Abstract-Line-defect photonic crystal terahertz quantum cascade laser

Journal of Applied Physics

A. Klimont, A. Ottomaniello,  R. Degl’Innocenti, L. Masini, F. Bianco, Y. Wu1,  Y. D. Shah, Y. Ren, D. S. Jessop,  A. Tredicucci, H. E. Beere,  D. A. Ritchie.

Scanning electron microscope (SEM) pictures of the line defect QCLs after reactive ion etching for three different line-defect waveguides. Figure (a) corresponds to D1, where the defects before BCB planarization are separated by one row of small pillars in the triangular PhC lattice. Figure (b) (D3) and (c) (D5) correspond to line-defect QCLs separated by three rows and five rows of small pillars, respectively. Figure (d) shows in more detail the defect area and identifies the main parameters of the PhC structure, such as the vectors on the direct triangular lattice, a1 and a2, the radius of the regular and defect pillars, r and R, respectively, as well as the line orientation. Figure (e) shows a typical line-defect QCL after the BCB planarization, leaving only the tops of ∼14 μm-tall pillars exposed.

https://aip.scitation.org/doi/full/10.1063/1.5120025

The terahertz (THz) quantum cascade laser (QCL) provides a versatile tool in a plethora of applications ranging from spectroscopy to astronomy and communications. In many of these fields, compactness, single mode frequency emission, and low threshold are highly desirable. The proposed approach, based on line defects in a photonic crystal (PhC) matrix, addresses all these features while offering unprecedented capabilities in terms of flexibility, light waveguiding, and emission directionality. Nine line-defect QCLs were realized in a triangular lattice of pillars fabricated in the laser active region (AR), centered around ∼2 THz by tuning the photonic design. A maximal 36% threshold reduction was recorded for these ultraflat dispersion line-defect QCLs in comparison to standard metal-metal QCL. The mode selectivity is an intrinsic property of the chosen fabrication design and has been achieved by lithographically scaling the dimension of the defect pillars and by acting on the PhC parameters in order to match the AR emission bandwidth. The measured line-defect QCLs emitted preferentially in the single frequency mode in the propagation direction throughout the entire dynamic range. An integrated active platform with multiple directional outputs was also fabricated as proof-of-principle to demonstrate the potential of this approach. The presented results pave the way for integrated circuitry operating in the THz regime and for fundamental studies on microcavity lasers.

Abstract-Hyperuniform disordered terahertz quantum cascade laser

R. Degl’Innocenti

, Y. D. Shah

, L. Masini

, A. Ronzani

, A. Pitanti

, Y. Ren

, D. S. Jessop

, A. Tredicucci

, H. E. Beere

 & D. A. Ritchie

• Scientific Reports 6, Article number: 19325 (2016)
• doi:10.1038/srep19325
• http://www.nature.com/articles/srep19325

Laser cavities have been realized in various different photonic systems. One of the forefront research fields regards the investigation of the physics of amplifying random optical media. The random laser is a fascinating concept because, further to the fundamental research investigating light transport into complex media, it allows us to obtain non-conventional spectral distribution and angular beam emission patterns not achievable with conventional approaches. Even more intriguing is the possibility to engineer a priori the optical properties of a disordered distribution in an amplifying medium. We demonstrate here the realization of a terahertz quantum cascade laser in an isotropic hyperuniform disordered distribution exhibiting unique features, such as the presence of a photonic band gap, low threshold current density, unconventional angular emission and optical bistability.

Abstract-Terahertz detection by epitaxial-graphene field-effect-transistors on silicon carbide

F. Bianco^1,a), D. Perenzoni², D. Convertino³, S. L. De Bonis^1,b), D. Spirito^1,c),M. Perenzoni², C. Coletti³, M. S. Vitiello¹ and A. Tredicucci^2,4
 HIDE AFFILIATIONS
1 NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy
2 Fondazione Bruno Kessler (FBK), Via Sommarive 18, 38123 Povo, Trento, Italy
3 CNI@NEST, Istituto Italiano di Tecnologia, Piazza S. Silvestro 12, 56127 Pisa, Italy
4 NEST, Istituto Nanoscienze-CNR and Dipartimento di Fisica “E. Fermi”, Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
a) Author to whom correspondence should be addressed. Electronic mail: federicabianco82@gmail.com
b) Present address: ICFO, Av. Carl Friedrich Gauss, Centre d'Investigació en Nanociència, Castelldefels, Barcelona 08860, Spain.
c) Present address: Istituto Italiano di Tecnologia, Nanochemistry department and Graphene labs, Via Morego 30, 16163 Genova, Italy.
Appl. Phys. Lett. 107, 131104 (2015); http://dx.doi.org/10.1063/1.4932091

http://scitation.aip.org/content/aip/journal/apl/107/13/10.1063/1.4932091?TRACK=RSS

