Extending Spectrally Controlled Interferometry Range via Delay Line Modulation
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Solution Overview
Problem
Spectrally controlled interferometry struggles to form fringes at large distances from the reference surface due to the difficulty in achieving and controlling small spectral modulation periods, which are necessary for extended measurement ranges in applications like astronomy mirrors and large geometry systems.
Innovation Solution
Combining a spectrally controllable light source with an optical delay line, such as a Michelson interferometer, to superimpose multiple modulations on low-coherence light, allowing for the formation of localized fringes at extended distances by adjusting the optical path difference, thereby extending the measurement range of common-path interferometric configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If spectral modulation period is reduced to extend measurement range, then fringe formation distance is increased, but modulation control difficulty increases
Solution Approach 1:
The spectral modulation is divided into two separate components: a first modulation from the light source and a second modulation from the delay line. This segmentation allows each component to be optimized independently, with the delay line providing the fine-grained control needed for extended measurement ranges without overwhelming control complexity.
Solution Approach 2:
The delay line acts as an intermediary device that introduces the second spectral modulation. By placing this intermediate component between the light source and the interferometer, the system achieves extended measurement range while the delay line's mechanical simplicity reduces the overall control difficulty.
2Measurement precision
If common-path interferometer is used to eliminate coherent noise, then measurement accuracy is improved, but OPD balancing complexity increases
Solution Approach 1:
The system changes the spectral parameters of the light source through dual modulation rather than mechanically balancing the optical path difference. The first modulation controls the overall fringe pattern while the second modulation extends the measurement range, eliminating the need for complex OPD balancing while maintaining measurement accuracy.
3Object-affected harmful factors
If spectral modulation is used to achieve white light interferometry, then coherent noise is eliminated, but fringe formation at large distances becomes difficult
Solution Approach 1:
The patent merges two spectral modulations: one from the light source and one from the delay line. This combination allows the system to maintain the noise-canceling benefits of white light interferometry while extending the fringe formation distance to several meters through the additional modulation period introduced by the delay line.
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 the practice of spectrally controlled interferometry with extended measurement ranges, allowing fringes to form at significant distances without the need for mechanical scanning, while maintaining the advantages of common-path interferometry and reducing noise, as demonstrated by the ability to control fringe locations and contrast using sinusoidal modulations.
Implementation Method 1
a spectrally controllable light source modulated with low spectral frequency
Implementation Method 2
Spectrally controlled interferometry (SCI) is an interferometric technique that allows implementation of white light interferometry (WLI) measurement schemes in common-path interferometers
Implementation Method 3
Combining a spectrally controllable light source with an optical delay line, such as a Michelson interferometer, to superimpose multiple modulations on low-coherence light
Implementation Method 4
an optical delay line, such as provided by a Michelson interferometer
Implementation Method 5
WLI is characterized by the absence of coherent noise because of the light's short coherence length, typically on the order of a few micrometers
Implementation Method 6
Such arrangements can be complex and preclude the use of common-path interferometers, therefore forfeiting the advantages of WLI
Data Source
AI summary
The range of measurement in spectrally controlled interferometry (SCI) is extended by superimposing multiple modulations on the low-coherence light used for the measurement. Optimally, a spectrally controllable light source modulated sinusoidally with low spectral frequency is combined with a delay line, such as provided by a Michelson interferometer. The resulting light is injected into a Fizeau interferometer to generate localized fringes at a distance corresponding to the effect of the spectrally modulated source combined with the optical path difference produced by the delay line. The combination provides a convenient way to practice SCI with all its advantages and with a range that can be extended to the degree required for any practically foreseeable application. Alternatively, a single source capable of multiple modulations can be used instead of a separate second modulator component.