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

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 x 10(3) m(-1) for a coupling length of 44 mu m and 30 x 10(3) m(-1) for a coupling length of 15 mu m. The schemes with changing overlapping areas possess moderate sensitivity (1.25 x 10(6) m(-1)). The highest sensitivity (above 6.25 x 10(6) m(-1)) belongs to the schemes with an altering gap between the waveguides.