Tens Of GHz Research Articles

Investigations on Millimeter-Wave Indoor Channel Simulations for 5G Networks

Due to the extensively accessible bandwidth of many tens of GHz, millimeter-wave (mmWave) and sub-terahertz (THz) frequencies are anticipated to play a significant role in 5G and 6G wireless networks and beyond. This paper presents investigations on mmWave bands within the indoor environment based on extensive simulations; the study considers the behavior of the omnidirectional and directional propagation characteristics, including path loss exponents (PLE) delay spread (DS), the number of clusters, and the number of rays per cluster at different frequencies (28 GHz, 39 GHz, 60 GHz and 73 GHz) in both line-of-sight (LOS) and non-LOS (NLOS) propagation scenarios. This study finds that the PLE and DS show dependency on frequency; it was also found that, in NLOS scenarios, the number of clusters follows a Poisson distribution, while, in LOS, it follows a decaying exponential distribution. This study enhances understanding of the indoor channel behavior at different frequency bands within the same environment, as many research papers focus on single or two bands; this paper considers four frequency bands. The simulation is important as it provides insights into omnidirectional channel behavior at different frequencies, essential for indoor channel planning.

Atacama Large Aperture Submillimeter Telescope (AtLAST) science: Planetary and cometary atmospheres.

The study of planets and small bodies within our Solar System is fundamental for understanding the formation and evolution of the Earth and other planets. Compositional and meteorological studies of the giant planets provide a foundation for understanding the nature of the most commonly observed exoplanets, while spectroscopic observations of the atmospheres of terrestrial planets, moons, and comets provide insights into the past and present-day habitability of planetary environments, and the availability of the chemical ingredients for life. While prior and existing (sub)millimeter observations have led to major advances in these areas, progress is hindered by limitations in the dynamic range, spatial and temporal coverage, as well as sensitivity of existing telescopes and interferometers. Here, we summarize some of the key planetary science use cases that factor into the design of the Atacama Large Aperture Submillimeter Telescope (AtLAST), a proposed 50-m class single dish facility: (1) to more fully characterize planetary wind fields and atmospheric thermal structures, (2) to measure the compositions of icy moon atmospheres and plumes, (3) to obtain detections of new, astrobiologically relevant gases and perform isotopic surveys of comets, and (4) to perform synergistic, temporally-resolved measurements in support of dedicated interplanetary space missions. The improved spatial coverage (several arcminutes), resolution (~ 1.2'' - 12''), bandwidth (several tens of GHz), dynamic range (~ 10 5) and sensitivity (~ 1 mK km s -1) required by these science cases would enable new insights into the chemistry and physics of planetary environments, the origins of prebiotic molecules and the habitability of planetary systems in general.

Exciting High‐Frequency Short‐Wavelength Spin Waves using High Harmonics of a Magnonic Cavity Mode

AbstractSpin waves (SWs) are promising objects for signal processing and future quantum technologies due to their high microwave frequencies with corresponding nanoscale wavelengths. However, the nano‐wavelength SWs generated so far are limited to low frequencies. In the paper, using micromagnetic simulations, it is shown that a microwave‐pumped SW mode confined to the cavity of a thin film magnonic crystal (MC) can be used to generate waves at tens of GHz and wavelengths well below 50 nm. These multi‐frequency harmonics of the fundamental cavity mode are generated when the amplitude of the pumping microwave field exceeds a threshold, and their intensities then scale linearly with the field intensity. The frequency of the cavity mode is equal to the ferromagnetic resonance frequency of the planar ferromagnetic film, which overlaps with the magnonic bandgap, providing an efficient mechanism for confinement and magnetic field tunability. The effect reaches saturation when the microstrip feed line covers the entire cavity, making the system feasible for realization.

Fiber-optic spectrum monitoring of wavelength-division-multiplexed telecommunication signals with MHz update rates.

We propose a novel (to our knowledge) and simple real-time optical monitoring (RTOM) system for dynamic spectral analysis of telecommunication signals, involving electro-optic (EO) temporal sampling followed by dispersion-induced frequency-to-time mapping and high-speed photodetection. This system enables tracking of the presence and relative intensity of multiple wavelength-division-multiplexed (WDM) data streams that span over a broad frequency band with high resolution, accuracy, and fast measurement update rates. We derive the design conditions and trade-offs of the proposed scheme and report proof-of-concept experiments and a numerical result that demonstrate successful spectral monitoring of dense-WDM signals with different modulation formats and bit rates, over the full C-band, with the needed resolution to discern channels separated by a few tens of GHz, and with an unprecedented fast measurement update rate in the MHz range.

