Self-Mixing Interferometry Distance Reference Stabilization
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Solution Overview
Problem
Self-mixing interferometry (SMI) based absolute distance measurement systems face significant errors due to temperature changes and degradation of light sources, leading to poor accuracy, especially in applications requiring high precision like tracking applications that need less than 0.5% error over 10 mm, where SMI-based measurements can have errors exceeding 15%.
Innovation Solution
Incorporating a distance reference with a known optical thickness, such as an optical film or block made of materials like glass, sapphire, or silicon, which has a well-defined low thermal expansion coefficient, to stabilize the measurement by relating disturbances in the SMI signal to the known optical thickness, thereby reducing wavelength-dependent errors and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If SMI-based distance measurement is used, then measurement speed and responsiveness are improved, but measurement precision deteriorates due to temperature changes and light source degradation
Solution Approach 1:
The patent introduces a distance reference object with known optical thickness as an intermediary element. This reference object provides stable, wavelength-independent interference patterns that mediate the measurement process, allowing the system to compensate for wavelength drift caused by temperature and aging effects while maintaining fast SMI measurement speeds.
Solution Approach 2:
The patent changes the measurement approach from direct wavelength-based measurement to optical thickness-based measurement. By measuring the optical thickness of the distance reference object (which has known material properties and low thermal expansion), the system transforms the measurement into a parameter that is less sensitive to environmental changes, thereby improving precision while maintaining speed.
2Measurement precision
If wavelength-based measurement is used, then measurement resolution is improved, but reliability deteriorates due to wavelength drift from temperature and aging
Solution Approach 1:
The distance reference object serves as a stable intermediary that does not suffer from wavelength drift. Its known optical thickness provides a reliable reference that remains constant despite changes in laser wavelength due to temperature or aging, thereby ensuring measurement reliability while maintaining high resolution through the interference pattern analysis.
Solution Approach 2:
The patent replaces direct optical wavelength measurement with an optical thickness measurement approach. By substituting the measurement of a physical dimension (optical thickness of the reference object) for wavelength measurement, the system eliminates the reliability issues associated with wavelength drift while preserving measurement resolution through precise optical interference analysis.
3Device complexity
If no distance reference is used, then device complexity is reduced, but measurement precision deteriorates due to uncorrected wavelength errors
Solution Approach 1:
The patent introduces a simple distance reference object with known optical thickness as an intermediary element. This reference object is physically simple and can be easily integrated into the measurement system, adding minimal complexity while providing the stability needed to correct wavelength errors and improve measurement precision significantly.
Solution Approach 2:
The patent changes the measurement parameter from direct wavelength measurement to optical thickness measurement of the reference object. This parameter change allows the system to maintain high precision by measuring a physical dimension (optical thickness) that is inherently more stable and less susceptible to environmental variations, while the added complexity of the reference object itself is minimal.
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 high accuracy SMI-based absolute distance measurement by stabilizing the measurement process with material properties and calibration, reducing errors to depend on the stability of the distance reference rather than wavelength variations, achieving better than 0.1 mm resolution.
Implementation Method 1
coherently or partially coherently self-mix the generated and reflected/backscattered electromagnetic radiation within the resonant cavity, and produce an output indicative of the self-mixing
Implementation Method 2
The optical element may have a known optical thickness between a first surface and a second surface of the optical element. The SMI sensor may be configured to emit a modulated beam of electromagnetic radiation toward the first surface of the optical element and generate an SMI signal containing disturbances caused by reflections or backscatters of the beam from the first surface and the second surface
Data Source
AI summary
A device includes a first component, a second component having a reconfigurable distance from the first component, an optical element, an SMI sensor, and a processor. The optical element has a fixed relationship with respect to the first component, and has a known optical thickness between a first surface and a second surface of the optical element. The SMI sensor has a fixed relationship with respect to the second component, and has an electromagnetic radiation emission axis that intersects the first and second surfaces of the optical element. The processor is configured to identify disturbances in an SMI signal generated by the SMI sensor, relate the disturbances to the known optical thickness of the optical element, and to determine a distance between the first and second components using the SMI signal and the relationship of the disturbances to the known optical thickness of the optical element.