The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here, we expand the range of such structures to photoactive ones by using semiconducting transition metal dichalcogenides (TMDCs)/graphene stacks. Van Hove singularities in the electronic density of states of TMDC guarantees enhanced light-matter interactions, leading to enhanced photon absorption and electron-hole creation (which are collected in transparent graphene electrodes). This allows development of extremely efficient flexible photovoltaic devices with photoresponsivity above 0.1 ampere per watt (corresponding to an external quantum efficiency of above 30%).

Two-dimensional graphene plasmon-based technologies will enable the development of fast, compact and inexpensive active photonic elements because, unlike plasmons in other materials, graphene plasmons can be tuned via the doping level. Such tuning is harnessed within terahertz quantum cascade lasers to reversibly alter their emission. This is achieved in two key steps: First by exciting graphene plasmons within an aperiodic lattice laser and, second, by engineering photon lifetimes, linking graphene's Fermi energy with the round-trip gain. Modal gain and hence laser spectra are highly sensitive to the doping of an integrated, electrically controllable, graphene layer. Demonstration of the integrated graphene plasmon laser principle lays the foundation for a new generation of active, programmable plasmonic metamaterials with major implications across photonics, material sciences and nanotechnology.Among the many intriguing properties of graphene, its plasmonic characteristics are some of the most fascinating and potentially useful [1,2]. Long-lived, tunable intrinsic graphene surface plasmons (SP) have already been demonstrated in a number of experiments [3][4][5][6][7][8][9], including optical modulators [10,11], providing the potential for applications [12,13]. In contrast to the noble metals that are usually used in SP devices [13,14], graphene's Fermi energy, E F , and carrier concentration, n s (and therefore its conductivity and SP mode properties), can be altered, for example by electrical gating and surface doping [3,15,16]. Consequently, the behavior of graphene SP-based structures can be modified in situ, without the need for structural device changes. In particular, graphene's optical and plasmonic properties are tunable in the terahertz (THz) spectral region [3,17], giving rise to the possibility of compact electrically controllable THz optical components [18]. We incorporated graphene into a plasmonic THz laser microcavity to dynamically modulate round-trip modal gain values and therefore laser emission via E F . In this way gated graphene becomes a powerful tool with which to control the fundamental properties of a laser -a tool that is potentially extremely fast and all electrical in nature, with negligible electrical power requirements.The interaction between light and matter can be altered by manipulating the electromagnetic density-of-states (DOS) using a micro resonator [19,20]. By incorporating a photonic lattice or plasmonic structure into a laser, one can control the frequency and amplification of resonant modes and hence manipulate the properties of lasing emission [21][22][23]. Furthermore, by breaking the regularity of these structures it is possible to modulate the photon DOS and hence light-matter interaction at several frequencies simultaneously. This technique was used recently to develop an aperiodic distributed feedback (ADFB) cavity laser with a lattice which is in essence a computergenerated hologram [24,25]. The hologram digitally encodes the Fourier transform of a desired optica...

Abstract:The superlatives of graphene cover a whole range of properties: electrical, chemical, mechanical, thermal and others. These special properties earn graphene a place in current or future applications. Here we demonstrate one such application -adaptive contact lenses based on liquid crystals, where simultaneously the high electrical conductivity, transparency, flexibility and elasticity of graphene are being utilised. In our devices graphene is used as a transparent conductive coating on curved PMMA substrates. The adaptive lenses provide a +0.7 D change in optical power with an applied voltage of 7.1 V rms -perfect to correct presbyopia, the age-related condition that limits the near focus ability of the eye. Frye, R. Pashaie, S. Thongpang, Z. Ma, and J. C. Williams, "Graphene-based carbon-layered electrode array technology for neural imaging and optogenetic applications," Nature Commun. 5, 5258 (2014).

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