VCSEL Optical Displacement Sensor with Membrane Cavity
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Solution Overview
Problem
Conventional optical displacement sensors face challenges with squeezed-film damping due to the close proximity of the membrane to the substrate, limiting their sensitivity and frequency range, especially when used as optical microphones, pressure sensors, or accelerometers.
Innovation Solution
The use of a vertical-cavity surface-emitting laser (VCSEL) with a membrane suspended above the VCSEL, forming a second optical cavity that reduces squeezed-film damping by allowing a larger separation, enabling changes in lasing characteristics and intensity in response to displacement, which is detected by a photodetector to generate an electrical output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the membrane is located very close to the substrate, then the optical path length is reduced and device compactness is improved, but squeezed-film damping increases which reduces sensitivity and frequency range
Solution Approach 1:
The patent introduces an optical cavity as an intermediary space between the membrane and substrate. This cavity, filled with air or vacuum, acts as a mediator that transmits optical signals while preventing direct mechanical interaction between the membrane and substrate, thereby eliminating squeezed-film damping effects that would otherwise occur in direct-contact configurations
Solution Approach 2:
The patent replaces direct mechanical coupling between the membrane and substrate with an optical coupling mechanism. Instead of mechanical contact that causes damping, the system uses light transmission through the membrane and optical feedback into the VCSEL to sense displacement, substituting mechanical interaction with optical interaction that does not suffer from squeezed-film damping
2Reliability
If the membrane is suspended at a larger separation from the VCSEL, then squeezed-film damping is reduced, but the optical cavity length increases which may affect device compactness
Solution Approach 1:
The patent optimizes the optical cavity length parameter to achieve the desired balance. By carefully selecting the cavity length within a specific range, the system maintains reduced squeezed-film damping while controlling the overall device footprint, demonstrating parameter optimization to resolve the contradiction between sensitivity improvement and compactness maintenance
3Measurement precision
If optical feedback is implemented into the VCSEL, then displacement detection sensitivity is improved through changes in lasing characteristics, but device complexity increases
Solution Approach 1:
The patent implements a self-service mechanism where the VCSEL serves dual functions: it acts as both the light source and the displacement sensor. The optical feedback from the membrane directly modulates the VCSEL's lasing characteristics, allowing the device to self-detect displacement without requiring separate sensing components, thereby reducing overall system complexity despite the sophisticated detection mechanism
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 sensitivity and frequency range by minimizing squeezed-film damping, allowing for effective detection of sound, vibrations, and accelerations while maintaining a compact design, and can be batch fabricated for various applications.
Implementation Method 1
a vertical-cavity surface-emitting laser (VCSEL) comprising a first optical cavity with an active region therein to produce a beam of lasing light
Implementation Method 2
the membrane and the output mirror forming a second optical cavity which is coupled to the first optical cavity
Implementation Method 3
a photodetector to detect the change in intensity of the beam of lasing light from the VCSEL and to generate therefrom an electrical output signal which varies with the displacement of the membrane
Data Source
AI summary
An optical displacement sensor is disclosed which uses a vertical-cavity surface-emitting laser (VCSEL) coupled to an optical cavity formed by a moveable membrane and an output mirror of the VCSEL. This arrangement renders the lasing characteristics of the VCSEL sensitive to any movement of the membrane produced by sound, vibrations, pressure changes, acceleration, etc. Some embodiments of the optical displacement sensor can further include a light-reflective diffractive lens located on the membrane or adjacent to the VCSEL to control the amount of lasing light coupled back into the VCSEL. A photodetector detects a portion of the lasing light from the VCSEL to provide an electrical output signal for the optical displacement sensor which varies with the movement of the membrane.