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Ultrafast All Optical Switching of Photonic Crystals |
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Written by Ilya Fushman
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Tuesday, 23 January 2007 |
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20 GHz All Optical Modulation :
We have been able to modulate Photonic crystal cavities at rates on the order of 20 to 100 gigahertz, and pulse powers around 70 picojoules. This is potentially a promising technology for all optical data manipulation. On the right you see the theoretical prediction of the signal modulation for this experiment.
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 Photonic Crystal Cavity modulated by Free Carriers that are injected into the GaAs via an aboveband pump. The Carrier lifetime is strongly reduced due to the large surface area to volume ratio in the photonic crystal.
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Experimental Result:
The experimental result closely follows the theory. The cavity is shifted by approximately one linewidth. While this does not look like a large shift, it actually is, considering that the linewidth of this cavity is quite broad. The shift is only dependent on the number of generated carriers.
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Limitations:
As noted, this shift is proportional to the injected photon number, and the extinction depends on the cavity linewidth. In principle, the maximum shift corresponds to every atom in the semiconductor donating an electron to the Free Carrier gas, which would be about 1022-1023 cm-3 carriers. This would lead to an index shift that is much larger than the one in this paper, generated with ~1019 cm-3 carriers. We could shift the cavity by a huge amount. However, pulse energies corresponding to more than 1020 cm-3 carriers lead to melting of GaAs, and permanently destroy the cavity. So the maximal acceptable shift is approximately 10-3 of the value for GaAs.
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You can find the preprint of this article here:
http://arxiv.org/abs/physics/0611303
or download the attached PDF file here:
Ultrafast Nonlinear Tuning of Photonic Crystal Cavities ( 2007-03-02 11:22)
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Last Updated ( Tuesday, 14 August 2007 )
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