A low mode confinement integrated waveguide platform for high resolution displacement sensing

We demonstrate an integrated waveguide technology and apply it to displacement sensing. The waveguide consists of a 175 nm thick Si3N₄ core layer with a 3,000 nm SiO₂ bottom cladding and exhibits a large evanescent field. Although the nanophotonic waveguides feature sub-X/4 vertical confinement, they are fabrication tolerant with micron-scale lateral features. The technology enables complex photonic circuits without electron-beam lithography, which is commonly required for silicon nanophotonics. An unbalanced Mach-Zehnder interferometer is demonstrated in which the presence of an optical fiber near the waveguide surface induces a phase shift, which correlates with the fiber´s position. We discuss future work and prospects for high-resolution displacement sensing.