Thermal Radiation From Carbon Nanotube in Terahertz Range

The thermal radiation from an isolated finite-length carbon nanotube (CNT) is theoretically investigated both in near- and far-field zones. The formation of the discrete spectrum in metallic CNTs in the terahertz range is demonstrated due to the reflection of strongly slowed-down surface-plasmon modes from CNT ends. The effect does not appear in semiconductor CNTs. The concept of CNT as a thermal nanoantenna is proposed.Comment: 5 pages, 3 figure

Sinusoidally-Modulated Graphene Leaky-Wave Antenna for Electronic Beamscanning at THz

This paper proposes the concept, analysis and design of a sinusoidally-modulated graphene leaky-wave antenna with beam scanning capabilities at a fixed frequency. The antenna operates at terahertz frequencies and is composed of a graphene sheet transferred onto a back-metallized substrate and a set of polysilicon DC gating pads located beneath it. In order to create a leaky-mode, the graphene surface reactance is sinusoidally-modulated via graphene's field effect by applying adequate DC bias voltages to the different gating pads. The pointing angle and leakage rate can be dynamically controlled by adjusting the applied voltages, providing versatile beamscanning capabilities. The proposed concept and achieved performance, computed using realistic material parameters, are extremely promising for beamscanning at THz frequencies, and could pave the way to graphene-based reconfigurable transceivers and sensors.Comment: 7 pages; 10 figure

Ultra-compact modulators based on novel CMOS-compatible plasmonic materials

We propose several planar layouts of ultra-compact plasmonic waveguide modulators that utilize alternative CMOS-compatible materials. The modulation is efficiently achieved by tuning the carrier concentration in a transparent conducting oxide layer, thereby tuning the waveguide either in plasmonic resonance or off-resonance. Resonance significantly increases the absorption coefficient of the plasmonic waveguide, which enables larger modulation depth. We show that an extinction ratio of 86 dB/um can be achieved, allowing for a 3-dB modulation depth in less than one micron at the telecommunication wavelength. Our multilayer structures can potentially be integrated with existing plasmonic and photonic waveguides as well as novel semiconductor-based hybrid photonic/electronic circuits

Nanoscale Architectures for Smart Bio-Interfaces: Advances and Challenges

Volcanology & seismolog

Ultra-long-range symmetric plasmonic waveguide for high-density and compact photonic devices

This study reports a symmetric hybrid plasmonic waveguide consisting of a cylindrical metal nanowire surrounded by low-index SiO2 and high-index Si covered with SiO2. The symmetric circumambience relative to the metal nanowire significantly facilitates the present design to minimize the energy attenuation resulting from Ohmic losses while retaining highly confined modes guided in the low-index nanoscale gaps between the metal nanowire and the high-index Si. The geometric dependence of the mode characteristics on the proposed structure is analyzed in detail, showing long propagation lengths beyond 10 mm with normalized mode areas on the order of 10−2. In addition to enabling the building of long-range plasmonic circuit interconnects, the compactness and high-density integration of the proposed structure are examined by analyzing crosstalk in a directional coupler composed of two such waveguides and bending losses for a 90° bend. A relatively short coupling length of 1.16 μm is obtained at a center-to-center separation of 0.26 μm between adjacent waveguides. Increasing the separation to 1.65 μm could completely prevent coupling between waveguides. Power transmission exceeds 80% in the case of a 90° bend with small radius of curvature of 0.5 μm. Moreover, the dependence of spectral response on coupling length and the transmission of a 90° bend, ranging from telecom wavelengths of 1.40 to 1.65 μm, are investigated. Over a wide wavelength range, a strong coupling length dependence on wavelength and a high transmission for a 90° bend also make the proposed plasmonic waveguide promising for the realization of wavelength-selective components

Metasurfaces Based on Phase-Change Material as a Reconfigurable Platform for Multifunctional Devices

Integration of phase-change materials (PCMs) into electrical/optical circuits has initiated extensive innovation for applications of metamaterials (MMs) including rewritable optical data storage, metasurfaces, and optoelectronic devices. PCMs have been studied deeply due to their reversible phase transition, high endurance, switching speed, and data retention. Germanium-antimony-tellurium (GST) is a PCM that has amorphous and crystalline phases with distinct properties, is bistable and nonvolatile, and undergoes a reliable and reproducible phase transition in response to an optical or electrical stimulus; GST may therefore have applications in tunable photonic devices and optoelectronic circuits. In this progress article, we outline recent studies of GST and discuss its advantages and possible applications in reconfigurable metadevices. We also discuss outlooks for integration of GST in active nanophotonic metadevices.1115sciescopu

ULTRAFAST OPTICAL RESPONSE AND TRANSPORT PROPERTIES OF STRONTIUM TITANATE-BASED COMPLEX OXIDE NANOSTRUCTURES

As the silicon-based semiconductor integrated circuits led by Moore's Law approaching their physical limits, the search for a new generation of nanoelectronic and nanophotonic devices is becoming a hot topic in this post-Moore era. The strontium titanate-based complex oxide heterostructure appears to be a promising alternative due to its diverse emergent properties. Being able to control the metal-insulator transition at the polar/nonpolar LaAlO3/SrTiO3 interface using conductive atomic force microscopy (c-AFM) lithography has made LaAlO3/SrTiO3, in particular, an attractive platform. Expanding the class of heterostructures which can be controlled at nanoscale dimensions is important for alternative oxide-based nanodevices. In this dissertation, the writing and erasing of nanostructures at the nonpolar/nonpolar oxide interface of CaZrO3/SrTiO3 using c-AFM lithography is investigated. Conducting nanostructures as narrow as 1.2 nm at room temperature is achieved. Low-temperature transport measurements based on these nanostructures provide insight into the electronic structure of the CaZrO3/SrTiO3 interface. Such extreme nanoscale control, with dimensions comparable to most single-walled carbon nanotubes, holds great promise for oxide-based nanoelectronic devices. Nanophotonic devices operating at terahertz frequencies, on the other hand, offer unique information for many applications. In this dissertation, broadband nanoscale terahertz generators based on c-AFM lithography defined LaAlO3/SrTiO3 nanojunctions are proved to be able to detect the plasmonic response of a single gold nanorod. By femtosecond pulse shaping using a home-built pulse shaper, over 100 THz bandwidth selective difference frequency generation at LaAlO3/SrTiO3 nanojunctions is also demonstrated, which has great potential in both studying fundamental light-matter interaction and realizing selective control of rotational or vibrational resonances in nanoparticles. With this unprecedented control of THz field, the two-dimensional (2D) material graphene and its coupling with the quasi-2D LaAlO3/SrTiO3 interface are also under investigation. The preliminary data shows evidence for graphene response up to 60 THz. These results help to fill the terahertz gap as well as offer new opportunities for oxide-based nanophotonic devices or even hybrid optoelectronic integrated circuits