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Mid-infrared integrated photonics with Ge quantum wells.
Frigerio J., Barzaghi A., Falcone V., Calcaterra S., Giani R., Ballabio A., Isella G., Chrastina D., Ortolani M., Virgilio M.
In recent years, mid-infrared (MIR) integrated photonics has raised an increasing interest due to the envisioned applications in molecular sensing, environmental monitoring and security. Nowadays, MIR photonics based on the silicon-on-insulator platform, working up to $3.2 \mu m$ has already reached a high technology readiness level. Nevertheless, extending the operational wavelength toward the long-wave-infrared (LWIR) is still challenging and key functionalities such as photodetection, high-speed modulation and wavelength conversion are still not available. In this framework, Ge/SiGe quantum wells could be exploited to fill the gap. Intersubband optical transitions in the valence band of such heterostructures can be used for light detection, for high-speed modulation through the quantum confined Stark effect (QCSE), and for wavelength conversion through second-harmonic generation. Ge/SiGe QWs can be easily grown on top of SiGe buffers, making them fully compatible with the existing SiGe-on-Si material platform. In this contribution, we show an experimental demonstration of second-harmonic generation and a preliminary study for the realization of integrated modulators and photodetectors.