Abstract
Silicon is not an electro-optic material by itself but the required second-order optical nonlinearity can be induced by breaking the inversion symmetry of the crystal lattice. Recently, an attractive approach has been demonstrated based on a surface-activation in a CMOS-compatible HBr dry etching process. In this work, we further investigate and quantify the second-order nonlinearity induced by this process. Using THz near-field probing we demonstrate that this simple and versatile process can be applied to locally equip silicon nanophotonic chips with micro-scale areas of electro-optic activity. The realization of a first fully integrated Mach-Zehnder modulator device - based on this process - is applied to quantify the nonlinearity to an effective χ((2)) of 9 ± 1 pm/V. Analysis of the thermal stability of the induced nonlinearity reveals post-processing limitations and paths for further efficiency improvements.
Highlights
Using THz near-field probing we demonstrate that this simple and versatile process can be applied to locally equip silicon nanophotonic chips with micro-scale areas of electro-optic activity
Driven by the ongoing demand for higher bandwidth and cost reduction silicon photonics has seen a rapid development in recent years as an important platform for CMOS-compatible integrated optical devices [1,2]
We have shown that a very simple CMOS-compatible process based on an HBr plasma-mediated chemical surface treatment, in the following denoted as plasma-activation (PA) is a promising alternative to induce secondorder nonlinearity in silicon nanophotonic waveguides [13]
Summary
Driven by the ongoing demand for higher bandwidth and cost reduction silicon photonics has seen a rapid development in recent years as an important platform for CMOS-compatible integrated optical devices [1,2]. The evanescent field of a propagating guided mode in such a structure interacts with the nonlinear active cladding and generates an effective second-order nonlinearity [5,6,7,8,9] Alternative to such hybrid approaches another basically different solution is to break the centrosymmetry of the silicon lattice itself by strain [10,11,12]. A record value of strain-induced nonlinearity χ(2) of 190 pm/V has been achieved recently by Chmielak et al by directly attaching silicon nitride straining layers on small cross-section silicon rib-waveguides [11,12] These results are very promising still an unanswered question is how to implement these solutions into CMOS-compatible process lines and how to limit an induced electro-optic activity to dedicated chip areas. The modulator is based on an asymmetric MachZehnder interferometer and utilized for the quantification of the achieved effective secondorder nonlinearity
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