We report on room temperature detection of terahertz radiation by means of antenna-coupledfield effect transistors (FETs) fabricated using epitaxial graphene grown on silicon carbide. The achieved photoresponsivity (∼0.25 V/W) and noise equivalent power (∼80 nW/ Hz−−−√ ) result from the combined effect of two independent detection mechanisms: over-damped plasma wave rectification and thermoelectric effects, the latter ascribed to the presence of carrier density junctions along the FET channel. The calculated plasmonic and thermoelectric response reproduces qualitatively well the measured photovoltages; the experimentally observed sign-switch demonstrates the stronger contribution of plasmonic detection compared to the thermoelectric one. These results unveil the potential of plasmonic detectors exploitingepitaxial graphene on silicon carbide for fast large area imaging of macroscopic samples.

Abstract-Terahertz photodetectors based on tapered semiconductor nanowires

L. Romeo¹, D. Coquillat², E. Husanu¹, D. Ercolani¹, A. Tredicucci³, F. Beltram¹, L. Sorba¹, W. Knap² and M. S. Vitiello^1,a)
 HIDE AFFILIATIONS
1 NEST, Scuola Normale Superiore and CNR—Istituto Nanoscienze, Piazza San Silvestro 12, I-56127 Pisa, Italy
2 Laboratoire Charles Coulomb, UMR 5221 CNRS-Universite' Montpellier 2, 34095 Montpellier, France
3 Dipartimento di Fisica, Università di Pisa, Largo Pontecorvo 3 and NEST, CNR - Istituto Nanoscienze, 56127 Pisa, Italy
a) miriam.vitiello@sns.it
Appl. Phys. Lett. 105, 231112 (2014); http://dx.doi.org/10.1063/1.4903473

http://scitation.aip.org/content/aip/journal/apl/105/23/10.1063/1.4903473?showFTTab=true&containerItemId=content/aip/journal/apl

We report on the demonstration of Terahertz (THz) broadband detectors based on field effect transistors exploiting tapered semiconductor nanowires. The intrinsic asymmetry provided by the nanowires geometry allows to achieve responsivity values as high as 55 V/W (2.5 mA/W) and a noise-equivalent-power of 3 × 10⁻¹⁰ W/Hz^1/2 independent of the specific gate voltage applied. The possibility to reduce the number of terminals required to the source and drain contacts only and the technological feasibility of multi-pixel arrays are promising for the realization of compact and integrated THz matrix array detection systems.

Abstract-Graphene field-effect transistors as room-temperature terahertz detectors

http://graphenetimes.com/2012/09/graphene-field-effect-transistors-as-room-temperature-terahertz-detectors-2/

Authors: L. Vicarelli, M. S. Vitiello, D. Coquillat, A. Lombardo, A. C. Ferrari, W. Knap, M. Polini, V. Pellegrini A. Tredicucci

The unique optoelectronic properties of graphene make it an ideal platform for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic modules, optical modulators, plasmonic devices, microcavities, and ultra-fast lasers. Owing to its high carrier mobility, gapless spectrum and frequency-independent absorption, graphene is a very promising material for the development of detectors and modulators operating in the terahertz region of the electromagnetic spectrum (wavelengths in the hundreds of micrometres), still severely lacking in terms of solid-state devices. Here we demonstrate terahertz detectors based on antenna-coupled graphene field-effect transistors. These exploit the nonlinear response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature operation at 0.3 THz, showing that our devices can already be used in realistic settings, enabling large-area, fast imaging of macroscopic samples.

Nature Materials. doi:10.1038/nmat3417

Abstract Phase-locking to a free-space terahertz comb for metrological-grade terahertz lasers

http://www.nature.com/ncomms/journal/v3/n9/abs/ncomms2048.html

• L. Consolino,
• A. Taschin,
• P. Bartolini,
• S. Bartalini,
• P. Cancio,
• A. Tredicucci,
• H. E. Beere,
• D. A. Ritchie,
• R. Torre,
• M. S. Vitiello
• & P. De Natale

Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO₃ waveguide and covering the 0.1–6 THz frequency range. We show that even a small fraction (<100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.

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