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Sci Rep. 2015 Nov 9;5:16207. doi: 10.1038/srep16207.

Photo-generated metamaterials induce modulation of CW terahertz quantum cascade lasers.

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Dipartimento Interateneo di Fisica, Università degli Studi e Politecnico di Bari, via Amendola 173, I-70126 Bari Italy.
CNR-IFN UOS Bari, via Amendola 173, I-70126 Bari Italy.
Dipartimento di Scienza e Alta Tecnologia, Università dell'Insubria, via Valleggio 11, I-22100 Como Italy.
CNR-SPIN, via Vetoio 10, I-67100 L'Aquila Italy.
NEST, CNR - Istituto Nanoscienze and Scuola Normale Superiore, piazza San Silvestro 12, I-56127 Pisa Italy.


Periodic patterns of photo-excited carriers on a semiconductor surface profoundly modifies its effective permittivity, creating a stationary all-optical quasi-metallic metamaterial. Intriguingly, one can tailor its artificial birefringence to modulate with unprecedented degrees of freedom both the amplitude and phase of a quantum cascade laser (QCL) subject to optical feedback from such an anisotropic reflector. Here, we conceive and devise a reconfigurable photo-designed Terahertz (THz) modulator and exploit it in a proof-of-concept experiment to control the emission properties of THz QCLs. Photo-exciting sub-wavelength metastructures on silicon, we induce polarization-dependent changes in the intra-cavity THz field, that can be probed by monitoring the voltage across the QCL terminals. This inherently flexible approach promises groundbreaking impact on THz photonics applications, including THz phase modulators, fast switches, and active hyperbolic media.

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