An Optical Measuring Transducer for a Micro-Opto-Electro-Mechanical Micro-g Accelerometer Based on the Optical Tunneling Effect

Abstract

Micro-opto-electro-mechanical (MOEM) accelerometers that can measure small accelerations are attracting growing attention thanks to their considerable advantages—such as high sensitivity and immunity to electromagnetic noise—over their rivals. In this treatise, we analyze 12 schemes of MOEM-accelerometers, which include a spring mass and a tunneling-effect-based optical sensing system containing an optical directional coupler consisting of a fixed and a movable waveguide separated by an air gap. The movable waveguide can perform linear and angular movement. In addition, the waveguides can lie in single or different planes. Under acceleration, the schemes feature the following changes to the optical system: gap, coupling length, overlapping area between the movable and fixed waveguides. The schemes with altering coupling lengths feature the lowest sensitivity, yet possess a virtually unlimited dynamic range, which makes them comparable to capacitive transducers. The sensitivity of the scheme depends on the coupling length and amounts to 11.25 × 103 m−1 for a coupling length of 44 μm and 30 × 103 m−1 for a coupling length of 15 μm. The schemes with changing overlapping areas possess moderate sensitivity (1.25 × 106 m−1). The highest sensitivity (above 6.25 × 106 m−1) belongs to the schemes with an altering gap between the waveguides.

The Design, Modeling and Experimental Investigation of a Micro-G Microoptoelectromechanical Accelerometer with an Optical Tunneling Measuring Transducer

“…The acceleration that is equivalent to the mechanical thermal noise of the accelerometer's MSE can be determined as follows [14,32]:…”

“…In this case, the electrostatic force worked against gravity and compensated for the arising displacement of the MSE. The optical transmission coefficient of the directional coupler is determined as [32,37] 2 cos ,…”

“…In work [35], we presented the dependencies of the difference between the effective indices of the even and off modes of the gap that is inserted into Equation ( 5). More details on the selection of the displacement type of the moving waveguide and the optical measuring transducer working principle can be found elsewhere [9,32].…”

“…The directional coupler is the basic functional element of the MOEM accelerometer's optical transducer that has the highest practical potential. The designs of MOEM accelerometers with optical displacement sensors based on the tunneling effect are highly promising in terms of the achievable compactness and high sensitivity [32][33][34]. To increase the sensitivity, optical resonators are used; however, they are highly sensitive to temperature.…”

Characterization of Sensitivity of Time Domain MEMS Accelerometer

“…Based on transducers that convert the applied acceleration perturbation into changes in displacement, the developed accelerometers include capacitive sensors [3,8], tunneling sensors [9], piezoresistive sensors [10], and piezoelectric sensors [11], where both the proof mass and elastic beam of the developed acceleration sensors are under a quasi-static state. The sensitivities of these sensors can be improved via lowering the natural frequency of the sensor.…”