Reflection from a free carrier front via an intraband indirect photonic transition

Mahmoud A. Gaafar, Hamburg University of Technology
Dirk Jalas, Hamburg University of Technology
Liam O'Faolain, University of St Andrews
Juntao Li, Sun Yat-Sen University
Thomas F. Krauss, University of York
Alexander Yu Petrov, Hamburg University of Technology
Manfred Eich, Hamburg University of Technology


© 2018 The Author(s). The reflection of light from moving boundaries is of interest both fundamentally and for applications in frequency conversion, but typically requires high pump power. By using a dispersion-engineered silicon photonic crystal waveguide, we are able to achieve a propagating free carrier front with only a moderate on-chip peak power of 6 W in a 6 ps-long pump pulse. We employ an intraband indirect photonic transition of a co-propagating probe, whereby the probe practically escapes from the front in the forward direction. This forward reflection has up to 35% efficiency and it is accompanied by a strong frequency upshift, which significantly exceeds that expected from the refractive index change and which is a function of group velocity, waveguide dispersion and pump power. Pump, probe and shifted probe all are around 1.5 μm wavelength which opens new possibilities for "on-chip" frequency manipulation and all-optical switching in optical telecommunications.