Design of silicon photonics based accelerometer for displacement sensing applications

In this work, we investigate an optical accelerometer utilizing single-mode Si/SiO2 waveguides at 1550 nm as a displacement sensing unit. The device is based on quad beam configuration, made of a fixed frame and a mass, moving within a limited range along vertical direction. Three straight Si/SiO2 waveguides are placed aligned along the central axes of the accelerometer, two on both ends on the frame and one on the mass, such that the displacement of mass leads to a drop of the coupled light intensity. When the mass is at rest, the intensity of the guided mode is at its highest value. Acceleration is then measured by monitoring the intensity modulation. Lateral dimensions of the waveguides are similar, where the height and width are 200 nm and 500 nm, respectively. The effective index of single mode Si/SiO2 waveguides (neff = 2.3550 at 1550 nm) is calculated using Finite Difference Eigenmode (FDE) method. The field profile of fundamental TE mode is to a good approximation given by Gaussian field distribution. The correlation of guided light intensity and the mass displacement was obtained numerically using mode-coupling theory. We show that our configuration is highly sensitive, drastic intensity drop (100 dB) happens at mass-frame misalignment within ±7 μm and displacement by 3 μm causes intensity decrease of 10.8 dB. Thus, design of CMOS-compatible miniature silicon photonic accelerometers with inherent properties such as multiplexability and immunity to external electro-magnetic fields are promising candidates for low cost real-time vibration monitoring sensors applicable in harsh environments.