The wireless communications systems in subterahertz frequency range

Background. The subterahertz and terahertz frequency ranges are very promising for development of high speed wireless communications systems because of possibility to get the bandwidth about some tens of GHz, which provides the high channel capacity. However fast signal attenuation at its propagation in atmosphere complicate the operation of communications systems in these ranges.
 Aim. Use of fixed narrow-beam antennas with high antenna power gain allows to provide the direct surface communications distance to some kilometers. The communications distance limitation can be partially removed decreasing the frequency down to 200 GHz and narrowing the channel bandwidth down to some GHz.
 Methods.The model of transmitter-receiver system (200-220 GHz) based of modern semiconductor devices is described in the manuscript. Results. The possibility of digital signals transmission with speed up to 1 Gbit/s at the distance of 1 km is experimentally shown.
 Conclusion. According to calculations the output power of transmitter about some hundreds mW is enough for data transmission at the distance up to 1.5 km with antenna power gain of no less than 50 dB.

Ultra-narrow inhomogeneous spectral distribution of telecom-wavelength vanadium centres in isotopically-enriched silicon carbide

Spin-active quantum emitters have emerged as a leading platform for quantum technologies. However, one of their major limitations is the large spread in optical emission frequencies, which typically extends over tens of GHz. Here, we investigate single V4+ vanadium centres in 4H-SiC, which feature telecom-wavelength emission and a coherent S = 1/2 spin state. We perform spectroscopy on single emitters and report the observation of spin-dependent optical transitions, a key requirement for spin-photon interfaces. By engineering the isotopic composition of the SiC matrix, we reduce the inhomogeneous spectral distribution of different emitters down to 100 MHz, significantly smaller than any other single quantum emitter. Additionally, we tailor the dopant concentration to stabilise the telecom-wavelength V4+ charge state, thereby extending its lifetime by at least two orders of magnitude. These results bolster the prospects for single V emitters in SiC as material nodes in scalable telecom quantum networks.

Quantitative Ultrafast Magnetoacoustics at Magnetic Metasurfaces.

Femtosecond (fs) time-resolved magneto-optics is applied to investigate laser-excited ultrafast dynamics of one-dimensional nickel gratings on fused silica and silicon substrates for a wide range of periodicities Λ = 400-1500 nm. Multiple surface acoustic modes with frequencies up to a few tens of GHz are generated. Nanoscale acoustic wavelengths Λ/n have been identified as nth-spatial harmonics of Rayleigh surface acoustic wave (SAW) and surface skimming longitudinal wave (SSLW), with acoustic frequencies and lifetimes being in agreement with theoretical calculations. Resonant magnetoelastic excitation of the ferromagnetic resonance (FMR) by SAW's third spatial harmonic, and, most interestingly fingerprints of the parametric resonance at 1/2 SAW frequency have been observed. Numerical solutions of Landau-Lifshitz-Gilbert (LLG) equation magnetoelastically driven by complex polychromatic acoustic fields quantitatively reproduce all resonances at once. Thus, our results provide a solid experimental and theoretical base for a quantitative understanding of ultrafast fs-laser-driven magnetoacoustics and tailoring the magnetic-grating-based metasurfaces at the nanoscale.

Optical generation and detection of GHz longitudinal and transverse acoustic waves in solids assisted by two-dimensional metallic grating structure

Absorption of laser pulses with picosecond temporal width in a two-dimensional nano-scale metallic grating deposited on a transparent substrate launches both longitudinal and transverse acoustic waves in to the sample. The periodic metallic structure makes the generated acoustic waves propagate several different directions. The propagating acoustic waves are monitored optically by the delayed light pulses (probe light) as the transient reflectivity change which is known as the Brillouin oscillation. The probe light is also diffracted by the metallic grating, allowing the detection of the acoustic waves propagating in the multiple directions efficiently. The analysis of the Brillouin oscillation frequencies brings the longitudinal and transverse sound velocities and the optical refractive index simultaneously from a single measurement. We verify the above mentioned scheme using a sample with two-dimensional square lattice (period 380 nm) of aluminum square islands of lateral dimension 200 × 200 nm2 and thickness of 50 nm on a fused silica substrate of thickness 1 mm. From the obtained Brillouin oscillation frequencies in several tens GHz, the acoustic and optical properties of the substrate material are successfully retrieved. The technique would be applicable to investigate the acoustic and optical properties of more complicated systems, such as anisotropic and/or inhomogeneous medium.

