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Phys Rev Lett. 2014 Feb 7;112(5):053904. Epub 2014 Feb 6.

Optically induced indirect photonic transitions in a slow light photonic crystal waveguide.

Author information

1
Institute of Optical and Electronic Materials, Hamburg University of Technology, Hamburg 21073, Germany.
2
SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, United Kingdom.
3
SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, United Kingdom and State Key Laboratory of Optoelectronic Materials & Technology, Sun Yat-sen University, Guangzhou 510275, China.
4
SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, United Kingdom and Department of Physics, University of York, Heslington, York, YO10 5DD, United Kingdom.

Abstract

We demonstrate indirect photonic transitions in a silicon slow light photonic crystal waveguide. The transitions are driven by an optically generated refractive index front that moves along the waveguide and interacts with a signal pulse copropagating in the structure. We experimentally confirm a theoretical model which indicates that the ratio of the frequency and wave vector shifts associated with the indirect photonic transition is identical to the propagation velocity of the refractive index front. The physical origin of the transitions achieved here is fundamentally different than in previously proposed refractive index modulation concepts with fixed temporal and spatial modulation frequencies; as here, the interaction with the refractive index front results in a Doppler-like signal frequency and wave vector shift. Consequently, the bandwidth over which perfect mode frequency and wave vector matching is achieved is not intrinsically limited by the shape of the photonic bands, and tuning of the indirect photonic transitions is possible without any need for geometrical modifications of the structure. Our device is genuinely nonreciprocal, as it provides different frequency shifts for co- and counterpropagating signal and index fronts.

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