Indirect photonic transitions for light control in integrated photonics
Final Report Abstract
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 were 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 employed 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. The obtained transition is not symmetric and the signal interacting with the front from the other side experiences a different transition. 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. Nonlinear degenerate four wave mixing and cross phase modulation are established approaches for all optical frequency manipulation in a silicon chip. These approaches require exact group velocity and/or phase velocity matching of pump, signal and idler. On the other hand, frequency manipulation of light by a free carrier front propagating in a silicon waveguide has important advantages for frequency manipulation on chip. It requires no phase velocity matching, is not dependent on the shape and duration of the pump pulse and allows packet switching. Furthermore, the indirect intraband transition with forward reflection has another important advantage over all other frequency shifting mechanisms. At sufficient pump power the complete transition is achieved which is defined by the unperturbed band and group velocity of the front only. The perturbed band does not influence the transition any more. Thus the frequency shift becomes independent of the pump power.
Publications
- “Free carrier front induced indirect photonic transitions: a new paradigm for frequency manipulation on chip”, ACS Photonics 4, 2751 (2017)
M. A. Gaafar, A. Yu. Petrov, and M. Eich
(See online at https://doi.org/10.1021/acsphotonics.7b00750) - “Transmission and reflection from a free carrier front in a silicon slow light waveguide”, Asia Communications and Photonics Conference, OSA Technical Digest, S4D. 2 (2017)
M. A. Gaafar, D. Jalas, L. O’Faolain, J. Li, T. F. Krauss, A. Yu. Petrov, M. Eich
(See online at https://doi.org/10.1364/ACPC.2017.S4D.2) - “Indirect transitions at a free carrier front in a silicon slow light waveguide”, Advanced Photonics 2018, OSA Technical Digest NpM4I. 7 (2018)
A. Yu. Petrov, M. A. Gaafar, D. Jalas, L. O’Faolain, J. Li, T. F. Krauss, M. Eich
(See online at https://doi.org/10.1364/NP.2018.NpM4I.7) - “Reflection from a free carrier front via an intraband indirect photonic transition”, Nature Communications 9, 1447 (2018)
M. A. Gaafar, D. Jalas, L. O’Faolain, J. Li, T. F. Krauss, A. Yu. Petrov, M. Eich
(See online at https://doi.org/10.1038/s41467-018-03862-0)
