Dual-VCSEL Interferometry for Temperature-Stable Proximity Sensing
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Solution Overview
Problem
Conventional proximity sensors are highly susceptible to temperature changes, leading to variations in electrical and optical properties due to thermal expansion or contraction, which increases design complexity, component cost, and power consumption, and affects the accuracy of distance and velocity measurements.
Innovation Solution
An optical proximity sensor utilizing two discrete vertical cavity surface-emitting lasers (VCSELs) for self-mixing interferometry, where one VCSEL illuminates an object to determine distance and velocity, and another VCSEL illuminates a fixed surface to calibrate measurements, thereby mitigating the effects of temperature and environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional proximity sensors are used, then distance and velocity measurements can be obtained, but the measurements are highly susceptible to temperature changes and environmental variations
Solution Approach 1:
The patent uses two VCSELs operating at different wavelengths (first VCSEL at wavelength λ1, second VCSEL at wavelength λ2) to measure the same physical distance. By comparing the interference patterns from both wavelengths, the system can distinguish between changes caused by temperature (affecting both wavelengths similarly) and changes caused by actual object movement (affecting the measurement differently). This wavelength diversity approach allows temperature compensation while maintaining measurement precision.
2Measurement precision
If additional components are added to compensate for temperature effects, then measurement accuracy improves, but design complexity and component cost increase
Solution Approach 1:
The patent combines two VCSELs and their respective optical paths into a single integrated sensor system. Both VCSELs share common components including the housing, lens, beam splitter, and photodetector, allowing the system to achieve temperature compensation functionality without proportionally increasing overall system complexity. The shared optical path and processing electronics reduce the incremental complexity compared to using completely separate sensing systems.
Solution Approach 2:
The second VCSEL serves multiple functions: it provides a reference measurement for temperature compensation, validates the optical path integrity, and can be used to monitor environmental conditions. This multi-functionality approach allows a single additional VCSEL to address multiple potential issues (temperature drift, optical path blockage, calibration) without requiring separate dedicated components for each function.
3Device complexity
If conventional proximity sensors are used, then the sensor structure remains simple, but thermal expansion causes changes in electrical and optical properties affecting measurement accuracy
Solution Approach 1:
The patent exploits the fact that thermal expansion affects the optical path length in a predictable manner that is wavelength-dependent. By measuring at two different wavelengths and analyzing the differential phase shifts, the system can mathematically separate the thermal expansion component from the actual object distance component, thereby compensating for thermal effects without fundamentally changing the basic interferometric sensor structure.
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 solution provides calibrated measurements that are substantially independent of temperature and environmental variations, reducing variability and maintaining accuracy in distance and velocity determinations.
Implementation Method 1
Both vertical cavity surface-emitting lasers are configured for self-mixing interferometry. The first vertical cavity surface-emitting laser is configured to illuminate an object to determine a distance to and/or a velocity of that object based on self-mixing interferometry.
Data Source
AI summary
An optical proximity sensor includes a first vertical cavity surface-emitting laser configured for self-mixing interferometry to determine distance to and/or velocity of an object. The optical proximity sensor also includes a second vertical cavity surface-emitting laser configured for self-mixing interferometry to determine whether any variation in a fixed distance has occurred. The optical proximity sensor leverages output from the second vertical cavity surface-emitting laser to calibrate output from the second vertical cavity surface-emitting laser to eliminate and/or mitigate environmental effects, such as temperature changes.