Grating-Graphene Metamaterial as a Platform for Terahertz Nonlinear Photonics

Abstract

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.

Hot carriers in graphene – fundamentals and applications

“…The attractiveness of graphene in this field comes from its small footprint and high efficiency, as shown by observation of the record value of 1% conversion efficiency obtained with a grating-graphene metamaterial using a moderate field strength of ∼30 kV cm −1 (ref. 174 ) ( Fig. 21c ).…”

“…In the future, THz nonlinear optics with graphene could offer a rich playground for on-chip signal processing 174 and for the study of the hydrodynamic regime (see 5.1.4) with Dirac fermions. 175 …”

“…The heating-cooling dynamics play a crucial role in observing the THz harmonics created by a multicycle incident THz pulse, as detailed in ref. 56 and 173. In the future, THz nonlinear optics with graphene could offer a rich playground for on-chip signal processing 174 and for the study of the hydrodynamic regime (see 5.1.4) with Dirac fermions. 175…”

Recent Advances in Terahertz Photonic Technologies Based on Graphene and Their Applications

“…[ 96 ] Another recent experimental work based on a hybrid metamaterial made of a metallic grating combined with graphene is shown in Figure a. [ 97 ] In this experiment, a narrow‐band THz waveform was focused on the sample and the electric field of the transmitted waveform was measured as a function of time. The harmonic generation of the proposed metamaterial structure was demonstrated by comparing the field strength of the transmitted signal to that of incident light in frequency domain by computing the Fourier transform of the resulted time domain signals.…”

Tuning of Graphene-Based Optical Devices Operating in the Near-Infrared

“…It should be noted that the use of this property of graphene is not limited only to the NIR range; in this regard, electro-optical graphene terahertz modulators can be noted [30][31][32]. The nonlinear photonics of graphene finds many applications, including spatial and spectral control of laser light, all-optical signal processing, ultrafast switching and probing, and frequency multiplication of the terahertz range [33][34][35][36][37][38]. Graphene is also an affordable means for implementing a saturable absorber (SA) [39][40][41][42][43].…”