Phase Shifting Algorithm Sensitivity for Interferometry Errors
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Solution Overview
Problem
Sinusoidal phase-shifting interferometry in Fizeau interferometers is prone to signal distortions due to multiple reflections within the cavity, leading to errors in determining phase differences between reference and test light, which existing algorithms struggle to accurately mitigate.
Innovation Solution
Designing phase-shifting algorithms with specific sensitivity filters that reduce sensitivity to contributions from multiple reflections, particularly by enforcing peak sensitivity to the fundamental sinusoidal phase modulation amplitude while minimizing sensitivity to integer multiples, such as twice the amplitude, to suppress errors caused by multiple round-trip reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If sinusoidal phase-shifting interferometry is used in Fizeau interferometers, then the ease of operation and implementation is improved, but measurement precision deteriorates due to signal distortions from multiple reflections
Solution Approach 1:
The patent converts the harmful effect of multiple reflections into a beneficial filtering mechanism. By designing the phase-shifting algorithm to specifically suppress integer multiples of the fundamental frequency (including the second harmonic from double-pass reflections), the algorithm transforms what was previously a source of error into a means of identifying and eliminating spurious signals, thereby improving measurement precision while maintaining ease of operation
Solution Approach 2:
The patent modifies the algorithm's sensitivity parameters by enforcing peak sensitivity at the fundamental sinusoidal phase modulation amplitude while minimizing sensitivity to integer multiples. This parameter optimization allows the system to distinguish between valid interference signals and spurious reflections, resolving the precision issue without complicating the operational procedure
2Measurement precision
If algorithms with high sensitivity to fundamental phase modulation are used, then measurement precision is improved, but sensitivity to integer multiples (spurious reflections) increases
Solution Approach 1:
The patent applies local quality by creating non-uniform sensitivity distribution across different frequency components. The algorithm is designed with peak sensitivity specifically at the fundamental frequency while having minimal sensitivity at integer multiples. This localized sensitivity optimization allows the system to enhance detection of valid signals while simultaneously suppressing spurious reflections, resolving the contradiction between precision and harmful factor sensitivity
3Device complexity
If standard phase-shifting algorithms are used, then device complexity is kept low, but reliability deteriorates due to inability to mitigate multiple reflection errors
Solution Approach 1:
The patent incorporates feedback mechanisms within the phase-shifting algorithm that automatically identify and suppress signals at integer multiples of the fundamental frequency. The algorithm uses the known relationship between the modulation amplitude and harmonic frequencies to dynamically adjust sensitivity, providing self-correcting behavior that improves reliability without requiring complex external intervention or additional hardware
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
The proposed algorithm significantly reduces errors related to multiple reflections, enhancing the accuracy of phase difference determination and improving the reliability of sinusoidal phase-shifting interferometry in Fizeau interferometers.
Implementation Method 1
one can use an interferometer to combine a test wavefront reflected from a test surface with a reference wavefront reflected from a reference surface to form an optical interference pattern
Implementation Method 2
sinusoidally varying a phase between the test light and reference light, where the sinusoidal phase variation has an amplitude u
Data Source
AI summary
In certain aspects, disclosed methods include combining reference light reflected from a reference surface with test light reflected from a test surface to form combined light, the test and reference light being derived from a common source, sinusoidally varying a phase between the test light and reference light, where the sinusoidal phase variation has an amplitude u, recording at least one interference signal related to changes in an intensity of the combined light in response to the sinusoidal variation of the phase, determining information related to the phase using a phase shifting algorithm that has a sensitivity that varies as a function of the sinusoidal phase shift amplitude, where the sensitivity of the algorithm at 2 u is 10% or less of the sensitivity of the algorithm at u.