Hybrid Interferometric Scatterometric Sensor for Low Optical Power Return
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Solution Overview
Problem
Coherent optical sensing systems, such as those using semiconductor lasers, face challenges in accurately characterizing targets due to low optical power return and noise interference, especially in demanding applications like particulate matter detection and surface profiling, due to the retro-reflective nature of self-mixing interferometry (SMI) and limited angular coherence of backscattered radiation.
Innovation Solution
The integration of both interferometric and scatterometric sensing techniques on a shared semiconductor substrate, where scatterometric sensors receive and process electromagnetic radiation not returned to the SMI sensor's resonant cavity, enhancing the signal-to-noise ratio and enabling higher resolution and accuracy in capturing spatial information from targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-mixing interferometry (SMI) is used for coherent optical sensing, then spatial information can be obtained with optical wavelength resolution and quantum limit signal levels, but the optical power of returned electromagnetic radiation is very low (less than 1 ppm of emitted power) due to the retro-reflective nature of the optical path
Solution Approach 1:
The invention segments the sensing function into two independent sensor types: SMI sensors for velocity detection and scatterometric sensors for position detection. This segmentation allows each sensor type to optimize its detection method for its specific function, with scatterometric sensors collecting scattered light at multiple angles rather than relying on the retro-reflective path of SMI sensors, thereby capturing more of the emitted optical power.
Solution Approach 2:
The patent creates a hybrid sensing system where a single optical source serves multiple functions: the same semiconductor laser emits radiation that is detected by both SMI sensors (for velocity) and scatterometric sensors (for position). This multi-functionality increases the overall utilization of the emitted optical power, as the scatterometric sensors capture light that would otherwise be lost in the SMI retro-reflective path.
2Reliability
If SMI sensors are used in demanding applications like particulate matter detection and surface profiling, then spatial information can be obtained, but the low optical power return and noise make it difficult to achieve accurate or high resolution characterizations
Solution Approach 1:
The invention merges SMI sensors and scatterometric sensors into a hybrid system that combines the advantages of both sensing methods. The scatterometric sensors provide robust position detection with higher optical power return, while SMI sensors provide velocity information. By merging these sensor types and fusing their data, the system achieves reliable and accurate characterization in demanding applications where either sensor type alone would be insufficient.
Solution Approach 2:
The hybrid system uses feedback from both SMI and scatterometric sensors to continuously refine the characterization of targets. The scatterometric sensors provide feedback on position and scattering properties, while SMI sensors provide feedback on velocity, allowing the system to adapt and improve its detection accuracy over time, particularly in challenging environments with low optical power return.
3Measurement precision
If scatterometric sensors are added to receive electromagnetic radiation not returned to the SMI sensor's resonant cavity, then the signal-to-noise ratio increases and spatial information capture improves, but the device complexity increases
Solution Approach 1:
The patent designs the sensor system so that the semiconductor substrate can support both SMI and scatterometric sensor structures using similar fabrication processes. The optical source serves both sensor types simultaneously, and the electrical interconnect structures are designed to handle signals from both sensor types. This multi-functional design minimizes the increase in device complexity while achieving improved signal-to-noise ratio through the addition of scatterometric sensing capability.
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 combination significantly improves the accuracy and resolution of spatial information capture, particularly for slow-moving or sparse targets, by increasing the optical power handling and reducing noise, thereby enhancing the fidelity of surface or sub-surface sensing.
Implementation Method 1
a semiconductor laser may generate and emit electromagnetic radiation from a resonant cavity of the semiconductor laser, receive returned (e.g., reflected or scattered) electromagnetic radiation back into the resonant cavity, self-mix the generated and returned electromagnetic radiation within the resonant cavity, and produce a self-mixing interferometry (SMI) signal
Implementation Method 2
The scatterometric sensors may receive much of the electromagnetic radiation that is emitted by an SMI sensor, returned from a target, but not received back into the resonant cavity of the SMI sensor
Data Source
AI summary
An optical sensor system including a semiconductor substrate; a self-mixing interferometry (SMI) sensor formed on the semiconductor substrate and including a semiconductor laser having a resonant cavity; and an array of photodetectors formed on the semiconductor substrate. The SMI sensor is configured to generate an SMI signal responsive to a retro-reflection of electromagnetic radiation emitted by the semiconductor laser and received into the resonant cavity. The array of photodetectors is configured to generate a set of angular-resolved scatter signals responsive to a scatter of the electromagnetic radiation emitted by the semiconductor laser.