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We present an electrically switchable graphene terahertz (THz) modulator with a tunable-by-design optical bandwidth and we exploit it to compensate the cavity dispersion of a quantum cascade laser (QCL). Electrostatic gating is achieved by a metal-grating used as a gate electrode, with an HfO2/AlOx gate dielectric on top. This is patterned on a polyimide layer, which acts as a quarter wave resonance cavity, coupled with an Au reflector underneath. We get 90% modulation depth of the intensity, combined with a 20 kHz electrical bandwidth in the 1.9 _ 2.7 THz range. We then integrate our modulator with a multimode THz QCL. By adjusting the modulator operational bandwidth, we demonstrate that the graphene modulator can partially compensates the QCL cavity dispersion, resulting in an integrated laser behaving as a stable frequency comb over 35% of the laser operational range, with 98 equidistant optical modes and with a spectral coverage of ~ 1.2 THz. This has significant potential for frontier applications in the terahertz, as tunable transformation-optics devices, active photonic components, adaptive and quantum optics, and as a metrological tool for spectroscopy at THz frequencies.
Graphene is a 2D material with appealing electronic and optoelectronic properties. It is a zero-bandgap material with valence and conduction bands meeting in a single point (Dirac point) in the momentum space. Its conductivity can be changed by shift
We report a THz reflectarray metasurface which uses graphene as active element to achieve beam steering, shaping and broadband phase modulation. This is based on the creation of a voltage controlled reconfigurable phase hologram, which can impart dif
Graphene offers a possibility for actively controlling plasmon confinement and propagation by tailoring its spatial conductivity pattern. However, implementation of this concept has been hampered because uncontrollable plasmon reflection is easily in
We report on experimental studies of terahertz (THz) radiation transmission through grating-gate graphene-channel transistor nanostructures and demonstrate room temperature THz radiation amplification stimulated by current-driven plasmon excitations.
In this paper, a broadband tunable polarization converter based on graphene metasurfaces is proposed. This polarization converter works in the terahertz (THz) frequency region, using the advantage of graphene characteristics to have a tunable frequen