Active Terahertz Modulator and Slow Light Metamaterial Devices with Hybrid Graphene-Superconductor Photonic Integrated Circuits.

Metamaterial photonic integrated circuits with arrays of hybrid graphene-superconductor coupled split-ring resonators (SRR) capable of modulating and slowing down terahertz (THz) light are introduced and proposed. The hybrid device's optical responses, such as electromagnetic-induced transparency (EIT) and group delay, can be modulated in several ways. First, it is modulated electrically by changing the conductivity and carrier concentrations in graphene. Alternatively, the optical response can be modified by acting on the device temperature sensitivity by switching Nb from a lossy normal phase to a low-loss quantum mechanical phase below the transition temperature (Tc) of Nb. Maximum modulation depths of 57.3% and 97.61% are achieved for EIT and group delay at the THz transmission window, respectively. A comparison is carried out between the Nb-graphene-Nb coupled SRR-based devices with those of Au-graphene-Au SRRs, and significant enhancements of the THz transmission, group delay, and EIT responses are observed when Nb is in the quantum mechanical phase. Such hybrid devices with their reasonably large and tunable slow light bandwidth pave the way for the realization of active optoelectronic modulators, filters, phase shifters, and slow light devices for applications in chip-scale future communication and computation systems

Metamaterial/graphene active terahertz modulators

Within the last years there has been a tremendous thrust into research and technology in the THz spectral region (broadly defined as 0.1-10 THz) mainly driven by the unique potential where this radiation finds applications in, such as imaging, spectroscopy and communication. In all these fields a fast, integrated and versatile platform for modulating light is required. Metamaterial/graphene devices fulfill all these requirements as their subwavelength nature lends itself naturally to strong light-matter interaction, and therefore highly efficient and miniaturized devices. Graphene's unique properties, e.g. the large carrier concentration modulation, provide a large degree of compatibility with several architectures which can be exploited in a range of modulation or detection schemes. Finally, metamaterial/graphene devices realize a fast, versatile platform, which can be easily scaled to other frequencies, and adapted into amplitude, frequency, polarization and phase modulators, as well as integrated detectors, for the next generation of wireless-communication

Terahertz polarisation modulator by electronic control of graphene loaded chiral metamaterial device

Terahertz (THz) science and technology has experienced tremendous progress in recent years, such as in spectroscopy, imaging, pharmaceutical research [1] and wireless communications. These applications require electrically tuneable devices to modulate the THz properties, including the amplitude, frequency and polarization. The integration of resonant plasmonic/metamaterial devices with graphene, has proved a successful route for the realisation of fast reconfigurable, efficient THz optoelectronic devices [2], via electrical tuning of graphene integrated with plasmonic resonant structures. An active THz modulator is presented based on a chiral metamaterial array containing metallic features, loaded with graphene. The device makes use of an electromagnetically induced transparency analogue produced via the capacitive coupling of bright and dark resonators, the latter actively damped with graphene, exploited for frequency modulation in Ref. [2]. The active area is 1.2 x 1.2 mm, consisting of a 2D chiral metamaterial array comprising 27 x 27 unit cells, shown in Fig. 1a. The resonators were defined using electron-beam lithography, and thermal evaporation of Ti/Au (10/70nm). These features were deposited on top of a 300 nm insulating layer of SiO2 on a boron p-doped silicon substrate. Chemical vapour deposition grown graphene was defined into 3.25 x 3.25 µm2 patches through e-beam lithography

Bow-tie plasmonic arrays loaded with graphene for the fast room temperature detection of terahertz quantum cascade lasers

We present a fast room temperature terahertz detector based on interdigitated bow-tie antennas asymmetrically doping and contacting graphene. The device was tested with a 2 THz quantum cascade laser yielding a responsivity of 0.5 μA/W

Fast terahertz optoelectronic amplitude modulator based on plasmonic metamaterial antenna arrays and graphene

The growing interest in terahertz (THz) technologies in recent years has seen a wide range of demonstrated applications, spanning from security screening, non-destructive testing, gas sensing, to biomedical imaging and communication. Communication with THz radiation offers the advantage of much higher bandwidths than currently available, in an unallocated spectrum. For this to be realized, optoelectronic components capable of manipulating THz radiation at high speeds and high signal-to-noise ratios must be developed. In this work we demonstrate a room temperature frequency dependent optoelectronic amplitude modulator working at around 2 THz, which incorporates graphene as the tuning medium. The architecture of the modulator is an array of plasmonic dipole antennas surrounded by graphene. By electrostatically doping the graphene via a back gate electrode, the reflection characteristics of the modulator are modified. The modulator is electrically characterized to determine the graphene conductivity and optically characterization, by THz time-domain spectroscopy and a single-mode 2 THz quantum cascade laser, to determine the optical modulation depth and cut-off frequency. A maximum optical modulation depth of ~ 30% is estimated and is found to be most (least) sensitive when the electrical modulation is centered at the point of maximum (minimum) differential resistivity of the graphene. A 3 dB cut-off frequency > 5 MHz, limited only by the area of graphene on the device, is reported. The results agree well with theoretical calculations and numerical simulations, and demonstrate the first steps towards ultra-fast, graphene based THz optoelectronic devices. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Research data supporting "Fast modulation of terahertz quantum cascade lasers using graphene loaded plasmonic antennas"

This research data supports “Fast modulation of terahertz quantum cascade lasers using graphene loaded plasmonic antennas” which has been published in “ACS Photonics”.The first two .opj files represent the data of the modulation depth for the arrays corresponding to a characteristic length of 24 and 26 um, respectively. Mod_speed.opj contains the data of the modulation speed acquired for the 26 um array. Simulation_tds reports the simulations performed with the finite element software Comsol multiphysics and elaborated with the software origin. tds.opj reports the time-domain spectroscopy measurements elaborated with Matlab and here reported in Origin. Source-drain_resistance.opj reports the electrical characterization for the arrays with 24 and 26 um characterisitics lengths.This work was supported by the EPSRC [grant numbers EP/J017671/1, Coherent Terahertz Systems Grant No. EP/L019922/1 and EP/K016636/1, GRAPHTED]