Strong THz and Infrared Optical Forces on a Suspended Single-Layer Graphene Sheet

Single-layer graphene exhibits exceptional mechanical properties attractive for optomechanics: it combines low mass density, large tensile modulus, and low bending stiffness. However, at visible wavelengths, graphene absorbs weakly and reflects even less, thereby is inadequate to generate large optical forces needed in optomechanics. Here, we numerically show that a single-layer graphene sheet is sufficient to produce strong optical forces under terahertz or infrared illumination. For a system as simple as graphene suspended atop a uniform substrate, high reflectivity from the substrate is crucial in creating a standing-wave pattern, leading to a strong optical force on graphene. This force is readily tunable in amplitude and direction by adjusting the suspension height. In particular, repellent optical forces can levitate graphene to a series of stable equilibrium heights above the substrate. One of the key parameters to maximize the optical force is the excitation frequency: peak forces are found near the scattering frequency of free carriers in graphene. With a dynamically controllable Fermi level, graphene opens up new possibilities of tunable nanoscale optomechanical devices

Large Cavity-Optomechanical Coupling with Graphene at Infrared and Terahertz Frequencies

Graphene exhibits many unusual elastic properties, making it an intriguing material for mechanical measurement and actuation at the quantum limit. We theoretically examine the viability of graphene for cavity optomechanics from near-infrared to terahertz wavelengths, fully taking into account its large optical absorption and dispersion. A large optomechanical coupling coefficient, on the same order of that observed in state-of-the-art optomechanical materials, can be realized in the mid-infrared spectrum with highly doped graphene, a high optical quality factor, and optimal positioning of graphene. Around 100 THz, the dispersive coupling coefficient reaches 180 MHz/nm and 500 MHz/nm in the resolved and unresolved sideband regimes, respectively. We find that predominantly dispersive coupling requires a high graphene Fermi level and mid-infrared excitation, while predominantly dissipative coupling favors a moderate graphene Fermi level and near-infrared excitation

Electrical Switching of Infrared Light Using Graphene Integration with Plasmonic Fano Resonant Metasurfaces

Graphene has emerged as a promising optoelectronic material because its optical properties can be rapidly and dramatically changed using electric gating. Graphene’s weak optical response, especially in the infrared part of the spectrum, remains the key challenge to developing practical graphene-based optical devices such as modulators, infrared detectors, and tunable reflect-arrays. Here it is experimentally and theoretically demonstrated that a plasmonic metasurface with two Fano resonances can dramatically enhance the interaction of infrared light with single layer graphene. Graphene’s plasmonic response in the Pauli blocking regime is shown to cause strong spectral shifts of the Fano resonances without inducing additional nonradiative losses. It is shown that such electrically controllable spectral shift, combined with the narrow spectral width of the metasurface’s Fano resonances, enables reflectivity modulation by nearly an order of magnitude. We also demonstrate that metasurface-based enhancement of the interaction between graphene and infrared light can be utilized to extract one of the key optical parameters of graphene: the free carrier scattering rate. Numerical simulations demonstrate the possibility of strong active modulation of the phase of the reflected light while keeping the reflectivity nearly constant, thereby paving the way to tunable infrared lenses and beam steering devices based on electrically controlled graphene integrated with resonant metasurfaces

Improved Electrical Conductivity of Graphene Films Integrated with Metal Nanowires

Polycrystalline graphene grown by chemical vapor deposition (CVD) on metals and transferred onto arbitrary substrates has line defects and disruptions such as wrinkles, ripples, and folding that adversely affect graphene transport properties through the scattering of the charge carriers. It is found that graphene assembled with metal nanowires (NWs) dramatically decreases the resistance of graphene films. Graphene/NW films with a sheet resistance comparable to that of the intrinsic resistance of graphene have been obtained and tested as a transparent electrode replacing indium tin oxide films in electrochromic (EC) devices. The successful integration of such graphene/NW films into EC devices demonstrates their potential for a wide range of optoelectronic device applications

Contrast between Surface Plasmon Polariton-Mediated Extraordinary Optical Transmission Behavior in Epitaxial and Polycrystalline Ag Films in the Mid- and Far-Infrared Regimes

In this Letter we report a comparative study, in the infrared regime, of surface plasmon polariton (SPP) propagation in epitaxially grown Ag films and in polycrystalline Ag films, all grown on Si substrates. Plasmonic resonance features are analyzed using extraordinary optical transmission (EOT) measurements, and SPP band structures for the two dielectric/metal interfaces are investigated for both types of film. At the Si/Ag interface, EOT spectra show almost identical features for epitaxial and polycrystalline Ag films and are characterized by sharp Fano resonances. On the contrary, at the air/Ag interface, dramatic differences are observed: while the epitaxial film continues to exhibit sharp Fano resonances, the polycrystalline film shows only broad spectral features and much lower transmission intensities. In corroboration with theoretical simulations, we find that surface roughness plays a critical role in SPP propagation for this wavelength range