A System for Positioning an Optical Tunnel Measuring Transducer of a Microoptoelectromechanical Micro-g Accelerometer

The paper investigates a microoptoelectromechanical accelerometer that implements optical measuring transducer built based on the optical tunneling effect. The optical transducer is a directional optical coupler that contains moving and fixed waveguides from Si
3
N
4
with dimensions of 0.3 ×1 μm. The treatise studies the normalized transmission at the directional coupler output depending on the gap and coupling length. Due to the positioning system, the optical measuring transducer can have several operating points with different optical sensitivity. For instance, for a set coupling length of 100 μm, the sensitivity of the directional coupler may reach 6.25 × 10
⁶
m
^-1
, 20 × 10
⁶
m
^-1
or 41.7 × 10
⁶
m
^-1
for initial gaps of 255, 120 and 70 nm, correspondingly. The comb-drive actuator has three independent stages with 600, 50 and 4 fingers. It allows setting a necessary gap (from 0 to 2.8 μm) between the waveguides. It also imitates microaccelerations (from 16 micro-g to 3 g) by using electrostatic forces. The study proposes a method for selecting parameters of the positioning system (electrode voltage, number of fingers, spring suspension stiffness and inertial mass).