Advances Toward Ge/SiGe Quantum-Well Waveguide Modulators at 1.3μm

Abstract

The paper reports on the developments of Ge/SiGe quantum well (QW) waveguide modulators operating at 1.3 μm. Two modulator configurations have been studied: The first one is based on QW structures grown on a 13-μm SiGe buffer on bulk silicon. Light was directly coupled and propagated in Ge/ Si <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$_{0.35}$</tex></formula> Ge <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.65}$</tex></formula> QWs. Using a 3-μm-wide and 50-μm-long modulator, an extinction ratio (ER) up to 6 dB was obtained at 1.3 μm. In the second configuration, the aim is to integrate Ge/SiGe QW on standard silicon-on-insulator (SOI) waveguides. A reduction of buffer thickness is then required to allow the light coupling from Si waveguide to Ge/SiGe QW. To this purpose, first we demonstrated QCSE with a thin (360-nm-thick) Si <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.08}$</tex></formula> Ge <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.92}$</tex></formula> buffer on silicon using the well-known Ge/Si <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.15}$</tex></formula> Ge <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.85}$</tex> </formula> QWs (operated at a wavelength of 1.4 μm). Based on these promising experimental results, we theoretically investigated properties of a Ge/Si <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.65}$</tex></formula> Ge <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$_{0.35}$</tex></formula> QW modulator integrated on SOI waveguides. 7.7 dB ER were predicted with 4 dB optical insertion loss and an estimated energy consumption of 59 fJ/bit for a modulator length as short as 69 μm.