Post processing dispersion trimming for on-chip mid-infrared supercontinuum generation

On-chip mid-infrared (3-20 μm) supercontinuum (SC) generation has potential applications in many different fields such as bio imaging, environmental sensors and security [1]. Recently, the wide transparency window from 3 to 15 μm and CMOS compatibility of germanium, along with the prediction of great nonlinear properties [2-3], have attracted a growing interest toward germanium-based platforms. In particular, silicon-germanium on silicon waveguides have been studied [4-9] and octave spanning SC generation up to 8.5 μm has been demonstrated in this platform [10]. The spectral properties and the coherence of the generated SC strongly depend on the waveguide's dispersion profile and a careful design of the group velocity dispersion is required. However, the actual dispersion of the waveguide produced by fabrication is often different from the target one, as it is sensitive to fabrication inaccuracies, surface contamination and the presence of defects. Post-process tuning mechanisms are therefore of great interest to adjust or correct a posteriori the waveguide dispersion to match the target value. Here, we experimentally show that it is possible to fine tune the dispersion profile a posteriori by adding a chalcogenide cladding layer on top of a highly nonlinear silicon-germanium on silicon waveguide, introducing a simple post processing tool to control the supercontinuum dynamics and its properties.