Optical Time-Mapped Spectrograms (II): Fractional Talbot Designs

Real-time implementations of joint time-frequency analysis over instantaneous bandwidths above the GHz range remain challenging. In a companion paper, we have proposed an analog photonic processing scheme that enables computing a short-time Fourier transform (STFT), or spectrogram (SP), of an incoming arbitrary broadband signal, over tens-of-GHz analysis bandwidths, in a continuous, gapless and real-time manner. The proposed method involves a temporal sampling of the signal under test (SUT) with a periodic train of interfering, linearly chirped optical pulses followed by group-velocity dispersion to map the spectra of consecutive and overlapping truncated sections of the SUT along the time domain. This scheme offers a notable design versatility to customize the performance specifications of the computed SP, but it generally involves a sub-optimal non-uniform sampling of the SUT and it requires the use of a bulky and expensive pulsed optical source. In this communication, we show that this previous general scheme can be easily configured to ensure an optimal, uniform sampling of the SUT by simply setting the involved dispersive lines to satisfy a fractional self-imaging condition, while keeping all the advantages (e.g., design versatility) of the original scheme. Moreover, the resulting design is further adapted to entirely avoid the need for a pulsed source, using instead a more efficient and simpler phase-only temporal sampling of the SUT, e.g., implemented through electro-optic phase modulation. We derive the design conditions and performance trade-offs of the proposed time-mapped STFT schemes based on dispersion-induced fractional Talbot self-imaging. Through numerical simulations and experimental demonstration, we confirm the potential of this simple and efficient approach for real-time SP analysis of arbitrary signals over instantaneous bandwidths above a few tens of GHz, with MHz frequency resolutions and ultrahigh processing speeds, approaching billions of FTs per second.

Superconducting-Oscillatory Neural Network With Pixel Error Detection for Image Recognition

Brain-inspired oscillatory neural networks (ONNs) utilize coupled oscillators to emulate biological neuronal dynamics. ONNs are naturally suitable for image/pattern recognition. Many hardware implementations of ONNs have been explored recently by using analog or digital CMOS systems, which can be limited by Moore's law. In this work, we used one of the advanced superconducting technologies for coupled oscillator networks to further improve the energy efficiency and processing speed. Inductively coupled ring oscillators using rapid single flux quantum (RSFQ) technology were designed and simulated. These Josephson junction (JJ) based oscillators can operate as fast as tens of GHz but only consume a energy of several aJ per operation. Excluding cryo-cooling factors, the estimated power consumption of our RSFQ oscillator is hundreds of nW at a frequency of 12.5 GHz, which is multiple times smaller than a typical CMOS ring oscillator. Furthermore, a system for pattern recognition with error detection was designed based on these oscillators. Synchronization dynamics in a pair of coupled oscillators were used to identify whether a test pixel matches a reference pixel. A network comprised of 16 pairs of oscillators were wired together, along with synchronization detectors and a fluxon integrator to demonstrate pattern recognition function. This work was performed using standard JJ models and demonstrated through WRspice and JoSIM software simulations. The circuits and systems proposed in this work aim to provide insights into the use of superconducting technology for implementing ONNs and may serve as basic building blocks for the design of more complex oscillatory computational networks in image processing and beyond. Single oscillator modeling and systematic network function exploration will be performed in future work.

Optical Time-Mapped Spectrograms (I): From the Time-Lens Fourier Transformer to the Talbot-Based Design

The short-time Fourier transform (STFT), or spectrogram (SP), is the prime method for joint time-frequency signal analysis and processing. Real-time implementation of this powerful tool over instantaneous bandwidths above the GHz range remains challenging. We propose here a universal analog optical processing approach to obtain the STFT of a high-speed temporal waveform (typically, a microwave signal) in a continuous and real-time manner, and with no gaps in the signal acquisition and analysis. The proposed method is based on a photonics time-mapped Fourier transformer, involving temporal modulation of the signal under test (SUT) with a chirped optical pulse (i.e., a time lens) followed by group-velocity dispersion, in which consecutive, overlapping chirped pulses (or time lenses) are utilized for realization of a continuous and gap-free STFT analysis. We derive the design conditions and performance trade-offs of this general scheme, especially concerning its instantaneous bandwidth, time-frequency resolutions and processing speed (number of FTs per second). Moreover, we also show that a previous, simpler time-mapped STFT design based on Talbot effects, in which the SUT is directly sampled with unchirped pulses before dispersion, can be interpreted and evaluated as a particular case of the time-lens STFT scheme introduced here. This suggests a way of implementing an array of overlapping time lenses by simply sampling the SUT with a suitable periodic train of short pulses. The time-lens STFT scheme offers a remarkable versatility to tailor the specifications of the obtained SP, whereas the Talbot design is particularly interesting for SP analysis with enhanced time resolution and ultrahigh processing speed. Our findings are validated through numerical simulations. The proposed method would enable performing the STFT of signals over instantaneous bandwidths above a few tens of GHz, with MHz frequency resolutions and processing speeds exceeding hundreds of millions of FTs per second using realistic fiber-optics technologies.

