Abstract-Terahertz Frequency Combs Exploiting an On-Chip, Solution-Processed, Graphene-Quantum Cascade Laser Coupled-Cavity

 

Francesco P. Mezzapesa,  Katia Garrasi, Johannes Schmidt, Luca Salemi, Valentino Pistore, Lianhe Li, A. Giles Davies, Edmund H. Linfield, Michael Riesch, Christian Jirauschek, Tian Carey, Felice Torrisi, Andrea C. Ferrari,  Miriam S. Vitiello

https://pubs.acs.org/doi/10.1021/acsphotonics.0c01523#

The ability to engineer quantum-cascade-lasers (QCLs) with ultrabroad gain spectra, and with a full compensation of the group velocity dispersion, at terahertz (THz) frequencies, is key for devising monolithic and miniaturized optical frequency-comb-synthesizers (FCSs) in the far-infrared. In THz QCLs four-wave mixing, driven by intrinsic third-order susceptibility of the intersubband gain medium, self-locks the optical modes in phase, allowing stable comb operation, albeit over a restricted dynamic range (∼20% of the laser operational range). Here, we engineer miniaturized THz FCSs, comprising a heterogeneous THz QCL, integrated with a tightly coupled, on-chip, solution-processed, graphene saturable-absorber reflector that preserves phase-coherence between lasing modes, even when four-wave mixing no longer provides dispersion compensation. This enables a high-power (8 mW) FCS with over 90 optical modes, through 55% of the laser operational range. We also achieve stable injection-locking, paving the way to a number of key applications, including high-precision tunable broadband-spectroscopy and quantum-metrology.

Abstract-HBN-encapsulated, graphene-based room-temperature terahertz receivers with high speed and low noise

Leonardo Viti, David G. Purdie, Antonio Lombardo, Andrea C. Ferrari, Miriam S. Vitiello

https://arxiv.org/abs/2004.10011

Uncooled Terahertz (THz) photodetectors (PDs) showing fast (ps) response and high sensitivity (noise equivalent power (NEP) < nWHz−1/2) over a broad (0.5THz-10THz) frequency range are needed for applications in high-resolution spectroscopy (relative accuracy ~ 
10−11), metrology, quantum information, security, imaging, optical communications. However, present THz receivers cannot provide the required balance between sensitivity, speed, operation temperature and frequency range. Here, we demonstrate an uncooled THz PD combining the low (~2000 kBμm−2) electronic specific heat of high mobility (> 50000 cm2V−1s−1) hBN-encapsulated graphene with the asymmetric field-enhancement produced by a bow-tie antenna resonating at 3 THz. This produces a strong photo-thermoelectric conversion, which simultaneously leads to a combination of high sensitivity (NEP ≤ 160 pWHz−1/2), fast response time (≤3.3ns) and a four orders of magnitude dynamic range, making our devices the fastest, broadband, low noise, room temperature THz PD to date.

Abstract-Graphene Reflectarray Metasurface for Terahertz Beam Steering and Phase Modulation

Michele Tamagnone, Santiago Capdevila, Antonio Lombardo, Jingbo Wu, Amaia Zurutuza, Alba Centeno, Adrian M. Ionescu, Andrea C. Ferrari, Juan R. Mosig

https://arxiv.org/abs/1806.02202

We report a THz reflectarray metasurface which uses graphene as active element to achieve beam steering, shaping and broadband phase modulation. This is based on the creation of a voltage controlled reconfigurable phase hologram, which can impart different reflection angles and phases to an incident beam, replacing bulky and fragile rotating mirrors used for terahertz imaging. This can also find applications in other regions of the electromagnetic spectrum, paving the way to versatile optical devices including light radars, adaptive optics, electro-optical modulators and screens.

Abstract-High performance bilayer-graphene Terahertz detectors

Davide Spirito, Dominique Coquillat, Sergio L. De Bonis, Antonio Lombardo, Matteo Bruna, Andrea C. Ferrari, Vittorio Pellegrini, Alessandro Tredicucci, Wojciech Knap, Miriam S. Vitiello

http://arxiv.org/abs/1312.3737
We report bilayer-graphene field effect transistors operating as THz broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity ∼1.2V/W(1.3mA/W) and a noise equivalent power ∼2×10−9W/Hz−1/2 in the 0.29-0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.