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In recent years, a great deal of effort has been made to create terahertz (THz) devices with metamaterials (MM). Among these devices, perfect absorbers and modulators are highly desired in THz system such as communication, remote sensing, imaging, and astronomy. MM absorbers have a variety of potential applications including thermal emitters, detector, stealth technology, phase imaging. High-speed modulators, which allow actively control the spatial transmission (reflection) of an incident THz wave, is the key components of an advanced communication system. In this presentation, we firstly introduce the basic structure and work principle of MM devices, and then we report our recent progress in the design, fabrication and and measurement of the quite a few new MM devices. And as a close to this presentation, we demonstrate the application of our devices in Terahertz communication system.

[Proceeding of]: META'16: The 7th International Conference on Metamaterials, Photonic Crystals and Plasmonics: July 25-28, 2016, Málaga, Spain. In this work, we propose and design a dielectric metasurface based on Silicon (Si)subwavelength pillars. A previous study of the directional conditions of the scattering is carried out inorder to obtain the optimum sizes. The metasurface can operate as a band-stop filter to realize blocking back THz waves in the designed band range, while transparent transmission over the rest of the range. This work has been supported by Ministerio de Economía y Competitividad of Spain (grant no. TEC2013-50138-EXP & TEC2013-47342-C2-2-R) and the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid. Publicado

Metasurface, as a kind of metamaterials with only one or two layers of functional structures, has arouses a world-wide research enthusiasm during the past several years. Especially, recent studies on metasurfaces working in the terahertz regime has partly fullfilled the emergent lack for the terahertz devices, which is a long-term bottleneck on the terahertz science and technology. Until now, most terahertz metasurfaces were designed, demonstrated and applied for the far-field utilization. However, in recent years, kinds of near-field terahertz technique have become more and more powerful and convenient to use, which facilities a new aspect of terahertz metasurface research. Here we presented the recent terahertz near-field studies on several metasurface-based terahertz devices, including two anomalous surface wave couplers and a meta-lens array. The near-field method not only gives a new tool for the terahertz metasurface study, but also makes the terahertz surface wave researches possible, which may broadly promote the development of the terahertz device technology.

Quantum tunnelling becomes inevitable as gap dimensions in metal structures approach the atomic length scale, and light passing through these gaps can be used to examine the quantum processes at optical frequencies. Here, we report on the measurement of the tunnelling current through a 3-Å-wide metal-graphene-metal gap using terahertz time-domain spectroscopy. By analysing the waveforms of the incident and transmitted terahertz pulses, we obtain the tunnelling resistivity and the time evolution of the induced current and electric fields in the gap and show that the ratio of the applied voltage to the tunnelling current is constant, i.e., the gap shows ohmic behaviour for the strength of the incident electric field up to 30 kV/cm. We further show that our method can be extended and applied to different types of nanogap tunnel junctions using suitable equivalent RLC circuits for the corresponding structures by taking an array of ring-shaped nanoslots as an example.

In this paper the possibility of using a terahertz (THz) electromagnetic waves for detection of coatings' defects was investigated. In the last years, terahertz spectroscopy has gained more interest because of its unique capabilities. THz radiation lies above the frequency range of traditional radio and microwaves but below the range of infrared waves. The THz radiation allows achieving a very good spatial resolution and penetration depth. Moreover, THz inspection has the potential for a higher resolution than ultrasound due to its shorter wavelength. A set of experiments was carried out and the achieved results prove usability of the proposed method.

We present a high-performance pulsed terahertz emitter based on a two-dimensional array of plasmonic nano-antennas, offering significantly higher radiation power levels compared to the state-of-the art. This significant performance enhancement is due to unique capabilities of nano-antenna arrays, inducing significantly stronger radiating dipole moments at terahertz frequencies. The presented terahertz emitter is fabricated on an ErAs:InGaAs substrate to operate at telecommunication optical wavelengths at which compact and high-performance optical sources are commercially available. We experimentally demonstrate record-high terahertz radiation power levels as high as 300 μW over 0.1–5 THz frequency range.

