Spectral Modulation for Instantaneous Phase-Shifting Interferometry
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Solution Overview
Problem
Conventional spectrally controlled interferometry requires complex manufacturing and precludes the use of common-path interferometers, limiting its advantages, and existing methods for obtaining multiple fringe patterns are not efficient for instantaneous phase-measurement systems.
Innovation Solution
Changing the mean wavelength of a spectrally controllable light source allows for multiple simultaneous phase-shifted correlograms to be produced, enabling instantaneous phase-shifting interferometry without altering the modulation period, using multiple beams with different mean wavelengths and conventional multiple-wavelength analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional spectrally controlled interferometry is implemented, then localized interference fringes can be produced, but the optical system becomes complex to manufacture and common-path interferometers cannot be used
Solution Approach 1:
The patent changes the spectral parameters of the light source (mean wavelength, bandwidth) to produce localized fringes in unbalanced-OPD interferometers, eliminating the need for complex balanced optical path designs while maintaining measurement precision
2Measurement precision
If multiple fringe patterns are obtained by changing modulation period or phase, then phase-shifting interferometry can be performed, but the system cannot achieve instantaneous phase measurement
Solution Approach 1:
The patent uses periodic modulation of the light source spectrum at different mean wavelengths to simultaneously generate multiple phase-shifted fringe patterns, enabling instantaneous phase measurement without temporal sequencing
Solution Approach 2:
By changing the mean wavelength parameter of the light source, the patent generates multiple correlograms simultaneously, each corresponding to a different phase shift, thus achieving instantaneous phase measurement
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 method enables efficient and accurate measurement of physical attributes by producing multiple phase-shifted correlograms simultaneously, improving the resolution and immunity to environmental disturbances in interferometric measurements.
Implementation Method 1
spectrally controlled interferometry is based on the idea of forming localized fringes at a predefined distance from the reference surface using an interferometer under unbalanced OPD conditions
Implementation Method 2
a change in the mean wavelength of the light produced by a spectrally controllable source, without further changes in the modality of modulation used to produce localized fringes, results in a change in the phase of the source's output
Data Source
AI summary
A light source capable of spectral modulation is modulated conventionally to produce a correlogram at the test surface position of an SCI interferometer. The mean wavelength of the light source is changed to obtain multiple corresponding phase-shifted correlograms that can be processed by applying conventional multiple-wavelength interferometric analysis to determine physical attributes of the test surface. One simple way to achieve this result is by splitting the light beam produced by the source into at least three simultaneous beams passed through filters with corresponding different mean-wavelength transmission bands. Because the correlograms are produced simultaneously, they can be used to practice instantaneous phase-shifting interferometry using conventional analysis algorithms.