Abstract-Theory of low-power ultra-broadband terahertz sideband generation in bi-layer graphene

• J. A. Crosse,
• Xiaodong Xu,
• Mark S. Sherwin
• & R. B. Liu

• Affiliations
• Contributions
• Corresponding author

http://www.nature.com/ncomms/2014/140924/ncomms5854/abs/ncomms5854.html

Nature Communications

 

5,

 

Article number:

 

4854

 

doi:10.1038/ncomms5854

Received

 

18 January 2014 

Accepted

 

30 July 2014 

Published

 

24 September 2014

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In a semiconductor illuminated by a strong terahertz (THz) field, optically excited electron–hole pairs can recombine to emit light in a broad frequency comb evenly spaced by twice the THz frequency. Such high-order THz sideband generation is of interest both as an example of extreme nonlinear optics and also as a method for ultrafast electro-optical modulation. So far, this phenomenon has only been observed with large field strengths (~10 kV cm⁻¹), an obstacle for technological applications. Here we predict that bi-layer graphene generates high-order sidebands at much weaker THz fields. We find that a THz field of strength 1 kV cm⁻¹ can produce a high-sideband spectrum of about 30 THz, 100 times broader than in ​GaAs. The sidebands are generated despite the absence of classical collisions, with the quantum coherence of the electron–hole pairs enabling recombination. These remarkable features lower the barrier to desktop electro-optical modulation at THz frequencies, facilitating ultrafast optical communications.