Application of magnetically induced [formula omitted] atomic transitions of cesium atoms in strong magnetic fields

In this work, magnetically induced (MI) transitions of the Cs atoms in strong magnetic fields up to 6 kG, and their applications in spectroscopy are studied experimentally and theoretically. An attractive feature of these transitions is their large frequency shift slope in a magnetic field (−4 MHz/G). Therefore, in strong magnetic fields the frequency shift of MI transitions reaches several tens of GHz and importantly, these transitions do not overlap with others, which is of practical interest for possible use in new frequency ranges. To implement the process of electromagnetically induced transparency (EIT) in a strong magnetic field (1–2 kG), the MI Fg=4→Fe=2 transitions were first used at the frequency of probe radiation, while the frequency of coupling radiation is resonant the Fg=3→Fe=2 transitions. To form the EIT resonance, a cell of sub-micron thickness filled with Cs atom vapors was used, along with strong permanent magnets.

Modelling of an intersubband quantum confined Stark effect in Ge quantum wells for mid-infrared photonics.

In this work we theoretically investigate quantum confined Stark effect of intersubband transitions in asymmetric Ge/SiGe quantum wells for intensity modulation in the mid-infrared. Our calculations show that extinction ratios up to 1 dB and modulation speeds of several tens of GHz could be obtained in 100 µm long waveguides.

Spin-defect qubits in two-dimensional transition metal dichalcogenides operating at telecom wavelengths

Solid state quantum defects are promising candidates for scalable quantum information systems which can be seamlessly integrated with the conventional semiconductor electronic devices within the 3D monolithically integrated hybrid classical-quantum devices. Diamond nitrogen-vacancy (NV) center defects are the representative examples, but the controlled positioning of an NV center within bulk diamond is an outstanding challenge. Furthermore, quantum defect properties may not be easily tuned for bulk crystalline quantum defects. In comparison, 2D semiconductors, such as transition metal dichalcogenides (TMDs), are promising solid platform to host a quantum defect with tunable properties and a possibility of position control. Here, we computationally discover a promising defect family for spin qubit realization in 2D TMDs. The defects consist of transition metal atoms substituted at chalcogen sites with desirable spin-triplet ground state, zero-field splitting in the tens of GHz, and strong zero-phonon coupling to optical transitions in the highly desirable telecom band.

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.

Photonic-Assisted Arbitrary Waveform Generation for Uplink Applications in Beyond 5G Taking Advantage of Low Frequency Technology

We present a photonic-assisted arbitrary waveform generation for uplink applications in beyond 5G taking advantage of low frequency technology and it has a potential to upgrade signal frequency from MHz to more than tens GHz retaining the high ENOB of conventional low frequency electrical technology competitive to the state of the arts of tens GHz class AWG. In machine-to-machine communications over uplink traffic as one of application scenario examples, massive multi-data should be accommodated and be conveyed to beyond GHz region in the era of beyond 5G. The proposed photonic assistance for temporal waveform compression has a potential to upgrade signal frequency from MHz to more than tens GHz retaining the high ENOB of the low frequency technology and surpass the state of the arts of tens GHz class AWG. We successfully demonstrate the principle of the proposed approach in experiment and the potential of achievable ENOB over 12 bit at 50 GHz in simulation.

Superconducting Sub-Terahertz Oscillator with Continuous Frequency Tuning

The development and approbation of a superconducting local oscillator based on a long Josephson junction made it possible to create a fully superconducting integrated receiver in sub-terahertz frequency range, which was successfully tested both on board a high-altitude balloon and in the laboratory. In order to expand the frequency range of a superconducting integrated local oscillator, it is necessary to ensure the continuous tuning of its frequency at an arbitrary bias current, including a so-called resonant mode regime. The resonant mode regime takes place for high-quality tunnel junctions with low leakage; in this regime, stable generation is possible only at Fiske steps, the distance in frequency between which is tens of GHz. A method for suppressing resonances has been proposed and implemented; this method is based on the introduction of normal metal layers into the region near the long Josephson junction. Modeling of the propagation of electromagnetic waves in the proposed integrated structure was carried out; experimental samples were fabricated, and their comprehensive study was performed. The complete suppression of resonances and the possibility of the continuous tuning of the frequency of a superconducting local oscillator in the range of 200–700 GHz have been demonstrated. The linewidth of the FFO radiation does not exceed 15 MHz over the entire frequency range, which makes it possible to implement the phase locked loop mode in an integrated receiver intended for spectral studies.

A new LFSR based high-frequency test method for RSFQ circuit

Rapid single flux quantum (RSFQ) circuits have the advantages of high speed and low power consumption. The typical frequency of the RSFQ circuits is tens of GHz. Therefore, it is necessary to reliably test the high-frequency performance of RSFQ circuits simply and effectively. This paper proposes a new on-chip high-frequency testing method, which uses pseudo-random sequences generated by linear feedback shift register (LFSR) as the test vectors, and the output shift registers (SRs) to store the last piece of high-frequency testing result and read out it at low-frequency. Unlike the traditional high-frequency demonstration method of using the Input/Output SRs, our testing system can automatically generate a large number of test vectors to test the circuit at high frequency at low cost, making the whole high-frequency demonstration more reliable and convincing. On the other hand, this method is also a feasible and straightforward on-chip high-frequency test method for various RSFQ circuits. This work verified the proposed method, and the highest test frequency can reach 54 GHz while the circuit shows good operating margins.

The C-Band All-Sky Survey (C-BASS): template fitting of diffuse galactic microwave emission in the northern sky

ABSTRACTThe C-Band All-Sky Survey (C-BASS) has observed the Galaxy at 4.76 GHz with an angular resolution of 0${_{.}^{\circ}}$73 full-width half-maximum, and detected Galactic synchrotron emission with high signal-to-noise ratio over the entire northern sky (δ > −15○). We present the results of a spatial correlation analysis of Galactic foregrounds at mid-to-high (b > 10○) Galactic latitudes using a preliminary version of the C-BASS intensity map. We jointly fit for synchrotron, dust, and free–free components between 20 and 1000 GHz and look for differences in the Galactic synchrotron spectrum, and the emissivity of anomalous microwave emission (AME) when using either the C-BASS map or the 408-MHz all-sky map to trace synchrotron emission. We find marginal evidence for a steepening (<Δβ> = −0.06 ± 0.02) of the Galactic synchrotron spectrum at high frequencies resulting in a mean spectral index of <β> = −3.10 ± 0.02 over 4.76–22.8 GHz. Further, we find that the synchrotron emission can be well modelled by a single power law up to a few tens of GHz. Due to this, we find that the AME emissivity is not sensitive to changing the synchrotron tracer from the 408-MHz map to the 4.76-GHz map. We interpret this as strong evidence for the origin of AME being spinning dust emission.

Fundamental mode transmission around 1310-nm over OM1 and OM2 multimode fibers enabled by a universal fiber modal adapter

Recently there has been an interest in upgrading legacy multimode fibers such as 50 μm OM2 fiber to higher data rates through single mode transmission. A fiber modal adapter hosting a modal conditioning single-mode fiber (MCSMF) has been demonstrated as one robust solution to convert OM2 links into single mode transmission links for higher data rate transmission. Legacy multimode fibers also include OM1 fiber which has higher index contrast between the core and cladding and a larger core of 62.5 μm diameter. In this paper, we conduct a study to understand the MCSMF mode field diameter and connector offset tolerance requirements for OM1 fiber, which affect the transmission performance of single mode transmission. We find that despite very different refractive index profiles between OM1 and OM2 fibers, the fiber modal adapter concept is still applicable to OM1 and only one modal conditioning single-mode fiber design is needed to accommodate the needs for both fiber types. The detailed tolerances to the mode field diameter mismatch and the connector offset are numerically studied. The transfer functions for 1000-m of OM1 and OM2 with the adapters are measured, which show very high modal bandwidths at tens of GHz in contrast to very low modal bandwidths without the adapters. Transmission at 25 Gb/s using a 25G LR transceiver, 100 Gb/s using a 100G CWDM transceiver, and 400 Gb/s using a 400G LR transceiver are demonstrated with error free performance and open eye diagrams over 1000-m of OM1 and OM2. We find that the approach of using MCSMF can support fundamental mode transmission up to 100 Gb/s over this distance without obvious limitations.