Abstract-Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage

Y. J. Han, L. H. Li, A. Grier, L. Chen, A. Valavanis, J. Zhu, J. R. Freeman, N. Isac, R. Colombelli, P. Dean, A. G. Davies, and E. H. Linfield

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-25-28583

We report an extraction-controlled terahertz (THz)-frequency quantum cascade laser design in which a diagonal LO-phonon scattering process is used to achieve efficient current injection into the upper laser level of each period and simultaneously extract electrons from the adjacent period. The effects of the diagonality of the radiative transition are investigated, and a design with a scaled oscillator strength of 0.45 is shown experimentally to provide the highest temperature performance. A 3.3 THz device processed into a double-metal waveguide configuration operated up to 123 K in pulsed mode, with a threshold current density of 1.3 kA/cm2 at 10 K. The QCL structures are modeled using an extended density matrix approach, and the large threshold current is attributed to parasitic current paths associated with the upper laser levels. The simplicity of this design makes it an ideal platform to investigate the scattering injection process.

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Abstract-Hybrid electronic-photonic subwavelength cavities operating at terahertz frequencies

http://prb.aps.org/abstract/PRB/v87/i4/e041408

E. Strupiechonski¹, G. Xu¹, P. Cavalié², N. Isac¹, S. Dhillon², J. Tignon², G. Beaudoin³, I. Sagnes³, A. Degiron^1,*, and R. Colombelli^1,† 
1Institut d’Electronique Fondamentale, Université Paris Sud and CNRS, UMR8622, 91405 Orsay, France
²Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
³Laboratoire de Photonique et Nanostructures, CNRS UPR20, 91460 Marcoussis, France

We report on the concept and realization of terahertz (THz) metallic/semiconductor cavities characterized by dimensions as small as λ_eff/9 in all directions of space (or λ/30 with the vacuum wavelength). We experimentally prove that the capacitance and inductance of these devices are not interdependent, as in purely photonic cavities, but that they can be adjusted almost independently, as in an electronic circuit. This functionality proves that the dimensions of these hybrid electronic-photonic devices are intrinsically not limited by diffraction as in conventional photonic resonators. Using arguments from transmission line theory, we show that it is necessary to include at least one metallic loop in the cavity design to access this regime and we note, as a corollary, that some recent proposals to miniaturize THz resonators and devices beyond the diffraction limit do not meet this fundamental requirement. Our results shed a light on the ability to describe THz/metallic cavities in terms of circuit elements. Furthermore, upon insertion of electrical contacts, these extremely subwavelength resonators can potentially lead to advances in THz detectors and phased array antennas.

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