We present a high-performance terahertz emitter based on plasmonic photomixing antennas. By use of plasmonic antennas, a large portion of photocarriers can reach terahertz radiating elements within a fraction of a terahertz oscillation cycle, resulting in significantly higher optical-to-terahertz conversion efficiencies and terahertz radiation power levels compared to conventional photomixers. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a radiation power of 17 μW at 1 THz, exhibiting a 3-fold higher radiation power level compared to the state-of-the art broadly tunable continuous-wave terahertz emitters.

We study and compare terahertz wave propagation in trapezoidal hollow-core aluminum waveguides with and without ridge with respect to attenuation and single-mode spectral bandwidth. Furthermore, we demonstrate a waveguide-based terahertz interferometer for terahertz sensing based on pure amplitude measurements without the necessity for a direct phase measurement.

Terahertz technology has found numerous applications for the detection of biological and chemical hazardous agents, medical diagnostics, detection of explosives, providing security in buildings, airports, and other public spaces, shortrange covert communications (in the THz and sub-THz windows), and applications in radio astronomy and space research. The expansion of these applications will depend on the development of efficient electronic terahertz sources and sensitive low-noise terahertz detectors. Schottky diode frequency multipliers have emerged as a viable THz source technology reaching a few THz. High speed three terminal electronic devices (FETs and HBTs) have entered the THz range (with cutoff frequencies and maximum frequencies of operation above 1 THz). A new approach called plasma wave electronics recently demonstrated an efficient terahertz detection in GaAs-based and GaN-based HEMTs and in Si MOS, SOI, FINFETs and in FET arrays. This progress in THz electronic technology has promise for a significant expansion of THz applications.

Terahertz imaging has many important potential applications. Due to the failure of Si readout integrated circuits (ROICs) and the thermal mismatch between the photo-detector arrays and the ROICs at temperatures below 40 K, there are big technical challenges to construct terahertz photo-type focal plane arrays. In this work, we report pixel-less photo-type terahertz imagers based on the frequency up-conversion technique. The devices are composed of terahertz quantum-well photo-detectors (QWPs) and near-infrared (NIR) light emitting diodes (LEDs) which are grown in sequence on the same substrates using molecular beam epitaxy. In such an integrated QWP-LED device, photocurrent in the QWP drives the LED to emit NIR light. By optimizing the structural parameters of the QWP-LED, the QWP part and the LED part both work well. The maximum values of the internal and external energy up-conversion efficiencies are around 20% and 0.5%. A laser spot of a homemade terahertz quantum cascade laser is imaged by the QWP-LED together with a commercial Si camera. The pixel-less imaging results show that the image blurring induced by the transverse spreading of photocurrent is negligible. The demonstrated pixel-less imaging opens a new way to realize high performance terahertz imaging devices.

We report on a characterization method of the emission spectrum of mm-Wave and terahertz sources without the use of additional terahertz instruments. It exploits the reciprocal properties of these radiating sources. This method can be applied to any source equipped with an antenna. It has been used to characterize the spectral response of two distinct sources. The first is a 0.35 THz ring oscillator and the second is a 0.55 THz Colpitts oscillator, both implemented in a 65 nm CMOS technology. The results of the proposed characterization method have been verified with an FTIR spectrometer and a commercial harmonic mixer.

We present a high-power, broadband terahertz emitter that operates at telecommunication optical pump wavelengths at which high-performance and compact fiber lasers are commercially available. The presented terahertz emitter is a novel large area photoconductive emitter fabricated on a high resistivity ErAs:InGaAs substrate that utilizes a two-dimensional array of plasmonic nano-antennas. By incorporating plasmonic nano-antennas, stronger dipole moments are induced in response to an incident optical pump beam and, therefore, higher optical-to-terahertz conversion efficiencies are achieved compared to the state-of-the art. We demonstrate terahertz radiation power levels as high as 300 µW over a 0.1–5 THz frequency range at a 400 mW optical pump power. This is the highest reported terahertz radiation power level from a photoconductive terahertz emitter operating at telecommunication optical pump wavelengths.

