In-plane degree of freedom optical waveguide displacement sensors based on geometrical modulation

Abstract

Suspended optical waveguide displacement sensors (SOWDS) technology is presented. The sensors are based on optical modulation in the form of energy losses and mode conversions, resulting from relative displacement of aligned and suspended waveguides. The building block of the suspended waveguides is a single-crystal silicon (SCS) beam with top superficial layers comprising 0.6-μm-thick SiO 2, 0.4-μm-thick Si 3N 4, and 0.6-μm-thick SiO 2. The SCS has a typical cross section of 1.6 μm × 10 μm and may guide light with wavelengths in the 1.3–1.5 μm range. The first SiO 2 layer serves as a buffer layer that allows light with wavelength in the range 0.6–0.9 μm to be guided in the Si 3N 4 layer. This paper discusses the theoretical considerations, the fabrication process, and the characterizations of fixed—free and fixed—fixed SOWDS configurations. Although the main purpose of the technology is for displacement sensing (e.g., acoustical, vibrational, flow, thermal, etc.), it is considered as an independent displacement sensing means for actuators.