Influence of discontinuities on photonic waveguides

Abstract

Fabrication-induced imperfections in photonic wire waveguides, such as roughness, stitching errors, and discontinuities, degrade their performance and thereby lower the yield of large-scale systems. This degradation is primarily due to the high insertion losses induced by imperfections, which scale nonlinearly with the index contrast in wire waveguides. Here we investigate the influence of discontinuities in photonic waveguides and later show a platform that is robust to fabrication imperfections. Our platform is based on an array of silicon nano-pillars, arranged to form a sub-wavelength (SW) grating waveguide. We focus on investigating the robustness by considering an abrupt break in the waveguide, as an extreme case of discontinuity. We show that sub-wavelength silicon waveguides are robust against unwanted large discontinuities relative to the operating wavelength. We measure a transmission loss of <2.2 dB at 1550 nm, for a discontinuity of length 2.1 μm, when compared to more than 7 dB of loss in conventional silicon wire waveguides for the same discontinuity. Our results show that this mode of protection is broadband, covering the entire telecommunication band (λ =1500–1600 nm). We believe that this investigation of the influence of discontinuities in photonic waveguides could be a step toward the realization of low-loss optical waveguides.