A novel heterodyne terahertz detector is presented that replaces terahertz mixer and local oscillator of conventional heterodyne terahertz detectors with a plasmonic photomixer pumped by an optical local oscillator. The optical local oscillator consists of two wavelength-tunable continuous-wave optical sources with a terahertz frequency difference. As a result, detection bandwidth and sensitivity of the presented heterodyne terahertz detector is not limited by radiation frequency and power restrictions of conventional terahertz sources. We demonstrate a first proof-of-concept heterodyne detector prototype designed for operation at 0.1 THz frequency range, which offers dynamic ranges as high as 70 dB.

We present a high-performance terahertz radiation source based on a photomixer integrated with a logarithmic spiral antenna that utilizes plasmonic contact electrodes to offer record-high continuous-wave terahertz radiation powers. Use of plasmonic contact electrodes allows increasing terahertz photocurrents fed to the antenna, resulting in significantly higher terahertz radiation power levels compared to conventional photomixers. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a radiation power of 17 µW at 1 THz, exhibiting a 3-fold higher radiation power level compared to the state-of-the art.

Research conducted in parallel with the construction of various vacuum electronic devices, including a 220 GHz Sheet Beam Traveling Wave Tube (SBTWT), a 263 GHz SBTWT, and two 346 GHz Backward Wave Oscillators (BWOs), has demonstrated that data garnered from the manufacturing process helps improve the performance, reduce the time to build, and lower the cost of subsequent devices. The data collected from metrology, microscopy, and manufacturing control are also critical to improving future device builds and provide powerful insight into the nature of fabricating high performance vacuum electronics.

There is a region called “Terahertz Gap” between the highest frequency of microwave technology and the lowest frequency of photonic technology. At this region, the device development has been one of major issues on R&D. Recently, vacuum electronics devices, especially as high power RF sources, hold the potential for innovational progress in various applications. We report the development activity of terahertz amplifiers with folded waveguide traveling wave tube (TWT) in this region.

In this report, we present a novel approach to exploit the nonlinear response of terahertz (THz) field allowing the observation of ionization phenomenon in a single metal nano island. Because it is not easy to access such high power THz source to generate field over the threshold of the materials, fundamental studies on nonlinear terahertz waves and their applications in spectroscopy have been limited thus far. We are able to overcome this limitation through the use of a metallic nano island embedded in a slot antenna which strongly confines the terahertz electric field driving the system into a highly nonlinear regime. The structure, composed of a nano slot antenna and a nano island located at the center, highly confines THz electromagnetic field at the center of the structure, resulting in huge field enhancement by orders of magnitude at a specific frequency. Electrons on a metallic surface experience a ponderomotive force in a highly confined and enhanced THz electric field directed towards the weak field area by a field gradient. As a result, the accelerated electrons acquire enough energy to ionize ambient carbon atoms. It has to be stressed that it is the first time to observe the ionization of atoms induced by the enhanced terahertz radiation.

Time-domain spectroscopy using coherent millimeter and sub-millimeter radiation (also known as terahertz radiation) is rapidly expanding its application, owing greatly to the remarkable advances in generating and detecting such radiation. However, many current techniques for coherent terahertz detection have limited dynamic range, thus making it difficult to perform some basic experiments that need to directly compare strong and weak terahertz signals. Here, we propose and demonstrate a novel technique based on cross-polarized spectral-domain interferometry to achieve ultra-high dynamic range electro-optic sampling measurement of coherent millimeter and sub-millimeter radiation. In our scheme, we exploit the birefringence in a single-mode polarization maintaining fiber in order to measure the phase change induced by the electric field of terahertz radiation in the detection crystal. With our new technique, we have achieved a dynamic range of 7 × 106, which is 4 orders of magnitude higher than conventional electro-optic sampling techniques, while maintaining comparable signal-to-noise ratio. The present technique is foreseen to have great impact on experiments such as linear terahertz spectroscopy of optically thick materials (such as aqueous samples) and nonlinear terahertz spectroscopy, where the higher dynamic range is crucial for proper interpretation of experimentally obtained results.

