Mid-infrared second harmonic generation in p-type Ge/SiGe quantum wells: Toward waveguide integration

In this work we investigate a structure based on p-doped Ge/SiGe asymmetric-coupled quantum wells (ACQW) that enables the second harmonic generation in SiGe waveguide by double-resonant intersubband transitions (ISBTs). These transitions lead to χ⁽²⁾ coefficients in the range 10⁴-10⁵ pm/V, significantly higher compared to the one of conventional nonlinear materials. We developed a model for the integration of Quantum Wells (QWs) into the active region of the waveguide through an adiabatic taper. Furthermore, we modelled the second harmonic (SH) conversion efficiency as a function of the propagation length, under both non-phase matching and phase-matching conditions. Our work demonstrates that the SiGe ACQWs can be used in spectral ranges not covered by the majority of conventional non-linear crystals, while allowing for the ready-integration with the CMOS technologies.