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

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_0.35Ge_0.65 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_0.08Ge_0.92 buffer on silicon using the well-known Ge/Si_0.15Ge_0.85 QWs (operated at a wavelength of 1.4 μm). Based on these promising experimental results, we theoretically investigated properties of a Ge/Si_0.65Ge_0.35 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.