We present the design, numerical simulations and experimental measurements of an asymmetric cross terahertz metamaterial absorber (MPA) on ultra-flexible polyimide film. The perfect metamaterial absorber composed of two structured metallic layers separated with a polyimide film with a total thickness of functional layers much smaller than the operational wavelength. Two distinct absorption peaks are found at resonance frequencies of 0.439THz and 0.759 THz with resonance amplitude of near unity, which are in good agreement with the simulation results. The sample is also measured by a THz-TDS imaging system to illustrate the absorption characterization. The scanning images show that the sample could act as a perfect absorber at specific resonance frequencies while a perfect reflector at off resonance frequencies. To illustrate the physical mechanism behind these spectral responses, the distribution of the power loss and surface current are also presented. The result shows that the incident wave is trapped and absorbed by the polyimide dielectric layer at different vicinities of the proposed asymmetric cross MPA for the two absorption peaks. Furthermore, the index sensing performance of the structure is also investigated, and the calculated sensitivity is 90GHz/RIU for f1 mode and 154.7GHz/RIU for f2 mode, indicating that the higher frequency resonance absorption peak has better potential applications in sensing and detection. The ultra-flexible, low cost, high intensity dual band terahertz absorbers may pave the way for designing various terahertz functional devices, such as ultrasensitive terahertz sensors, spatial light modulators and filters.

The terahertz (THz) band of the electromagnetic spectrum, with frequencies ranging from 300 GHz to 3 THz, has attracted wide interest in recent years owing to its potential applications in numerous areas. Significant progress has been made toward the development of devices capable of actively controlling terahertz waves; nonetheless, further advances in device functionality are necessary for employment of these devices in practical terahertz systems. Here, we demonstrate a low voltage, sharp switching terahertz modulator device based on metamaterials integrated with metal semiconductor metal (MSM) varactors, fabricated on an AlGaAs/InGaAs based heterostructure. By varying the applied voltage to the MSM-varactor located at the center of split ring resonator (SRR), the resonance frequency of the SRR-based metamaterial is altered. Upon varying the bias voltage from 0 V to 3 V, the resonance frequency exhibits a transition from 0.52 THz to 0.56 THz, resulting in a modulation depth of 45 percent with an insertion loss of 4.3 dB at 0.58 THz. This work demonstrates a new approach for realizing active terahertz devices with improved functionalities.

Multi-spectral imaging systems typically require the cumbersome integration of disparate filtering materials and detectors in order to operate simultaneously in multiple spectral regions. Each distinct waveband must be detected at different spatial locations on a single chip or by separate chips optimised for each band. Here, we report on a single component that optically multiplexes visible, Mid Infrared (4.5 μm) and Terahertz (126 μm) radiation thereby maximising the spectral information density. We hybridise plasmonic and metamaterial structures to form a device capable of simultaneously filtering 15 visible wavelengths and absorbing Mid Infrared and Terahertz. Our synthetic multi-spectral component could be integrated with silicon complementary metal-oxide semiconductor technology where Si photodiodes are available to detect the visible radiation and micro-bolometers available to detect the Infrared/Terahertz and render an inexpensive, mass-producible camera capable of forming coaxial visible, Infrared and Terahertz images.

A scheme to generate terahertz wave based on optical quadrupled frequency technique is simulated and tested.0.12THz terahertz wave is generated from 30GHz microwave source.

A newly introduced computationally-efficient FDTD model of pulse propagation in photonic crystal fibers, which accounts for both mode dispersion and third-order nonlinear properties of applied materials, is used in this paper to the study of the electrodynamics of terahertz generation with four-wave mixing of two co-propagating femtosecond pulses. Basic requirements for efficient conversion of energy, related to such parameters like group velocity dispersion, are specified. The impact of the transmission line characteristics and pulse properties on both spectral and time evolution of the generated terahertz radiation are shown and discussed. The obtained results pave the way for further rigorous studies heading toward bridging a terahertz gap with the aid of broadly available high-power femtosecond laser sources supplemented with dispersion-engineered photonic crystal fibers.

