MEMS Interferometer Self-Calibration via Capacitive Sensing
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Solution Overview
Problem
Existing optical interferometers face challenges in accurately determining the position of a movable mirror without increasing system size, cost, and complexity, as traditional methods require bulky laser sources and additional interferometers.
Innovation Solution
A Micro-Electro-Mechanical System (MEMS) apparatus with a movable mirror and a MEMS actuator having variable capacitance, coupled with a capacitive sensing circuit and digital signal processor for self-calibration, allowing for precise determination of mirror position using capacitance measurements and correction calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser and auxiliary interferometer are used to measure the moving mirror position, then measurement precision is improved, but device complexity and size increase
Solution Approach 1:
The patent combines the mirror position sensing function with the existing interferometer system by using the interferometer's own optical components (beam splitter, fixed mirror, detector) to generate interference patterns that encode position information. This eliminates the need for separate laser sources and auxiliary interferometers, reducing device complexity while maintaining measurement precision through the integrated optical path.
Solution Approach 2:
The interferometer system is designed to serve multiple functions: it simultaneously performs spectral analysis and mirror position measurement. The same optical components (beam splitter, mirrors, detector) are used for both the primary interferometric measurement and the position sensing function, allowing one system to fulfill multiple roles without requiring additional dedicated components.
2Measurement precision
If a laser and auxiliary interferometer are used to measure the moving mirror position, then measurement precision is improved, but system size increases
Solution Approach 1:
The patent merges the position measurement function into the existing interferometer structure, using the same optical path and components for both spectral analysis and position sensing. This integration eliminates the need for separate bulky laser sources and auxiliary interferometer equipment, significantly reducing the overall system size while maintaining accurate mirror position measurement capabilities.
3Measurement precision
If a laser and auxiliary interferometer are used to measure the moving mirror position, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent integrates mirror position measurement functionality into the existing interferometer system, eliminating the need for separate laser sources and auxiliary interferometer components. This consolidation reduces the total component count and system complexity, leading to lower manufacturing costs while maintaining the required measurement precision through the shared optical path and components.
4Measurement precision
If mechanical stoppers are used for drift correction, then measurement precision is improved, but reliability decreases due to mechanical constraint and damage risk
Solution Approach 1:
The patent replaces the mechanical stopper-based drift correction system with an optical sensing approach. Instead of using physical mechanical constraints that risk damage, the system uses interference pattern detection and capacitive sensing to identify and correct drift, eliminating mechanical contact and improving reliability while maintaining correction accuracy.
Solution Approach 2:
The system performs self-correction of drift by continuously monitoring its own state through interference pattern analysis and capacitive sensing. The drift correction is achieved through software algorithms that process the optical and electrical signals, allowing the system to self-regulate without external mechanical intervention, thereby improving reliability and reducing mechanical wear.
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
Enables accurate and self-calibrated mirror positioning within MEMS interferometers, reducing system size, cost, and complexity while maintaining high accuracy, facilitating integration into compact devices.
Implementation Method 1
a MEMS actuator having a variable capacitance that is coupled to the moveable mirror to cause a displacement thereof
Implementation Method 2
the capacitive sensing circuit measures a capacitance variation as the moveable mirror moves through at least two zero crossings of an interference pattern produced as a result of the input beam and movement of the moveable mirror
Data Source
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AI summary
A Micro-Electro-Mechanical System (MEMS) interferometer provides for self-calibration of mirror positioning of a moveable mirror. The moveable mirror is coupled to a MEMS actuator having a variable capacitance. The MEMS interferometor includes a capacitive sensing circuit for determining the capacitance of the MEMS actuator at two or more known positions of the moveable mirror and a calibration module for using the actuator capacitances at the known positions to compensate for any drift in the capacitive sensing circuit.