Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics

Second-harmonic generation (SHG) is a direct measure of the strength second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however, silicon-foundry compatible group IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration nonlinearity silicon photonics platforms. Here we demonstrate strong Ge-rich quantum wells grown on Si wafers. Unlike Si-rich epilayers, epilayers allow for waveguiding substrate. The breaking artificially realized pair asymmetric coupled (ACQW), three quantum-confined states equidistant energy, resulting double resonance SHG. Laser spectroscopy experiments giant at mid-infrared pump wavelengths between 9 12 ?m. Leveraging intersubband dipoles, susceptibility ?(2) almost reaches 105 pm/V, 4 orders magnitude larger than bulk which, by Miller’s rule, range 10 pm/V norm.