  Waveguide integrated optical modulators in the mid-infrared (mid-IR) wavelength range are of significant interest for molecular spectroscopy in one hand, as on-chip synchronous detection can improve the performance of detection systems, and for free-space communications on the other hand, where optical modulators working in the atmospheric transparency windows are crucially missing. Here we report for the first time the demonstration of optical modulation in mid-IR photonic circuit reaching wavelengths larger than 8 um. Moreover, optical modulation in an unprecedented wavelength range, from 5.5 to 11 um wavelength is shown, relying on a broadband Ge-rich graded-SiGe platform. This first demonstration is used as a proof of concept, to experimentally confirm the free-carrier absorption effect modeling. These results pave the way towards efficient high-performance electrically-driven integrated optical modulators in the mid-IR wavelength range. 
Optical modulation in Ge-rich SiGe waveguides in the mid-IR wavelength   range up to 11 um