Photonic Resonant Accelerometer Using Optical Tether Sensing
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Solution Overview
Problem
Conventional MEMS accelerometers face challenges in detecting low-level accelerations due to limited sensitivity and stability, particularly in harsh environments, and often require larger size and higher power consumption to achieve better performance.
Innovation Solution
The development of photonic integrated resonant accelerometers (PIRAs) that utilize evanescently coupled ring resonators and optically sensed tethers to measure acceleration, allowing for reduced tether dimensions and improved scale factors, while maintaining low size, weight, and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MEMS accelerometers use capacitive pickoffs to measure proof mass displacement, then the device structure is simple and manufacturing is easy, but the sensitivity is insufficient for detecting sub milliG accelerations
Solution Approach 1:
The patent replaces the conventional capacitive sensing mechanism with an optical sensing system. Light is coupled into a resonator that interacts with the tether through evanescent field coupling. When the tether moves due to acceleration, it modulates the resonator's optical resonance condition, enabling detection of sub milliG accelerations with high sensitivity while maintaining a relatively simple device structure.
Solution Approach 2:
The patent changes the measurement parameter from direct capacitive displacement measurement to optical resonance condition monitoring. By monitoring changes in the resonator's resonance frequency and quality factor in response to tether movement, the system achieves enhanced acceleration sensitivity beyond what conventional capacitive pickoffs can provide.
2Measurement precision
If displacement-based accelerometers use highly sensitive interferometric measurement, then the resolution can reach 10^-9 g, but the device requires large size and high power consumption
Solution Approach 1:
The patent replaces bulky interferometric measurement systems with a compact optical resonator-based sensing mechanism. The resonator is integrated close to the tether, allowing evanescent field coupling without requiring complex interferometric paths. This substitution achieves high resolution acceleration measurement while dramatically reducing device size and power consumption.
Solution Approach 2:
The patent nests the optical resonator in close proximity to the tether, with the resonator positioned within the evanescent field region of the tether. This nested configuration allows the sensing function to be integrated within the existing accelerometer structure, eliminating the need for separate, large-scale interferometric measurement systems.
3Measurement precision
If optical accelerometers use evanescent optical coupling to measure minute displacements, then the measurement sensitivity is high, but the scale factor stability and dynamic range are restricted in open-loop mode
Solution Approach 1:
The patent implements a feedback mechanism where the detected resonance condition changes are used to adjust the drive frequency or other system parameters. This feedback loop compensates for drift and non-linearities, maintaining scale factor stability and extending the dynamic range while preserving the high sensitivity benefits of evanescent optical coupling.
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
PIRAs achieve higher sensitivity and stability, with scale factors exceeding 1 kHz/g and bias stability down to 100 ng, enabling accurate acceleration measurements in small form factors and harsh conditions.
Implementation Method 1
A ring resonator is evanescently coupled to the tether. Vibration of the tether causes a change of the resonance condition of the ring resonator.
Implementation Method 2
Resonant accelerometers (also referred to as frequency-modulated accelerometers) can relieve the constraints in displacement-based accelerometers by sensing acceleration based on detection of the resonant frequency of the tethers that suspend the proof mass.
Data Source
AI summary
The accelerometers disclosed herein provide excellent sensitivity, long-term stability, and low SWaP-C through a combination of photonic integrated circuit technology with standard micro-electromechanical systems (MEMS) technology. Examples of these accelerometers use optical transduction to improve the scale factor of traditional MEMS resonant accelerometers by accurately measuring the resonant frequencies of very small (e.g., about 1 μm) tethers attached to a large (e.g., about 1 mm) proof mass. Some examples use ring resonators to measure the tether frequencies and some other examples use linear resonators to measure the tether frequencies. Potential commercial applications span a wide range from seismic measurement systems to automotive stability controls to inertial guidance to any other application where chip-scale accelerometers are currently deployed.