Variable Wavelength Interferometer for Picometer Metrology
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Solution Overview
Problem
Current measurement technologies, such as Michelson interferometers and frequency combs, have limited dynamic range and are not sufficient for the increasing precision requirements of future telescopes, particularly in space-based systems like the James Webb Space Telescope, which need to measure displacements with higher accuracy.
Innovation Solution
A light-based metrology system using a variable wavelength light source in combination with a Michelson interferometer and a frequency comb generator to achieve high dynamic range picometer-scale displacement measurements, where the wavelength of the light source is adjusted to maintain constant interference pattern intensity and heterodyne signals are used to determine displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Michelson interferometers are used for displacement measurement, then measurement precision is improved, but dynamic range deteriorates
Solution Approach 1:
The patent applies dynamics by making the measurement arm length variable and adjustable. The interferometer transitions from a static configuration to a dynamic one where the measurement arm can be extended or adjusted to accommodate different measurement ranges. This allows the system to maintain high precision across a broader dynamic range by adapting the arm length to the specific measurement requirements.
Solution Approach 2:
The patent changes physical parameters of the interferometer system, specifically the arm length and optical configuration. By varying these parameters, the system can optimize both precision and dynamic range for different measurement scenarios. The ability to change parameters allows the instrument to resolve the contradiction between fixed precision requirements and variable dynamic range needs.
2Measurement precision
If frequency combs are used for sub picometer measurements, then measurement precision is improved, but device complexity deteriorates
Solution Approach 1:
The patent extracts and utilizes only the essential frequency comb functionality needed for the measurement, rather than implementing a full frequency comb system. By taking out only the necessary components and functions, the system achieves sub-picometer precision without the complete complexity of a full frequency comb implementation.
Solution Approach 2:
The patent introduces an intermediary approach by using the frequency comb technique in a simplified manner within the interferometer framework. This intermediary method allows the system to benefit from frequency comb precision advantages while avoiding the full complexity of a dedicated frequency comb system.
3Measurement precision
If Fabry Perot resonances are used for displacement monitoring, then measurement precision is improved, but alignment sensitivity deteriorates
Solution Approach 1:
The patent inverts the approach by using Michelson interferometry with variable arm length instead of Fabry-Perot resonance. This inversion allows the system to achieve comparable or superior precision while dramatically reducing alignment sensitivity, as the Michelson configuration is inherently more robust to alignment variations.
Solution Approach 2:
The patent substitutes the mechanically sensitive Fabry-Perot resonant cavity with a Michelson interferometer configuration that is less sensitive to mechanical alignment. This substitution maintains measurement precision while reducing the difficulty of detecting and measuring alignment variations.
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 system enables precise picometer-scale displacement measurements with a high dynamic range, allowing for accurate alignment and adjustment of optical systems, such as telescopes, by converting heterodyne signals into displacement measurements, effectively addressing the limitations of existing technologies.
Implementation Method 1
The measurement beam is reflected from the surface of the mirror segment being measured, and is recombined with the reference beams. The fringe pattern that results from the interference is then analyzed.
Implementation Method 2
Light from the variable wavelength light source is also supplied to an optical combiner, where it is mixed with light from a reference frequency generator. The resulting heterodyne signal is received at a second photodetector
Data Source
AI summary
Systems and methods for measuring displacements at the picometer level are provided. A system can include a Michelson interferometer having a fixed arm and a measurement arm. As the length of the measurement arm changes, the output supplied to the interferometer from a variable wavelength light source is changed until the intensity of the resulting inference pattern is maximized. The wavelength of the light at the point the interference pattern is maximized is then measured by mixing light from the light source with the output from a frequency comb generator. The resulting frequency measurement is then converted to a length measurement.