Integrated Waveguide Optical Pickoff for MEMS Sensors
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Solution Overview
Problem
Capacitive readouts in MEMS sensors are prone to errors such as electrical feed-through and damping, and existing optical evanescent coupling methods are not robust enough to handle harsh environmental factors, limiting their effectiveness in measuring both vertical and horizontal motion.
Innovation Solution
A time-based optical pickoff system integrated within a MEMS sensor's glass substrate, utilizing an integrated waveguide with an optical input port, coupling port, and output port to detect changes in light attenuation caused by in-plane motion of a moving sensor component, providing high sensitivity and stability by measuring the attenuation of a light beam as the component moves relative to the waveguide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capacitive readout is used in MEMS sensors, then the readout mechanism is simple to implement, but the sensor is susceptible to electrical errors such as feed-through, damping, and work function changes
Solution Approach 1:
The patent replaces the electrical capacitive readout mechanism with an optical readout mechanism. Specifically, it uses evanescent field coupling between a waveguide and a moving sensor component to detect displacement, thereby eliminating susceptibility to electrical errors such as feed-through, damping, and work function changes while maintaining manufacturing feasibility through integrated waveguide fabrication
Solution Approach 2:
The patent introduces an optical intermediary (evanescent field) between the moving sensor component and the detection system. The evanescent field couples light from the waveguide to the sensor component, providing a non-contact, electrical-error-free measurement mechanism that bridges the mechanical motion and optical detection
2Measurement precision
If optical evanescent coupling is used for readout, then sensitivity is improved, but the system is not rugged enough to handle harsh environmental factors
Solution Approach 1:
The patent merges the optical waveguide and the sensor component into a single integrated structure where the waveguide is monolithically formed with the sensor component. This integration protects the evanescent coupling interface from environmental damage while maintaining high sensitivity, as the coupled structure is more robust than separate components
Solution Approach 2:
The patent uses composite material structures combining different materials (e.g., silicon nitride waveguides with silicon sensor components) to achieve both the optical coupling functionality and environmental robustness. The composite structure allows optimization of each material for its specific function while providing overall system durability
3Measurement precision
If optical coupling is used to measure vertical displacement, then high sensitivity is achieved, but horizontal motion detection capability is limited
Solution Approach 1:
The patent extends the optical coupling geometry from vertical (out-of-plane) to horizontal (in-plane) by positioning the waveguide adjacent to the side of the moving sensor component. This dimensional change enables detection of horizontal motion while maintaining the evanescent coupling mechanism, thereby adding versatility without sacrificing vertical sensitivity
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 system achieves high sensitivity and stability in measuring both vertical and horizontal motion of MEMS sensor components, overcoming the limitations of capacitive readouts and existing optical methods by using evanescent coupling to detect changes in light intensity, enabling accurate in-plane motion detection with positional resolution of a few microns.
Implementation Method 1
Optical evanescent coupling is a promising readout technique that is potentially more sensitive than its capacitive counterpart
Implementation Method 2
detecting changes in an area of overlap between the coupling port and a moving sensor component separated from the coupling port by a gap by measuring an attenuation of the light beam at the optical output port
Data Source
AI summary
Systems and methods for a time-based optical pickoff for MEMS sensors are provided. In one embodiment, a method for an integrated waveguide time-based optical-pickoff sensor comprises: launching a light beam generated by a light source into an integrated waveguide optical-pickoff monolithically fabricated within a first substrate, the integrated waveguide optical-pickoff including an optical input port, a coupling port, and an optical output port; and detecting changes in an area of overlap between the coupling port and a moving sensor component separated from the coupling port by a gap by measuring an attenuation of the light beam at the optical output port, wherein the moving sensor component is moving in-plane with respect a surface of the first substrate comprising the coupling port and the coupling port is positioned to detect movement of an edge of the moving sensor component.