Ultrathin Silicon-on-Insulator Grating Couplers

Abstract

We demonstrate a novel grating coupler fabricated on a silicon-on-insulator (SOI) wafer operating at 1550 nm, based on an ultrathin 50-nm silicon geometry. The devices are fabricated in a CMOS-compatible process with a single etch step. A low insertion loss of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 3.7}~{\rm dB}$</tex></formula> is achieved. We also calculate the backreflection loss to be <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 14}~{\rm dB}$</tex></formula> . The devices are likely to be useful in terms of light coupling between optical fibers and ultrathin silicon waveguides.