Abstract
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.
Highlights
Quasi-crystal structures do not present a full spatial periodicity but are constructed starting from deterministic generation rules
The 1D photonic quasi-crystal concept has been used with electrically injected THz quantum-cascade lasers (QCLs)[15], allowing surface emission at chosen angles and wavelengths from tightly-confining double-metal waveguides, the wall-plug (WP) efficiency was still poor (E0.01%)[15]
These problems have recently been addressed by engineering 1D edge-emitting third-order distributed feedback lasers (DFBs)18, 1D photonic heterostructures19,20, 2D annular DFBs21 and 2D photonic crystal lasers[22,23,24]
Summary
Quasi-crystal structures do not present a full spatial periodicity but are constructed starting from deterministic generation rules. Operation is normally achieved on modes at the edges of photonic bandgaps or on the localized states formed by suitably designed defects within the periodic photonic lattice When compared with their periodic counterparts, quasi-crystalline structures[6,7] show significant richness and flexibility in engineering specific device optical properties[8,9], like in random structures[10]. The use of double-metal waveguides offers considerable advantages for maximizing the operating temperature in THz QCLs, such devices suffer from the lack of efficient extraction and collimation of the output radiation[16,17] These problems have recently been addressed by engineering 1D edge-emitting third-order distributed feedback lasers (DFBs)18, 1D photonic heterostructures19,20, 2D annular DFBs21 and 2D photonic crystal lasers[22,23,24]. We report the development of high WP efficiency 2D photonic quasicrystal THz QCLs based on a Penrose P2 (kite and dart) tiling with a five-fold rotational symmetry[6]
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