By using nano-electrodes, the THz emission power was improved by four times and more than 50 times for the pulse and continuous-wave terahertz emitter. Comparisons are made in terms of local carrier dynamics.

The terahertz frequency range, often referred to as the “terahertz” gap, lies wedged between microwave at the lower end and infrared at the higher end of the spectrum, occupying frequencies between 0.3 and 3.0 THz. For a long time, applications in THz frequencies had been limited to astronomy and chemical sciences, but with advancements in THz technology in recent years, it has shown great promise in a wide range of applications ranging from security screening for concealed weapons and contraband detection to global environmental monitoring, nondestructive quality control, and ultra-fast wireless communication. Up until recently, the terahertz frequency range has been mostly addressed by high-mobility compound III-V processes, expensive nonlinear optics, or cryogenically cooled quantum cascade lasers. A low-cost, room temperature alternative can enable the development of such a wide array of applications, not currently accessible due to cost and size limitations. In this thesis, we will discuss our approach towards development of integrated terahertz technology in silicon-based processes. In the spirit of academic research, we will address frequencies close to 0.3 THz as “terahertz.” In this chapter, we address both fronts of integrated THz systems in silicon: THz power generation, radiation and transmitter systems, and THz signal detection and receiver systems. THz power generation in silicon-based integrated circuit technology is challenging due to lower carrier mobility, lower cut-off frequencies compared to compound III-V processes, lower breakdown voltages, and lossy passives. Radiation from silicon chips is also challenging due to lossy substrates and the high dielectric constant of silicon. In this chapter, we will describe novel ways of combining circuit and electromagnetic techniques in a holistic design approach, which can overcome limitations of conventional block-by-block or partitioned design methodology, in order to generate high-frequency signals above the classical definition of cut-off frequencies (ft/fmax). We demonstrate this design philosophy in an active electromagnetic structure, which we call distributed active radiator. It is inspired by an inverse electromagnetic (EM) approach, where instead of using classical circuit and electromagnetic blocks to generate and radiate THz frequencies, we formulate surface (metal) currents in silicon chips for a desired THz field profile and develop active means of controlling different harmonic currents to perform signal generation, frequency multiplication, radiation and lossless filtering, simultaneously in a compact footprint. By removing the artificial boundaries between circuits, electromagnetics, and antenna, we open ourselves to a broader design space. This enabled us to demonstrate the first 1-mW effective-isotropic-radiated-power (EIRP) THz (0.29 THz) source in CMOS with total radiated power being three orders of magnitude more than previously demonstrated. We also proposed a near-field synchronization mechanism, which is a scalable method of realizing large arrays of synchronized autonomous radiating sources in silicon. We also demonstrate the first THz CMOS array with digitally controlled beam-scanning in 2D space with radiated output EIRP of nearly 10 mW at 0.28 THz.

China is planning to build a 5m THz telescope (DATE5) at Dome A, Antarctic, with two operation bands centered at 0.85THz and 1.4THz. This paper introduces mainly the development of ultra-sensitive superconducting detectors for the DATE5, including a 0.85-THz superconductor-insulator-superconductor (SIS) mixer, a 1.4-THz hot-electron bolometer (HEB) mixer, and a terahertz superconducting imaging array.

Photoconductive antenna on LTG-GaAs has been simulated and fabricated. Reducing gap size, increasing bias voltage and increasing laser pulse power will increase terahertz field. Narrower laser pulse width results in wider terahertz bandwidth.

In this paper we demonstrate a self coherent terahertz system implemented in a standard a 65 nm CMOS technology for displacement sensing application. We name this method retroactive detection since no additional terahertz components are required to operate. The device main operating frequency is 0.35 THz in continuous-wave mode and operates at room temperature.

