Ultrafast modulation of a THz metamaterial/graphene array integrated device

Abstract

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.