Photonic quasi-crystal terahertz lasers

• Published in: Nature communications Vol. 5; no. 1; p. 5884
• Main Authors: Vitiello, Miriam Serena, Nobile, Michele, Ronzani, Alberto, Tredicucci, Alessandro, Castellano, Fabrizio, Talora, Valerio, Li, Lianhe, Linfield, Edmund H., Davies, A. Giles
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.12.2014; Nature Publishing Group; Nature Pub. Group
• Subjects: 639/301/1019/1020; 639/301/1019/1022; 639/624/400/561; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms6884

Quasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of ‘defects’, which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser; specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1–0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum. Various vertical surface emitting, terahertz quantum-cascade lasers have been proposed recently but these suffer from power cancellations in the far-field and limited extraction efficiencies. Here, Vitiello et al. circumvent these issues using two-dimensional photonic quasi-crystalline resonators.