We report on the ultrafast modulation of a graphene loaded artificial metasurface realized on a SiO2/Si substrate by near-IR laser pump, detected via terahertz probe at the resonant frequency of ∼0.8 THz. The results have been acquired by setting the Fermi energy of graphene at the Dirac point via electrostatic gating and illuminating the sample with 40 fs pump pulses at different fluences, ranging from 0.9 to 0.018 mJ/cm2. The sub-ps conductivity rising time was attributed to the combined effect of the ultrafast generation of hot carriers in graphene and electron–hole generation in silicon. In correspondence of the resonance, it was possible to clearly distinguish a partial recovery time of ∼2 ps mainly due to carrier-phonon relaxation in graphene, superimposed to the > 1 ns recovery time of silicon. The resonant metasurface yielded ∼6 dB modulation depth in E-field amplitude at 0.8 THz for the range of fluences considered. These measurements set an upper limit for the reconfiguration speed achievable by graphene-based terahertz devices. At the same time, this work represents a great progress toward the realization of an ultrafast THz optoelectronic platform for a plethora of applications, ranging from the investigation of the ultrastrong light-matter regime to the next generation wireless communications.

All-electronicultrafast control of terahertz radiation is demonstrated in integrated metamaterial/graphene devices. By electrostatic gating the graphene conductivity, the overall optical response of the incident terahertz E-field is modified. Depending on the configuration, amplitude, phase, and polarization of terahertz radiation could be modulated with GHz range of reconfiguration speed. An extinction ratio of >7.6 dB in amplitude is achieved at the resonant frequency of 0.75 THz. Additionally, a relative phase shift of >17.4 • is observed around a frequency of 0.68 THz. When operating as a polarization modulator, the device has reported an ellipticity change of ∼ 40% at a frequency of 0.68 THz and a dynamic rotation of the polarization plane by >9 • at resonance. The switching capability of the modulators has been investigated all electronically reporting a speed exceeding 3 GHz, only limited by the available instrumentation. Consequently, GHzspeed of modulation can be achieved for frequencies around 0.75 THz. These results represent a breakthrough for all applications where a fast, versatile, and efficient modulation of THz radiation is required, such as in next-generation wireless communication, quantum electronics, and ultrafast imaging.

Metamaterial resonators have become an efficient and versatile platform in the terahertz frequency range, finding applications in integrated optical devices, such as active modulators and detectors, and in fundamental research, e.g., ultrastrong light−matter investigations. Despite their growing use, characterization of modes supported by these subwavelength elements has proven to be challenging and it still relies on indirect observation of the collective far-field transmission/reflection properties of resonator arrays. Here, we present a broadband time-domain spectroscopic investigation of individual metamaterial resonators via a THz aperture scanning near-field microscope (a-SNOM). The time-domain a-SNOM allows the mapping and quantitative analysis of strongly confined modes supported by the resonators. In particular, a cross-polarized configuration presented here allows an investigation of weakly radiative modes. These results hold great potential to advance future metamaterial-based optoelectronic platforms for fundamental research in THz photonics.