Self-Mixing Interferometry Sensor Optical Power Ratio
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Solution Overview
Problem
Existing self-mixing interferometry (SMI) sensor modules face challenges in determining an optimal optical power ratio, leading to lower signal-to-noise ratios (SNR) and reduced accuracy in distance and speed measurements due to inadequate power splitting between the target and detector units.
Innovation Solution
A self-mixing interferometry sensor module with an optical element that adjusts the splitting ratio of transmitted and reflected electromagnetic radiation to achieve an optimal power ratio, ensuring sufficient light is directed towards both the target and detector for accurate SMI signal measurement, using a predetermined value for the TBS/RBS ratio to balance SNR and SMI feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If more light is directed towards the detector unit to improve signal detection, then the signal-to-noise ratio improves, but the self-mixing interference feedback level decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the optical power ratio (splitting ratio) between the fraction of light directed to the detector and the fraction directed to the target. By adjusting this parameter to a predetermined optimal value, the system balances the signal-to-noise ratio at the detector with the self-mixing interference feedback level, resolving the contradiction between improving measurement precision and maintaining reliability.
2Reliability
If more light is directed towards the target to maintain SMI feedback, then the self-mixing interference signal is strengthened, but the signal-to-noise ratio at the detector decreases
Solution Approach 1:
The patent resolves this contradiction by changing the optical power ratio parameter to an optimal predetermined value. This optimization ensures that sufficient light reaches the target to maintain reliable self-mixing interference feedback while simultaneously directing adequate light to the detector to achieve a high signal-to-noise ratio for accurate measurements.
3Measurement precision
If the optical power ratio is not optimized, then the device complexity is reduced, but the measurement accuracy decreases
Solution Approach 1:
The patent applies preliminary action by pre-determining the optimal optical power ratio value before actual measurement operations. This predetermined optimization parameter is established in advance through theoretical analysis and simulation, allowing the system to achieve high measurement accuracy without requiring complex real-time adjustment mechanisms, thus balancing measurement precision with device complexity.
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 enhances the signal-to-noise ratio and accuracy of distance and speed measurements by optimizing the optical power ratio, ensuring that the SMI feedback remains within an optimal level, thereby improving the overall performance of the sensor module.
Implementation Method 1
Self-mixing interference occurs when part of the light emitted from a coherent light source is retro-fed back into the coherent source cavity (e.g., a laser such as a vertical-cavity surface-emitting laser, or VCSEL, or as a distributed feedback laser, or DFB). In turn, the coherent light source cavity produces a change in carrier population and refractive index.
Implementation Method 2
The optical element is aligned with respect to the light emitter such that a first fraction of electromagnetic radiation is directed towards the external target and/or the light emitter and a second fraction of electromagnetic radiation is directed towards the detector unit
Implementation Method 3
a first fraction of electromagnetic radiation is directed towards the external target and/or the light emitter and a second fraction of electromagnetic radiation is directed towards the detector unit
Implementation Method 4
The power readout unit may be composed of a photodetector or a photodetector array. In this case, the readout unit has to interact with the optical beam path of the coherent light source to sample the SMI signal.
Data Source
AI summary
A self-mixing interferometry sensor module, comprising a light emitter (LE), a detector unit (DU) and an optical element (OE), wherein the light emitter (LE) is operable to emit coherent electromagnetic radiation towards an external object (ET) to be placed outside the sensor module and undergo self-mixing interference, SMI, caused by reflections of the emitted electromagnetic radiation from the external object back inside the sensor module. The detector unit (DU) is operable to generate output signals indicative of an optical power output of the light emitter (LE) due to the SMI. The optical element (OE) is aligned with respect to the light emitter (LE) such that a first fraction of electromagnetic radiation is directed towards the external target (ET) or the light emitter (LE) and a second fraction of electromagnetic radiation is directed towards the detector unit (DU). An optical power ratio determined by the first and second fractions meets a pre-determined value.