Abstract
Optical coupling between subwavelength grating pairs allows for the precise measurement of lateral or vertical displacement of grating elements and gives rise to different types of displacement and inertial sensors. In this paper, we demonstrate a design for a nano-optomechanical accelerometer based on a subwavelength grating pair that can be easily fabricated by a single Silicon-on-insulator (SOI) chip. The parameters of the subwavelength grating pair-based optical readout, including period, duty cycle, thickness of grating and metal film, and the distance of the air gap, were optimized by combining a genetic algorithm and rigorous coupled wavelength analysis (RCWA) to obtain the optimal sensitivity to the displacement of suspended grating element and the acceleration. A corresponding mechanical design was also completed to meet the highly sensitive acceleration measurement requirement while considering the mechanical cross-axis sensitivity, dynamic range, bandwidth, and fabrication feasibility. This device was verified by both RCWA and finite-different-time-domain methods, and a tolerance analysis was also completed to confirm that it is able to achieve the extremely high optical displacement sensitivity of 1.8%/nm, acceleration-displacement sensitivity of 1.56 nm/mg, and acceleration measurement sensitivity of more than 2.5%/mg, which is almost one order of magnitude higher than any reported counterparts. This work enables a single SOI-based high performance accelerometer, and provides a theoretical basis and fabrication guides for the design.
Highlights
A considerable demand for high-performance inertial sensors has been growing in areas such as inertial navigation, seismic monitoring, and attitude control
Inspired by the polarization selectivity of the subwavelength grating, we propose a nano-optomechanical accelerometer based on a newly designed subwavelength grating pair
The optical readout was insensitive to the displacement along the y-axis if the grating area was larger than the beam size, and the acceleration-displacement sensitivity along the y-axis was far smaller than that Sensors along2018, the18,x-axis under the premise that l3
Summary
A considerable demand for high-performance inertial sensors has been growing in areas such as inertial navigation, seismic monitoring, and attitude control. The subwavelength grating pair, which served as a highly sensitive optical displacement readout, was located at the center of a relatively bulky plate, which was made by the device layer of a SOI wafer. The settings of the elastic spring-mass structure, including the size of the plate and the dimensions and shape of the beams were optimized to obtain low mechanical cross-axis sensitivity and relatively high acceleration-displacement sensitivity by using analytical calculations and finite element modeling (FEM). Both the subwavelength grating pair and elastic structure can be fabricated with a SOI wafer. Combined with the corresponding mechanical design that has acceleration-displacement sensitivity of 1.56 nm/g, this sensor can realize high acceleration sensitivity of 2.8%/mg, proving itself as a potential high-performance and fabricated inertial sensor
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