Multi-Junction VCSEL SMI Sensing for Higher Signal-to-Noise Detection
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Solution Overview
Problem
Current optical sensing technologies, particularly those using self-mixing interferometry (SMI), face limitations in accurately detecting displacement, distance, motion, and velocity due to noise interference and limited signal-to-noise ratio, which affects the precision and reliability of sensors in various electronic devices.
Innovation Solution
The implementation of multi-junction vertical-cavity surface-emitting laser diodes (VCSELs) with associated photodiodes, which emit light in two directions and incorporate multiple tunnel junctions and quantum well layers, enhancing the signal-to-noise ratio and allowing for improved modulation of emitted laser light, thereby increasing the accuracy of distance and motion detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional VCSEL diodes are used in SMI sensors, then the device structure remains simple, but the signal-to-noise ratio is limited and measurement precision deteriorates
Solution Approach 1:
The VCSEL diode is divided into multiple junctions (first tunnel junction, second tunnel junction) with distinct functional regions. Each junction contributes to different aspects of light generation and modulation, enabling improved measurement precision through segmented functional optimization without creating a monolithic complex structure
Solution Approach 2:
Different regions of the VCSEL diode are assigned different doping concentrations and structural characteristics. The first and second tunnel junctions have different n-type and p-type layer doping levels, creating localized optimal conditions for light emission and self-mixing interference, thereby improving detection accuracy in specific functional zones
2Reliability
If multi-junction VCSEL diodes with multiple tunnel junctions are implemented, then signal-to-noise ratio and operating frequency improve, but device complexity increases
Solution Approach 1:
The VCSEL diode is divided into multiple junctions (first tunnel junction, second tunnel junction) with distinct functional regions. Each junction contributes to different aspects of light generation and modulation, enabling improved measurement precision through segmented functional optimization
Solution Approach 2:
The patent modifies key parameters including doping concentrations (n-type and p-type layers), junction configurations, and active region structures. These parameter changes optimize the signal-to-noise ratio and operating frequency by tuning the electrical and optical characteristics of each junction region
3Adaptability or versatility
If conventional single-junction VCSEL diodes are used, then manufacturing process remains simple, but wavelength modulation capability is limited
Solution Approach 1:
The VCSEL diode is divided into multiple junctions (first tunnel junction, second tunnel junction) with distinct functional regions. Each junction contributes to different aspects of light generation and modulation, enabling improved measurement precision through segmented functional optimization
Solution Approach 2:
The multi-junction VCSEL diode structure serves multiple functions: light generation, wavelength modulation, and self-mixing interference detection. The first and second tunnel junctions collectively provide both laser emission and modulation capabilities, reducing the need for separate components
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 configuration enhances the performance of SMI sensors by improving signal-to-noise ratio, increasing operating frequency, and providing better spatial resolution, leading to more precise detection of kinematic parameters such as distance and motion.
Implementation Method 1
The VCSEL diode may be configured to generate light within the resonance cavity, emit light toward an emission surface of the SMI sensor
Implementation Method 2
The semiconductor PD may be configured to produce a measurable electrical parameter related to the self-mixing
Implementation Method 3
optical sensing based on self-mixing interferometry (SMI)... self-mix the generated light with a reflection of the emitted light received into the resonance cavity
Data Source
AI summary
Disclosed herein are self-mixing interferometry (SMI) sensors that include a multi-junction (MJ) vertical-cavity surface-emitting laser (VCSEL) diode that emits laser light in two directions, one direction being directed toward a receiving photodiode and another toward an object. Reflections from the object induce self-mixing interference within a resonance cavity of the MJ-VCSEL altering a wavelength of the emitted laser light. The SMI may infer distance and/or motion of the object from the alterations in the wavelength. In various embodiments, the MJ-VCSEL and photodiode are successively formed as a single unit upon a single substrate. In other embodiments, the MJ-VCSEL and the photodiode may be formed on separate wafers or chips that are then joined at a common interface surface. Arrays of combinations of MJ-VCSELs and associated photodiodes may be included in an SMI.