Isolators, or optical diodes, are devices enabling unidirectional light propagation by using non-reciprocal optical materials, namely materials able to break Lorentz reciprocity. The realization of isolators at terahertz frequencies is a very important open challenge made difficult by the intrinsically lossy propagation of terahertz radiation in current non-reciprocal materials. Here we report the design, fabrication and measurement of a terahertz non-reciprocal isolator for circularly polarized waves based on magnetostatically biased monolayer graphene, operating in reflection. The device exploits the non-reciprocal optical conductivity of graphene and, in spite of its simple design, it exhibits almost 20 dB of isolation and only 7.5 dB of insertion loss at 2.9 THz. Operation with linearly polarized light can be achieved using quarter-wave plates as polarization converters. These results demonstrate the superiority of graphene with respect to currently used terahertz non-reciprocal materials and pave the way to a novel class of optimal non-reciprocal devices., Optical isolators, or optical diodes, allow electromagnetic radiation to travel in one direction but not the other. Here, the authors achieve unidirectional propagation of terahertz waves by taking advantage of the non-reciprocal nature of optical conductivity in magnetostatically biased graphene.

Remarkable progress in terahertz (THz) sources and detectors is followed by the necessity of manipulating of terahertz radiation. Since natural materials can not perform efficient interaction with THz radiation, artificial structures called metamaterials are designed to overcome “THz gap” in this area. A variety of tunable metamaterials using different methods of control are presented and discussed in this review paper.

Anyone hoping to exploit this promising region of the electromagnetic spectrum must confront its very daunting physics. Wirelessly transfer huge files in the blink of an eye! Detect bombs, poison gas clouds, and concealed weapons from afar! Peer through walls with T-ray vision! You can do it all with terahertz technology-or so you might believe after perusing popular accounts of the subject.

Significant advances in the development of millimeter-wave and terahertz (30-10 000 GHz) technologies have been made to cope with the increasing interest in this still not fully explored electromagnetic spectrum. The nature of electromagnetic waves over this frequency range is well suited for the development of high-resolution imaging applications, molecular-sensitive spectroscopic devices, and ultrabroadband wireless communications. In this paper, millimeter-wave and terahertz antenna technologies are overviewed including the conventional and nonconventional planar/nonplanar antenna structures based on different platforms. As a promising technological platform, substrate-integrated circuits (SICs) attract more and more attention. Various substrate-integrated waveguide (SIW) schemes and other synthesized guide techniques have been widely employed in the design of antennas and arrays. Different types of substrate-integrated antennas and beamforming networks are discussed with respect to theoretical and experimental results in connection with electrical and mechanical performances.

Terahertz technology has recently emerged as a highly sought-after and versatile scientific tool in many fields, including medical imaging, security screening, and wireless communication. However, scientific progress has been hindered by the lack of sources and detectors in this frequency range, thereby known as the terahertz gap. Here, we show that carbon nanotube quantum dots coupled to antennas are extremely sensitive, broad-band, terahertz quantum detectors with spectral resolution. Their response is due to photon-assisted single-electron tunneling and it is substantially enhanced by a novel radiation-induced nonequilibrium cooling of the electrons, causing a sharp height increase of the Coulomb oscillation peaks.

Indium nitride is a novel narrow band gap semiconductor. The material is a potential strong source of terahertz frequency electromagnetic radiation with applications in time-domain terahertz spectroscopy and imaging systems. This article reviews recent experimental research on terahertz emission from the binary compound semiconductor indium nitride excited by near-infrared laser beams or microseconds electrical pulses. Advantages of indium nitride as terahertz radiation source material are discussed. It is demonstrated that different mechanisms contribute to the emission of terahertz radiation from indium nitride. The emission of up to 2.4 μW of THz radiation power is observed when InN is excited with near-infrared femtosecond laser pulses at an average power of 1 W.

There is currently a great deal of interest in the development of efficient compact sources of terahertz (THz) radiation. There are many factors of device and materials design which are still under ongoing improvement with the aim of producing an efficient, high power, room-temperature THz signal emission device which is tunable over a practical THz frequency range. The recent advances in production of various room-temperature THz radiation sources are reviewed with particular emphasis on photomixer antenna devices, and recent patents on technology and methods relating to: pulsed and continuous wave (CW) THz generation via nonlinear crystals; quantum cascade lasers (QCLs); ultrafast diodes and photodiodes; and heterodyne sources are discussed.

