Speaker: Prof. Joerg Schilling, Professor, Martin-Luther-University Halle-Wittenberg, Germany.

Title: "Creating a second-order nonlinearity by breaking symmetry: The hunt for (2) in 
        silicon photonics"

Date: Wednesday, 8th July 2026 - Time: 4 PM

Hi-Tea & Coffee: 5 PM
Venue: CeNSE Seminar Hall

Abstract:

Second-order nonlinear processes like sum- and difference frequency generation form the heart 
of efficient all-optical frequency transformation in optics and photonics. They are used to 
build optical parametric amplifiers and oscillators as well as create entangled photon pairs 
via spontaneous downconversion for optical quantum computing and quantum communications. 
In all of these processes, the second-order susceptibility c(2) represents the crucial parameter. 
Unfortunately, the large class of centrosymmetric and amorphous materials, including Si, SiO2 
and Si3N4 lack a dipolar c(2), so that efficient c(2)-related nonlinear processes seemed to 
be impossible in integrated silicon photonics.

In this talk, firstly, an overview of attempts to introduce a c(2)in silicon by breaking the symmetry 
of its crystal lattice by applying inhomogeneous mechanical stress is given. These studies ultimately 
led to the investigation of electric field-induced second-order nonlinearity in silicon and 
silicon-based amorphous materials like silicon-rich nitride (SiNx) and silicon-rich oxide (SiOx). 
Investigating electric-field-induced second harmonic generation (EFISH) in these materials showed 
that an effective or quasi-c(2) as a product of the natural c(3) and the applied dc-field can be induced. 
Values of c(2)quasi » 60pm/V exceeding the c(2) of classic nonlinear crystals like LiNbO3 could be demonstrated. 
By tuning the silicon content in these films to optimise the material c(3) and the breakdown field, 
even values on the order of c(2)quasi =100pm/V are predicted. Since the material can be structured 
using classic CMOS processes, the design of optical resonators or quasi-bound states in the continuum 
(quasi-BIC)  is possible, thus leading to a further increase in the efficiency of the nonlinear processes 
by strong confinement of the light. Overall, the electric-field-induced generation of an effective c(2) 
allows for the creation and control of the second-order nonlinearity by design, offering a large 
flexibility for active nonlinear processes in integrated Si photonics in the future.

Biography:
Joerg Schilling studied physics at the Martin-Luther-University (MLU) Halle-Wittenberg (Germany). 
Subsequently, he was awarded a PhD in Physics for his research at the Max-Planck-Institute of Microstructure 
Physics on 2D- and 3D photonic crystals based on macroporous silicon in 2002 under the supervision of 
Prof. Ulrich Goesele. After a 3 year Postdoc at California Institute of Technology in the group of 
Prof. Axel Scherrer, he was awarded a Royal Society University Research Fellowship and moved to Queen’s 
University Belfast, undertaking research in hyperbolic metamaterials. In 2009, he became a Junior Research 
Group leader at the Centre for Innovation Competence SiLi-nano at the MLU in Halle (Germany) and subsequently 
obtained a  Full Professorship in 2017, doing research in the area of active silicon and hybrid photonics. 
His recent research focuses on emission enhancement of Ge-quantum dots and Si-nanocrystals using Mie 
resonances and the use of electric field-induced second-order nonlinearity for frequency 
transformation processes.

Host Faculty:  Prof. Pavan Nukala