VCSEL SMI Laser Sensor Polarizer Layout for Modulation Suppression
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Solution Overview
Problem
State-of-the-art SMI laser sensors face challenges in efficiently removing the modulation signal from the detected photo signal, leading to a significantly reduced signal-to-noise ratio due to hardware noise introduction or high ADC bit requirements in post-processing.
Innovation Solution
Employ a cross polarizer with a passing polarization orthogonal to the linear polarization of the VCSEL to suppress the modulation signal in the optical domain, using absorptive or beam-splitting polarizers to ensure the detected signal consists only of self-mixing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hardware demodulation is used to remove modulation signal, then modulation removal is achieved, but additional noise is introduced reducing signal-to-noise ratio
Solution Approach 1:
The patent replaces hardware-based mechanical/electrical demodulation systems with an optical domain solution using polarizers. Instead of using complex hardware circuits to remove modulation signals, the invention uses optical polarization filtering to achieve the same goal without introducing additional noise, thereby maintaining signal-to-noise ratio.
Solution Approach 2:
The patent introduces a polarizer as an intermediary optical element between the VCSEL and photodetector. This polarizer acts as a mediator that selectively filters modulation signals based on their polarization state, allowing the desired SMI signal to pass while blocking the unwanted modulation component without adding noise.
2Measurement precision
If post processing is used to remove modulation contribution, then modulation removal is achieved, but large amount of ADC bits and low gain amplification are required
Solution Approach 1:
The patent performs modulation removal in advance in the optical domain using polarizers, before the signal reaches the photodetector and ADC. By removing the modulation contribution preliminarily through optical filtering, the subsequent electronic processing requires fewer ADC bits and simpler amplification, reducing overall system complexity.
3Stability of the object's composition
If VCSEL emits linearly polarized light, then single-mode operation is achieved, but modulation signal cannot be suppressed without additional optical elements
Solution Approach 1:
The patent exploits polarization state changes as a form of optical property differentiation. By using a polarizer oriented at 45 degrees to the VCSEL's linear polarization, the system creates a configuration where the modulation signal (which maintains the original polarization) is suppressed while the SMI signal (which experiences polarization rotation) can be detected, effectively using polarization 'color' differentiation.
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
Achieves a significant enhancement of the signal-to-noise ratio by effectively removing modulation in the optical domain without additional hardware or post-processing, enhancing the clarity of distance and velocity measurements.
Implementation Method 1
a linear polarizer arranged in front of the photodetector such that the laser radiation passes through the linear polarizer before reaching the photodetector. An orientation of a passing polarization of the linear polarizer differs from the linear polarization of the laser radiation of the VCSEL by an angle different from zero.
Implementation Method 2
a photodetector configured to monitor the laser radiation of the VCSEL
Implementation Method 3
a vertical cavity surface emitting laser, VCSEL, configured to emit laser radiation with a linear polarization through an emission surface
Implementation Method 4
comprise a gain region that is sandwiched between two distributed Bragg reflectors, DBR, acting as end mirrors
Data Source
AI summary
A self-mixing interferometric (SMI) laser sensor includes a vertical cavity surface emitting laser (VCSEL) configured to emit laser radiation with a linear polarization through an emission surface. The SMI laser sensor also includes a photodetector configured to monitor the laser radiation of the VCSEL. The SMI laser sensor further includes a linear polarizer arranged in front of the photodetector such that the laser radiation passes through the linear polarizer before reaching the photodetector. An orientation of a passing polarization of the linear polarizer differs from the linear polarization of the laser radiation of the VCSEL by an angle different from zero.