Multimode, Aperiodic Terahertz Surface-Emitting Laser Resonators

Abstract

Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric (vertically radiative but low quality factor Q) and anti-symmetric (non-radiative, high Q) modes is indeed here fully overcome, offering a concrete perspective of highly efficient vertical emitting resonators. We here exploit electrically pumped terahertz quantum cascade heterostructures to devise two-dimensional seven-fold quasi-crystal resonators, exploiting rotational order or irregularly distributed defects. By lithographically tuning the lattice quasi-periodicity and/or the hole radius of the imprinted patterns, efficient multimode surface emission with a rich sequence of spectral lines distributed over a 2.9-3.4 THz bandwidth was reached. We demonstrated multicolor emission with 67 mW of peak optical power, slope efficiencies up to «70 mW/A, 0.14% wall plug efficiencies and beam profile results of the rich quasi-crystal Fourier spectrum that, in the case of larger rotational order, can reach very low divergence.

Highly efficient surface-emitting semiconductor lasers exploiting quasi-crystalline distributed feedback photonic patterns

“…S4). The comparison clearly unveils that, in the case of multimode disordered resonators with identical dimensions, the selected Octonacci pattern leads to a 40 time increase in the slope efficiency with respect to random 39 lasers and a 11 time increase with respect to the quasi-crystal 44 lasers, with a major increase in the emitted power. Additionally, alternative single-frequency-mode 1D DFB emitters 27,28 , relying on a different concept for feedback/extraction, exhibit a power decrease of up to more than an order of magnitude and a related significant reduction in the slope efficiency, clearly highlighting the superior quantum efficiency of the quasi-crystal, tunable lasers demonstrated in the present work.…”

“…The GaAs/Al 0.15 Ga 0.85 As QCL heterostructure was grown by molecular beam epitaxy on an undoped GaAs substrate. The active region features a three-quantumwell architecture with a single extractor well 44 . The layer sequence is 5.5/11.0/1.8/11.5/3.8/9.4/4.2/18.4 (in nm), where the Al 0.15 Ga 0.85 As layers are shown in bold face, GaAs is shown in roman font, and the underlined number indicates a Si-doped layer with a density of 2 × 10 16 cm −3 .…”

“…To date, quasi-crystal lasers have been exploited in combination with THz QCL heterostructures to tailor the emission spectra, control the light feedback and outcoupling, and shape the emitted beams, exploiting either one-dimensional architectures such as Fibonacci gratings 43 or two-dimensional geometries such as a five-fold Penrose pattern 11 or a seven-fold pattern with different rotational symmetries 44 .…”

All-optical adaptive control of quantum cascade random lasers

“…Recently, quantum cascade random lasers (QCRLs) that intrinsically feature multi-mode emission [10][11][12][13][14][15] were demonstrated ( Fig. 1a).…”

Continuous-wave Highly Efficient Low-Divergence Terahertz Wire Lasers

“…The development of modern nanofabrication technologies, combined with new laser resonator concepts, have recently enabled the control and confinement of electron and photon paths in optoelectronic devices with an unprecedented degree of control. For example, microcavities 4 , photonic crystals 5,6 , and both pseudo-random 7,8 and random 9 photonic structures, can manipulate and confine light in small volumes, and at targeted frequencies. This has further expanded the functionality of the THz QCL, allowing operation at a single emission frequency 7 or over a broad (0.5 THz) frequency bandwidth, or with designed directional beam patterns 8 .…”