Self-Mixing Interferometric Signal Hilbert Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical devices for measuring target movement or distance, particularly those using self-mixing effects, are sensitive to surface finish and distance, leading to degraded interferometric signals due to optical feedback and speckle effects, limiting their effectiveness and adaptability.
Innovation Solution
An optical device and method that processes self-mixing interferometric signals by removing continuous components and determining interferometric peaks using a Hilbert filter, allowing for real-time measurement of target movement or distance without calibration, suitable for various surface finishes and distances, and eliminating hysteresis and fading effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If self-mixing interferometric measurement is used, then device compactness and cost are improved, but measurement precision deteriorates due to sensitivity to surface finish and distance
Solution Approach 1:
The patent applies parameter changes by transforming the interferometric signal through mathematical operations (Hilbert transform, continuous component removal) to change its characteristics. This allows the signal to be processed in a way that eliminates sensitivity to surface finish and distance variations, thereby maintaining measurement precision while preserving the compactness of the self-mixing device architecture
Solution Approach 2:
The patent introduces signal processing operations as an intermediary between the raw interferometric signal and the final measurement. The Hilbert transform and continuous component removal act as mediators that decouple the measurement precision from the problematic parameters (surface finish, distance), allowing the compact device to achieve high precision measurements
2Power
If optical feedback level increases, then signal strength is improved, but signal waveform quality deteriorates due to asymmetric sawtooth shape and hysteresis
Solution Approach 1:
The patent converts the harmful asymmetric sawtooth shape and hysteresis effects (which arise from high optical feedback) into beneficial features through mathematical transformation. The Hilbert transform and continuous component removal process these distorted waveforms to extract clean phase information, thereby converting the degraded signal quality into accurate measurement data while maintaining strong signal strength
3Length of moving object
If conventional interferometric devices are used, then measurement range is limited to short distances, but device complexity increases due to multiple optical components
Solution Approach 1:
The patent makes the laser light source multi-functional by using it both as the light source and as the interferometer (through self-mixing). This eliminates the need for separate external optical components like beam splitters and mirrors, extending the measuring range to long distances while keeping the device compact and simple. The laser cavity itself performs the interferometric measurement function
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
Enables precise, real-time measurement of target movement or distance with improved signal processing, reducing resource requirements and making the technology applicable in industrial settings without the need for external components or calibration.
Implementation Method 1
Some of the measuring beam is reflected by the target and reinjected into an active cavity of the laser source, producing interference in the active cavity of the laser source
Implementation Method 2
These fluctuations are detected either by a photodetector, such as for example a photodiode located on a back side of the laser light source
Data Source
AI summary
An optical device (10) for determining a physical parameter includes: a laser diode (11) for emitting a beam toward a target; an element for detecting (13) an interferometric signal SM(t) which includes the information on the physical parameter to be determined, and which is generated by an interference between the emitted beam and a light beam reflected by the target; element for converting (15) the signal SM(t) obtained by the detection element (13) into a measurement of the physical parameter, the conversion element (15) including: first element (17) for suppressing a continuous component Off(t) of the interferometric signal SM(t); second element (18) for determining interferometric peaks in the interferometric signal SM(t) obtained from the signal obtained at the output of the first element (17). An associated method, particularly suitable for speckle interferometric signals is also described.