A novel nano-mechanical displacement detection based on a photonic nanowire waveguides coupler

Abstract

Microoptoelectromechanical systems (MOEMS) are promising choices in achieving compact and yet precise sensors with intensity / phase modulation techniques or resonance shift based techniques. Particularly in the area of displacement sensing, MOEMS device may potentially offer a high accuracy and yet compact solution for highly sensitive portable sensors. We propose a novel approach of a hybrid device consisting of nano-mechanical structures and nanowire silicon photonics to achieve a new displacement sensing mechanism that does not require segmentization or intersecting of waveguides. In this work, we demonstrate that by optimizing a relatively broadband air-suspended nanowire waveguide directional coupler design that is integrated using silicon photonics structures, we can achieve sufficient attenuation without the need of waveguide segmentization thus effectively reducing the undesired insertion and coupling losses. First, we numerically design and optimize, utilizing a 3D FDTD numerical method, a nanowire waveguide directional coupler that is capable of achieving a -13 dB extinction ratio at submicron displacements. Next, we fabricate the proposed nanowire photonic waveguide directional coupler utilizing a simple and monolithic fabrication approach. The nano-mechanical structures are then characterized and calibrated in-situ under a scanning electron microscopy (SEM). The optical sensitivities of the waveguide directional couplers are then characterized on a vibration isolation optical table under low noise conditions. The noise spectrum densities are also characterized by driving the structures under an AC actuating voltages to understand the minimum detectable nano-displacements. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).