A Guided-Mode-Selective Focusing Grating Coupler

Abstract

Guided-mode-selective focusing grating coupler, which couples out not TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode but TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode to a free space wave, was designed at around 850-nm wavelength for constructing a wavelength-division-multiplexing chip-to-chip optical interconnection board. The coupler was fabricated in a slab waveguide consisting of a Ge-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> main-guiding core, a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> subguiding core, a Si-N grating layer, and a high-reflection layer. Coupling efficiencies for TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> modes were obtained to be 5% and 46%, respectively, with 0.1-mm interaction length. The focus spot size of 3×1 μm was obtained for TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode.