Hundreds Of GHz Research Articles

Solar Radio Emissions

The radio emission from the Sun covers a very wide frequency band ranging from several hundreds of GHz (sub-millimeter wavelength) down to sub-MHz (kilometer wavelength) [...]

Spin-vertical-cavity surface-emitting lasers with by-design-defined birefringence for high-speed modulation.

We propose a new, to the best of our knowledge, type of spin-vertical-cavity surface-emitting laser (VCSEL) with controlled by design birefringence. To this aim, we utilize the so-called columnar thin films (CTFs) in the VCSEL dielectric distributed Bragg mirror and/or in a second dielectric cavity. We design such CTF-VCSELs with pre-defined birefringence and calculate their polarization-resolved resonant longitudinal modes and the corresponding quantum-well confinement factors and threshold gains. Using the spin-flip VCSEL model, we show that such spin CTF-VCSELs can achieve small-signal modulation response with a 3 dB cutoff frequency of several hundreds of GHz.

Toward Practical Superconducting Accelerators for Machine Learning Using U-SFQ

Most popular superconducting circuits operate on information carried by ps-wide, μV-tall, single flux quantum (SFQ) pulses. These circuits can operate at frequencies of hundreds of GHz with orders of magnitude lower switching energy than complementary-metal-oxide-semiconductors (CMOS). However, under the stringent area constraints of modern superconductor technologies, fully-fledged, CMOS-inspired superconducting architectures cannot be fabricated at large scales. Unary SFQ (U-SFQ) is an alternative computing paradigm that can address these area constraints. In U-SFQ, information is mapped to a combination of streams of SFQ pulses and in the temporal domain. In this work, we extend U-SFQ to introduce novel building blocks such as a multiplier and an accumulator. These blocks reduce area and power consumption by 2\(\times\)and 4\(\times\)compared with previously proposed U-SFQ building blocks and yield at least 97% area savings compared with binary approaches. Using these multiplier and adder, we propose a U-SFQ Convolutional Neural Network (CNN) hardware accelerator capable of comparable peak performance with state-of-the-art superconducting binary approach (B-SFQ) in 32\(\times\)less area. CNNs can operate with 5–8 bits of resolution with no significant degradation in classification accuracy. For 5 bits of resolution, our proposed accelerator yields 5\(\times\)to 63\(\times\)better performance than CMOS and 15\(\times\)to 173\(\times\)better area efficiency than B-SFQ.

Ultrafast acousto-optic modulation at the near-infrared spectral range by interlayer vibrations

Abstract The acousto-optic modulation over a broad near-infrared (NIR) spectrum with high speed, excellent integrability, and relatively simple scheme is crucial for the application of next-generation opto-electronic and photonic devices. This study aims to experimentally demonstrate ultrafast acousto-optic phenomena in the broad NIR spectral range of 0.77–1.1 eV (1130–1610 nm). Hundreds of GHz of light modulation are revealed in an all-optical configuration by combining ultrafast optical spectroscopy and light–sound conversion in 10–20 nm-thick bismuth selenide (Bi2Se3) van der Waals thin films. The modified optical transition energy and the line shape in the NIR band indicate phonon–photon interactions, resulting in a modulation of optical characteristics by the photoexcited interlayer vibrations in Bi2Se3. This all-optical, ultrafast acousto-optic modulation approach may open avenues for next-generation nanophotonic applications, including optical communications and processing, due to the synergistic combination of large-area capability, high photo-responsivity, and frequency tunability in the NIR spectral range.

Towards 2-μm comb light source based on multiple four-wave mixing in a dual-frequency Brillouin fiber laser

In this study, we report the generation of multi-wavelength light sources through enhanced four-wave-mixing processes using a straightforward and adaptable dual-frequency Brillouin fiber laser. This passive optical and nonreciprocal cavity is first tested and analyzed with long fiber lengths up to 1 km in the 1.55 μm telecommunication C band and then in the 2-μm waveband. In the latter case, we demonstrate that our fiber cavity enables efficient multiple four-wave mixings, in the continuous-wave regime, which are commonly inaccessible in long silica-fibers due to increased losses. We also report on the tunable repetition rate from tens of GHz to hundreds of GHz, by simply changing the frequency spacing between the two continuous-wave pumps. The coherence limitations of our all-fiber system are discussed, along with the impact of the dispersion regime of the nonlinear fiber that forms the cavity.

Slot-Waveguide Based All-Optical RF Spectrum Analyzer

All-optical radio-frequency spectrum analyzers (AORFSAs) with ultrabroad bandwidth break the electronic bottleneck and provide an efficient frequency analysis means for ultrafast optical signals in communications, signal generation and processing systems. Here, we propose and experimentally demonstrate an AORFSA built on the cross-phase modulation effect in a 50 cm long CMOS-compatible photonic slot-waveguide. The waveguide has a 100 nm thick thin-film core of fused silica that is sandwiched by two 750 nm thick cladding layers of high-index doped silica, which shows optimized dispersion and comparable nonlinear characteristics. The measured 3 dB bandwidth of the proposed slot-waveguide-based AORFSA has a three-fold increase over the conventional channel waveguide having the same dimension and length. The sensitivity and wavelength- and polarization-dependence properties are investigated, confirming the proposed waveguide as a versatile platform for frequency analysis of ultrafast optical signals, such as Kerr microcombs with hundreds of GHz or even THz mode spacing.

Liquid-Crystal Spin-VCSEL with Electro-Optically Controllable Birefringence

We suggest a new construction of spin-VCSEL with an embedded nematic liquid crystal (LC) in a second cavity. We design such a coupled-cavity LC-VCSEL and develop a procedure for calculating its LC-voltage dependent polarization resolved resonant longitudinal modes and their quantum-well confinement factors. Using these characteristics, we are able to slightly modify the spin-flip VCSEL model to include the voltage dependent birefringence and anisotropy. Then, we show that such an LC-VCSEL can reach small signal modulation response with a 3dB cut off frequency of several hundreds of GHz.

Особенности пробоя тяжелых инертных газов в сфокусированном пучке излучения Новосибирского лазера на свободных электронах

The results of experimental studies on the breakdown of noble gases (argon and krypton) by terahertz radiation from the Novosibirsk free electron laser (NovoFEL) are presented. For the first time, the breakdown thresholds of noble gases by terahertz radiation were measured in a wide pressure range (0.2 – 1.5 bar). Previous experiments to measure breakdown thresholds in the THz range in various gases were carried out for hundreds of GHz or at atmospheric pressure. Experimental breakdown thresholds are compared with calculated data using various simplified models.

Features of the breakdown in heavy noble gases under the action of Novosibirsk free electron laser radiation

The results of experimental studies on the breakdown of noble gases (argon and krypton) by terahertz radiation from the Novosibirsk free electron laser (NovoFEL) are presented. For the first time, the breakdown thresholds of noble gases by terahertz radiation were measured in a wide pressure range (0.2-1.5 bar). Previous experiments to measure breakdown thresholds in the THz range in various gases were carried out for hundreds of GHz or at atmospheric pressure. Experimental breakdown thresholds are compared with calculated data using various simplified models. Keywords: THz radiation, gas breakdown, THz laser discharge.

Resonant phonon-magnon interactions in freestanding metal-ferromagnet multilayer structures

We analyze resonant magneto-elastic interactions between standing perpendicular spin wave modes (exchange magnons) and longitudinal acoustic phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all metal layers control the frequencies and eigenmodes of acoustic vibrations. The here proposed design allows for achieving and tuning the spectral and spatial modes overlap between phonons and magnons that results in their strong resonant interaction. Realistic simulations for gold-nickel multilayers show that sweeping the external magnetic field should allow for observing resonantly enhanced interactions between individual magnon and phonon modes in a broad range of frequencies spanning from tens of GHz up to several hundreds of GHz, which can be finely tuned through the multilayer design. Our results would enable the systematic study and the deep understanding of resonantly enhanced magneto-elastic coupling between individual phonon and magnon modes up to frequencies of great contemporary fundamental and applied interest.

High-Performance All-Optical Modulator Based on Graphene-HBN Heterostructures

Graphene has emerged as an ultrafast photonic material for on-chip all-optical modulation. However, its atomic thickness limits its interaction with guided optical modes, which results in a high switching energy per bit or low modulation efficiencies. Nonetheless, it is possible to enhance the interaction of guided light with graphene by nanophotonic means. Herein, we present a practical design of an all-optical modulator that is based on graphene and hexagonal boron nitride (hBN) heterostructures that are hybrid integrated into silicon slot waveguides. Using this device, a high extinction ratio (ER) of 7.3 dB, an ultralow insertion loss (IL) of <0.6 dB, and energy-efficient switching (<0.33 pJ/bit) are attainable for a 20{\mu}m long modulator with double layer graphene. In addition, the device performs ultrafast switching with a recovery time of <600 fs, and could potentially be employed as a high-performance all-optical modulator with an ultra-high bandwidth in the hundreds of GHz. Moreover, the modulation efficiency of the device is further enhanced by stacking additional layers of graphene-hBN heterostructures, while theoretically maintaining an ultrafast response. The proposed device exhibits highly promising performance metrics, which are expected to serve the needs of next-generation photonic computing systems.

Room temperature plasmonic graphene hot electron bolometric photodetectors: A comparative analysis

The performance of a recently proposed integrated graphene-bolometric photodetector is assessed. The responsivity of hundreds of A/W and speed on the scale of hundreds of GHz are predicted. The impressive performance is attributed to the small length over which the energy is absorbed by graphene. The short length leads to a highly enhanced energy density, which causes the increase of the electron temperature in graphene. The model has been validated against recently published experimental results from high-speed graphene photodetectors and found to be in good agreement.

Survey of Exposure to RF Electromagnetic Fields in the Connected Car

Future vehicles will be increasingly connected to enable new applications and improve safety, traffic efficiency and comfort, through the use of several wireless access technologies, ranging from vehicle-to-everything (V2X) connectivity to automotive radar sensing and Internet of Things (IoT) technologies for intra-car wireless sensor networks. These technologies span the radiofrequency (RF) range, from a few hundred MHz as in intra-car network of sensors to hundreds of GHz as in automotive radars used for in-vehicle occupant detection and advanced driver assistance systems. Vehicle occupants and road users in the vicinity of the connected vehicle are thus daily immersed in a multi-source and multi-band electromagnetic field (EMF) generated by such technologies. This paper is the first comprehensive and specific survey about EMF exposure generated by the whole ensemble of connectivity technologies in cars. For each technology we describe the main characteristics, relevant standards, the application domain, and the typical deployment in modern cars. We then extensively describe the EMF exposure scenarios resulting from such technologies by resuming and comparing the outcomes from past studies on the exposure in the car. Results from past studies suggested that in no case EMF exposure was above the safe limits for the general population. Finally, open challenges for a more realistic characterization of the EMF exposure scenario in the connected car are discussed.

Importance of Probe Choice for Extracting Figures of Merit of Advanced mmW Transistors

The measurement of the figures of merit (FOMs) of an advanced and miniaturized transistor becomes a challenge when its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {MAX}}$ </tex-math></inline-formula> goes above many hundreds of GHz. In fact, the quantities to be measured become smaller and smaller and thus the influence of the measurement environment becomes less and less negligible. Indeed, when measuring the same test structures using two different renowned commercial probes having a different topology, a “signature” of each probe can been observed, in particular, when plotting <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {U} \times \text {freq}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${U}$ </tex-math></inline-formula> is the Mason gain) as a function of frequency, which is usually carried out for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {MAX}}$ </tex-math></inline-formula> estimation. For millimeter wave (mmW) technologies, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {MAX}}$ </tex-math></inline-formula> is the key FOM for benchmarking technologies, thus it becomes urgent to clarify this measurement. In this work, we give a proof that measurement becomes probe dependent. We constructed an accurate electromagnetic (EM) model of each probe using X-ray tomography and thus simulated the measurement environment at close proximity of the wafer using EM and SPICE simulation. Hence, each signature of the probe is clearly reproduced by the simulation, highlighting that the unexpected result is not due to an inaccuracy done by the user such as probe positioning or to a limitation of the vector network analyzer (VNA) but is the result of the unwanted coupling between the probe and the substrate or between probes and the inability of the short open load thru (SOLT) and on-wafer thru reflect line (TRL) calibration algorithms to completely remove these couplings.

All-graphene perfect broadband THz absorber

By combining the 3D printing, electroplating and chemical vapor deposition processes we fabricated “bubble wrap” polymer nanomembrane covered with multilayered graphene. Such a metasurface composed of array of graphene hemispheres shows extremely broadband and almost perfect absorption in terahertz (THz)22Abbreviations: THz – Terahertz, EM – electromagnetic, CVD – chemical vapor deposition, PMMA – poly-methyl methacrylate. frequency range being robust against macroscopic structural defects including holes and volcanic-like hats on hemispherical metaatoms. The developed theory perfectly explains our experimental findings including virtual independence of the metasurface transmittivity, reflectivity and absorptivity on the angle of incidence in terms of the plasmon dark mode formation. Our approach enables the THz perfect absorber that covers a frequency range spanning from few hundreds of GHz to 1.2 THz, and even more, while the proposed fabrication technique can also be employed in numerous applications that require free standing corrugated graphene/polymer nanomembranes.

