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

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Gaafar, Mahmoud A.
Jalas, Dirk
O'Faolain, Liam
Li, Juntao
Krauss, Thomas F.
Petrov, Alexander Yu.
Eich, Manfred
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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 6Win 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 mu m wavelength which opens new possibilities for "on-chip" frequency manipulation and all-optical switching in optical telecommunications.
Optical materials and structures , Optics and photonics , Slow light
Gaafar, M. A., Jalas, D., O’Faolain, L., Li, J., Krauss, T. F., Petrov, A. Y. and Eich, M. (2018) 'Reflection from a free carrier front via an intraband indirect photonic transition', Nature Communications, 9, 1447 (10pp). doi: 10.1038/s41467-018-03862-0