Trento, Italy--An article in Nature Materials at www.nature.com/nmat/journal/vaop/ncurrent/full/nmat3200.html describes the very first observation of second harmonic generation (SHG) in a strained silicon waveguide. Even though silicon is a centrosymmetric material that prevents second order nonlinearities, Italian collaborators led by professor Lorenzo Pavesi at the University of Trento succeeded in deforming the silicon structure with a stressing silicon nitride overlayer and were able to demonstrate the rise of significant second-order optical nonlinearities as big as those observed in widely diffused second-order lithium niobate materials.
The researchers say that nonlinear silicon photonics was until now founded on high-order nonlinear effects, which require a very high optical power. But now, second-order nonlinear activity considerably lowers the power threshold and allows silicon to enter the realm of nonlinear crystals, where direct nonlinear down-conversion or other optical parametric processes can be achieved. All the ingredients to get mid-infrared (mid-IR) or far-infrared (far-IR) parametric optical sources are now available and the race to demonstrate such exciting possibilities is open.
This SHG observation could open the mid-IR and far-IR spectral regions to low-cost, mass-produced, integrated optical sources. In addition, electrooptical effects that lead to low power and extremely fast optical modulators and switches can be engineered in silicon photonics.
The collaboration involved researchers from the University of Trento, Bruno Kessler Foundation, University of Modena & Reggio Emilia, University of Brescia, and from the CIVEN-consortium.
SOURCE: University of Trento