In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thin-film sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy.

Through the ionization process, the very air that we breath is capable of generating terahertz (THz) electromagnetic field strengths greater than 1 MV/cm, useful bandwidths of over 100 THz, and highly directional emission patterns. Following the ionization of air, the emitted air-plasma fluorescence or acoustics can serve as an omnidirectional, broadband, THz wave sensor. Here we review significant advances in laser air photonics that help to close the “THz gap,” enabling ultra-broadband THz wave generation and detection, for applications including materials characterization and non-destructive evaluation. The feasibility for remote sensing, as well as the remaining challenges and future opportunities are also discussed.

We design and demonstrate a flexible, ultrathin and double-sided metamaterial perfect absorber (MPA) at 2.39 terahertz (THz), which enables excellent light absorbance under incidences from two opposite sides. Herein, the MPA is fabricated on a λ0/10.1-thick flexible polyethylene terephthalate substrate of εr = 2.75 × (1 + 0.12i), sandwiched by two identical randomized metallic patterns by our stochastic design process. Such an MPA provides tailored permittivity and permeability to approach the impedance of free space for minimizing reflectance and a great imaginary part of the refractive index for reducing transmittance and finally results in high absorbance. Both experimental measurement and numerical simulation are in a good agreement. The flexible, ultrathin and double-sided MPA significantly differs from traditional quarter-wavelength absorbers and other single-sided perfect absorbers, paving a way toward practical THz applications in thermal emission, sensing and imaging, communications, stealth technique and even energy harvesting.

Superconductivity derives its most salient features from the coherence of its macroscopic wave function. The associated physical phenomena have now moved from exotic subjects to fundamental building blocks for quantum circuits such as qubits or single photonic modes. Here, we theoretically find that the AC Josephson effect---which transforms a DC voltage $V_b$ into an oscillating signal $cos(2eV_b t/ \hbar)$---has a mesoscopic counterpart in normal conductors. We show that on applying a DC voltage $V_b$ to an electronic interferometer, there exists a universal transient regime where the current oscillates at frequency $eV_b/h$. This effect is not limited by a superconducting gap and could, in principle, be used to produce tunable AC signals in the elusive $0.1-10$ THz "terahertz gap"., Comment: 4 pages, 2 figures, 5 equations

An equivalent circuit model was used to analyze a symmetrical complementary metamaterial for resonant filtering characteristic at terahertz frequencies. Using terahertz time-domain spectroscopy system, we examined the transmittance spectra for the metamaterial structure. The experimental results validate those of the theoretical predictions. The structure could lead to be a terahertz wave bandpass filter with a narrow transmission bandwidth centered at 2.01 THz and very sharp edges. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 54:351–354, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26548

The overall purpose of this paper is the prediction of the ultimate electrical high-frequency performance potential for SiGeC HBTs under the constraints of practical applications. This goal is achieved by utilizing advanced device simulation tools with parameters calibrated to experimental results of most advanced existing technologies. In addition, detailed electrostatic and electrothermal simulations are performed for determining the parasitic capacitances, temperature increase, and safe operating area of aggressively scaled devices. The important figures of merit are then determined from circuit simulation employing an accurate compact model incorporating all relevant physical effects. Based on the vertical profile found in Part I, this paper focuses on achieving a balanced device design by lateral scaling. It is shown that the peak values of (fT, fmax) around (1, 1.5) THz may be achievable. Such a performance limit provides still significant headroom for further developing existing processes and makes SiGeC HBTs well-suitable for highly integrated millimeter-wave applications operating within the low-end of the terahertz gap.

We present a multimode continuous wave terahertz spectrometer driven by a compact laser diode with a tunable spectrum. An external feedback based on two optical gratings into the diode allows us to shape the laser emission spectrum, and hence the temporal shape of the terahertz signals. In particular, we show a power enhancement of a factor of ten for individual regions of the spectrum to gain a signal-to-noise ratio in the frequency range of interest.