Breaking Space Inversion‐Symmetry to Obtain Asymmetric Spin‐Wave Excitation in Systems with Nonuniform Magnetic Exchange

AbstractThe consequences of non‐uniform exchange in magnetic systems are reported. The quantum mechanical exchange interaction between spins is responsible for the phenomenon of magnetic order, and is generally considered to be uniform across bulk magnetic systems. Partly inspired by the Dzyaloshinskii‐Moriya interaction—also known as antisymmetric exchange—a linearly varying exchange interaction is used along a magnetic strip as a route to spatial inversion symmetry‐breaking. It is found that, in addition to asymmetric modes and localization, spatially varying exchange can be used to design nonreciprocal magnetic signal excitation at frequencies that are tunable. Moreover, the authors’ work predicts nonreciprocity to occur across a vast range of frequencies up to hundreds of GHz. Such spin wave engineering is a key area of ongoing research in the fields of magnonics and spintronics, which are expected to enable the next generation of wireless communication technology and information processing. Analogous nonreciprocity is expected to occur in other wave systems with gradient properties.

A versatile experimental testbed for ultrabroadband communication networks above 100 GHz

Communication at terahertz (THz) frequencies is envisioned as a near-future landmark in wireless networking and a key component of the sixth generation (6G) wireless systems and beyond. In the last decade, major progress has happened in terms of device technology development as well as THz-wave propagation and channel modeling. In order to advance THz communication and networking research, there is tremendous necessity in developing programmable software-defined hardware and architectures that operate at THz frequencies and are able to process signals with tens to hundreds of GHz of bandwidth, thus making most out of moving to THz band. This paper presents a versatile testbed for conducting wireless experimental research above 100 GHz. The platform consists of multiple sets of analog front-ends at three different frequencies between 100 GHz and 1 THz as well as three different digital signal processing back-ends, able to manipulate more than 10 GHz of bandwidth in real-time. Implementation details and early experimental results to demonstrate the platform capabilities are presented.

Methodological investigation into the noise influence on nanolasers' large signal modulation.

Nanolasers are considered ideal candidates for communications and data processing at the chip-level thanks to their extremely reduced footprint, low thermal load and potentially outstanding modulation bandwidth, which in some cases has been numerically estimated to exceed hundreds of GHz. The few experimental implementations reported to date, however, have so-far fallen very short of such predictions, whether because of technical difficulties or of overoptimistic numerical results. We propose a methodology to study the physical characteristics which determine the system's robustness and apply it to a general model, using numerical simulations of large-signal modulation. Changing the DC pump values and modulation frequencies, we further investigate the influence of intrinsic noise, considering, in addition, the role of cavity losses. Our results confirm that significant modulation bandwidths can be achieved, at the expense of large pump values, while the often targeted low bias operation is strongly noise- and bandwidth-limited. This fundamental investigation suggests that technological efforts should be oriented towards enabling large pump rates in nanolasers, whose performance promises to surpass microdevices in the same range of photon flux and input energy.

Ultrafast Quantum-Well Photodetectors Operating at 10 μm with a Flat Frequency Response up to 70 GHz at Room Temperature

III–V semiconductor mid-infrared photodetectors based on intersubband transitions hold great potential for ultra-high-speed operation up to several hundreds of GHz. In this work we exploit a ∼350 n...

High Speed Terahertz Devices via Emerging Hybrid GNRFET/Josephson Junction Technologies

An approach to merge superconducting Josephson junction (JJ) devices with nanoscale Graphene devices in order to achieve high gain-bandwidth-product on the order of THz is proposed. While JJ-based devices have existed since nearly 1962, interfacing or interacting with them with standard electrical systems has been a challenge for several reasons, including operating temperature, switching speed, and low-signal sensitivity. In this article, we investigated the possibility of utilizing JJ's so-called ac effect in order to generate high frequency signals that can be accommodated by high speed nanoscale devices. Graphene nanoribbon field effect transistors (GNRFET) have been emphasized for their very high frequency operation that is appropriate to accommodate the very high switching speed of the JJ devices. The article is based on the ac JJ effect with generating a sinusoidal current whose frequency directly scales with voltage. For a single-stage GNRFET CS amplifier, a gain of 35.7 dB with a bandwidth of 217 GHz was achieved, while 10.8 dB with a unitary gain of 2.5 THz was also accomplished. This article details the design and interface of the JJ with GNRFET devices, targeting high frequency signal generation on the order of hundreds of GHz to THz, with the purpose of providing a foundation on top of which further developments can be made, especially in the areas of communications, medical devices, instrumentation and measurement devices, high-speed imaging, subinfrared antenna arrays, and computer architecture and hardware, by providing a system, which can respond to speeds on the order of fifty to one hundred times faster than current commercial computer equipment or signal generation/processing.