Abstract-Grating-Graphene Metamaterial as a Platform for Terahertz Nonlinear Photonics

 

Jan-Christoph Deinert, David Alcaraz Iranzo, Raúl Pérez, Xiaoyu Jia, Hassan A. Hafez, Igor Ilyakov, Nilesh Awari, Min Chen, Mohammed Bawatna, Alexey N. Ponomaryov, Semyon Germanskiy, Mischa Bonn, Frank H.L. Koppens, Dmitry Turchinovich, Michael Gensch, Sergey Kovalev,  Klaas-Jan Tielrooij 

https://pubs.acs.org/doi/full/10.1021/acsnano.0c08106

Nonlinear optics is an increasingly important field for scientific and technological applications, owing to its relevance and potential for optical and optoelectronic technologies. Currently, there is an active search for suitable nonlinear material systems with efficient conversion and a small material footprint. Ideally, the material system should allow for chip integration and room-temperature operation. Two-dimensional materials are highly interesting in this regard. Particularly promising is graphene, which has demonstrated an exceptionally large nonlinearity in the terahertz regime. Yet, the light–matter interaction length in two-dimensional materials is inherently minimal, thus limiting the overall nonlinear optical conversion efficiency. Here, we overcome this challenge using a metamaterial platform that combines graphene with a photonic grating structure providing field enhancement. We measure terahertz third-harmonic generation in this metamaterial and obtain an effective third-order nonlinear susceptibility with a magnitude as large as 3 × 10–8 m2/V2, or 21 esu, for a fundamental frequency of 0.7 THz. This nonlinearity is 50 times larger than what we obtain for graphene without grating. Such an enhancement corresponds to a third-harmonic signal with an intensity that is 3 orders of magnitude larger due to the grating. Moreover, we demonstrate a field conversion efficiency for the third harmonic of up to ∼1% using a moderate field strength of ∼30 kV/cm. Finally, we show that harmonics beyond the third are enhanced even more strongly, allowing us to observe signatures of up to the ninth harmonic. Grating-graphene metamaterials thus constitute an outstanding platform for commercially viable, CMOS-compatible, room-temperature, chip-integrated, THz nonlinear conversion applications.

Abstract-Fast and Sensitive Terahertz Detection Using an Antenna-Integrated Graphene pn Junction

Sebastián Castilla, Bernat Terrés, Marta Autore, Leonardo Viti, Jian Li, Alexey Y. Nikitin, Ioannis Vangelidis, Kenji Watanabe, Takashi Taniguchi, Elefterios Lidorikis, Miriam S. Vitiello, Rainer Hillenbrand, Klaas-Jan Tielrooij, Frank H.L. Koppens

https://arxiv.org/abs/1905.01881

Although the detection of light at terahertz (THz) frequencies is important for a large range of applications, current detectors typically have several disadvantages in terms of sensitivity, speed, operating temperature, and spectral range. Here, we use graphene as a photoactive material to overcome all of these limitations in one device. We introduce a novel detector for terahertz radiation that exploits the photothermoelectric (PTE) effect, based on a design that employs a dual-gated, dipolar antenna with a gap of 100 nm. This narrow-gap antenna simultaneously creates a pn junction in a graphene channel located above the antenna and strongly concentrates the incoming radiation at this pn junction, where the photoresponse is created. We demonstrate that this novel detector has an excellent sensitivity, with a noise-equivalent power of 80 pW-per-square-root-Hz at room temperature, a response time below 30 ns (setup-limited), a high dynamic range (linear power dependence over more than 3 orders of magnitude) and broadband operation (measured range 1.8-4.2 THz, antenna-limited), which fulfills a combination that is currently missing in the state-of-the-art detectors. Importantly, on the basis of the agreement we obtained between experiment, analytical model, and numerical simulations, we have reached a solid understanding of how the PTE effect gives rise to a THz-induced photoresponse, which is very valuable for further detector optimization.