Nanotechnologies promise new solutions for several applications in the biomedical, industrial and military fields. At the nanoscale, a nanomachine is considered as the most basic functional unit which is able to perform very simple tasks. Communication among nanomachines will allow them to accomplish more complex functions in a distributed manner. In this paper, the state of the art in molecular electronics is reviewed to motivate the study of the Terahertz Band (0.1-10.0 THz) for electromagnetic (EM) communication among nano-devices. A new propagation model for EM communications in the Terahertz Band is developed based on radiative transfer theory and in light of molecular absorption. This model accounts for the total path loss and the molecular absorption noise that a wave in the Terahertz Band suffers when propagating over very short distances. Finally, the channel capacity of the Terahertz Band is investigated by using this model for different power allocation schemes, including a scheme based on the transmission of femtosecond-long pulses. The results show that for very short transmission distances, in the order of several tens of millimeters, the Terahertz channel supports very large bit-rates, up to few terabits per second, which enables a radically different communication paradigm for nanonetworks.

An integrated terahertz radiation sensor based on apodized and chirped with apodization open resonance microstructures is proposed. It is shown that by choosing the structure and optimizing its structural parameters one can obtain a simple compact receiver of terahertz radiation with an electromagnetic wave conversion efficiency of 91.23% in the 0.55–0.78 THz spectral range.

If we credit the integrated circuit with one thing, it should be the taming of the electromagnetic spectrum. If you want to create or capture visible photons, there are plenty of compact devices to choose from, incorporating everything from miniature photodiodes and lasers to LEDs and slim charge-coupled devices. And if you want to pick up or send a radio signal, there are a staggering number of receivers, transmitters, and antennas to suit your needs. But the IC hasn't conquered every bit of the spectrum, and one region stands out: the terahertz frontier, a range that extends from the highest frequency radio waves to the lowest frequency infrared light. Over the decades, engineers have made many attempts to create compact, solidstate devices that can harness it, but terahertz radiation has proven particularly tricky to use.

New and emerging terahertz technology applications make this a very exciting time for the scientists, engineers, and technologists in the field. New sensors and detectors have been the primary driving force behind the unprecedented progress in terahertz technology, but in the last decade extraordinary developments in terahertz sources have also occurred. Driven primarily by space based missions for Earth, planetary, and astrophysical science, frequency multiplied sources have dominated the field in recent years, at least in the 2-3 THz frequency range. More recently, over the past few years terahertz quantum cascade lasers (QCLs) have made tremendous strides, finding increasing applications in terahertz systems. Vacuum electronic devices and photonic sources are not far behind either. In this article, the various technologies for terahertz sources are reviewed, and future trends are discussed.

Terahertz time-domain spectroscopy accesses the frequency range between 100 GHz and 5 THz by using the coherent generation and detection based on femtosecond laser sources. On the way to obtain fingerprint absorption spectra of molecular solids, terahertz waveguides have proven to be a valuable tool to extend the results to narrow and high resolution linewidths of crystalline solids. We will discuss the development, properties and applications of terahertz waveguide geometries for spectroscopic applications, in particular high-resolution measurements using parallel-plate waveguides.

Nonlinear optical terahertz wave generation is a promising method for realizing a practical source with wide frequency range and high peak power. Unfortunately, many nonlinear crystals have a strong absorption in the terahertz frequency region. This limits efficient and widely tunable terahertz wave generation. The Cherenkov phase-matching method is one of the most promising techniques for overcoming these problems. We propose a prism-coupled Cherenkov phase-matching method, in which a prism with a suitable refractive index at terahertz frequencies is coupled to a nonlinear crystal. We demonstrate prism-coupled Cherenkov phase-matching terahertz generation using the DAST and LiNbO3 crystals. With a DAST crystal, we obtain a spectral flat tunability up to 10 THz by difference frequency generation. With a LiNbO3 crystal, we observe a spectral flat broadband terahertz pulse generation up to 5 THz pumped by a femto second fiber laser. The obtained temporal waveform is an ideal half cycle pulse suitable for reflection terahertz tomography.