detection.
Implementation Method 1
a wavelength-swept light source
Implementation Method 2
an interference optical system adapted to output a monitoring interference signal and a measurement interference signal
Implementation Method 3
a Fourier transformation unit that applies Fourier transform to the measurement data in each period
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An optical interferometric measurement apparatus includes an interference optical system (2, 3) to output a monitoring interference signal S(t) and a measurement interference signal S(t) in accordance with light emitted from a wavelength-swept light source (1), and a controller (4) to measure a movement of an object to be measured (3k). The controller (4) has a storage (4b, 4b') to store monitoring data acquired by sampling the monitoring interference signal S(t) in each period T of the light source (1) and measurement data acquired by sampling the measurement interference signal S(t) in each period T of the light source (1) and Fourier transformation unit (4d) to apply Fourier transform to the measurement data. The controller (4) determines a phase ϕ of the measurement interference signal S(t) based on the Fourier-transformed measurement data and measures the movement of the object (3k) based on the phase.