Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics
Artikel i vetenskaplig tidskrift, 2021

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


nonlinear optics

silicon photonics


quantum wells


Jacopo Frigerio

Politecnico di Milano

Chiara Ciano

Universita degli studi - Roma Tre

Joel Kuttruff

Universität Konstanz

Andrea Mancini

Sapienza, Università di Roma

Ludwig-Maximilians-Universität München (LMU)

Andrea Ballabio

Politecnico di Milano

Daniel Chrastina

Politecnico di Milano

Virginia Falcone

Politecnico di Milano

Monica De Seta

Universita degli studi - Roma Tre

L. Baldassarre

Sapienza, Università di Roma

Jonas Allerbeck

Université du Luxembourg

Universität Konstanz

Daniele Brida

Université du Luxembourg

Lunjie Zeng

Chalmers, Fysik, Nano- och biofysik

Eva Olsson

Chalmers, Fysik, Nano- och biofysik

Michele Virgilio

Universita di Pisa

M. Ortolani

Sapienza, Università di Roma

ACS Photonics

2330-4022 (eISSN)

Vol. 8 12 3573-3582


Nanovetenskap och nanoteknik


Atom- och molekylfysik och optik

Annan fysik

Den kondenserade materiens fysik


Chalmers materialanalyslaboratorium



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