Abstract-Broadband gate-tunable terahertz plasmons in graphene heterostructures

Baicheng Yao, Yuan Liu, Shu-Wei Huang, Chanyeol Choi, Zhenda Xie, Jaime Flor Flores, Yu Wu, Mingbin Yu, Dim-Lee Kwong, Yu Huang, Yunjiang Rao, Xiangfeng Duan,  Chee Wei Wong,

https://www.nature.com/articles/s41566-017-0054-7

Graphene, a unique two-dimensional material comprising carbon in a honeycomb lattice1, has brought breakthroughs across electronics, mechanics and thermal transport, driven by the quasiparticle Dirac fermions obeying a linear dispersion2,3. Here, we demonstrate a counter-pumped all-optical difference frequency process to coherently generate and control terahertz plasmons in atomic-layer graphene with octave-level tunability and high efficiency. We leverage the inherent surface asymmetry of graphene for strong second-order nonlinear polarizability4,5, which, together with tight plasmon field confinement, enables a robust difference frequency signal at terahertz frequencies. The counter-pumped resonant process on graphene uniquely achieves both energy and momentum conservation. Consequently, we demonstrate a dual-layer graphene heterostructure with terahertz charge- and gate-tunability over an octave, from 4.7 THz to 9.4 THz, bounded only by the pump amplifier optical bandwidth. Theoretical modelling supports our single-volt-level gate tuning and optical-bandwidth-bounded 4.7 THz phase-matching measurements through the random phase approximation, with phonon coupling, saturable absorption and below the Landau damping, to predict and understand graphene plasmon physics.

Abstract-Globally stable microresonator Turing pattern formation for coherent high-power THz radiation on-chip

Shu-Wei Huang, Jinghui Yang, Shang-Hua Yang, Mingbin Yu, Dim-Lee Kwong, T. Zelevinsky, Mona Jarrahi, and Chee Wei Wong

https://journals.aps.org/prx/accepted/44076K0cIb517709416d6635e46a4d487511ca7c6

In nonlinear microresonators driven by continuous-wave (cw) lasers, Turing patterns have been studied in the formalism of Lugiato-Lefever equation with emphasis on its high coherence and exceptional robustness against perturbations. Destabilization of Turing pattern and transition to spatio-temporal chaos, however, limits the available energy carried in the Turing rolls and prevents further harvest of their high coherence and robustness to noise. Here we report a novel scheme to circumvent such destabilization, by incorporating the effect of local mode hybridizations, and attain globally stable Turing pattern formation in chip-scale nonlinear oscillators with significantly enlarged parameter space, achieving a record high power conversion efficiency of 45{\%} and an elevated peak-to-valley contrast of 100. The stationary Turing pattern is discretely tunable across 430 GHz on a THz carrier, with a fractional frequency sideband non-uniformity measured at 7.3\texttimes 10}\mathbf{-14}{. We demonstrate the simultaneous microwave and optical coherence of the Turing rolls at different evolution stages through ultrafast optical correlation techniques. The free-running Turing roll coherence, 9 kHz in 200 ms and 160 kHz in 20 minutes, is transferred onto a plasmonic photomixer for one of the highest power THz coherent generation at room-temperature, with 1.1{\%} optical-to-THz power conversion. Its long-term stability can be further improved by more than two orders of magnitude, reaching an Allan deviation of 6\texttimes 10}\mathbf{-10}{ at 100 s, with a simple computer-aided ...