Abstract-Prospective Beamforming Technologies for Ultra-Massive MIMO in Terahertz Communications: A Tutorial

 

Boyu Ning, Zhongbao Tian, Zhi Chen, Chong Han, Jinhong Yuan, Shaoqian Li

https://arxiv.org/abs/2107.03032

Terahertz (THz) communications with a frequency band 0.1-10 THz are envisioned as a promising solution to the future high-speed wireless communication. Although with tens of gigahertz available bandwidth, THz signals suffer from severe free-spreading loss and molecular-absorption loss, which limit the wireless transmission distance. To compensate the propagation loss, the ultra-massive multiple-input-multiple-output (UM-MIMO) can be applied to generate a high-gain directional beam by beamforming technologies. In this paper, a tutorial on the beamforming technologies for THz UM-MIMO systems is provided. Specifically, we first present the system model of THz UM-MIMO and identify its channel parameters and architecture types. Then, we illustrate the basic principles of beamforming via UM-MIMO and introduce the schemes of beam training and beamspace MIMO for THz communications. Moreover, the spatial-wideband effect and frequency-wideband effect in the THz beamforming are discussed. The joint beamforming technologies in the intelligent-reflecting-surface (IRS)-assisted THz UM-MIMO systems are introduced. Further, we present the corresponding fabrication techniques and illuminate the emerging applications benefiting from THz beamforming. Open challenges and future research directions on THz UM-MIMO systems are finally highlighted.

Marek’s Take: Terahertz spectrum will pave the way to 6G

 

by Sue Marek

https://www.fiercewireless.com/wireless/marek-s-take-terahertz-spectrum-will-pave-way-to-6g

5G may still be in its infancy, but researchers are already looking ahead to next “G” and a big part of their focus is on Terahertz (THz) spectrum frequencies. It may take some creative engineering, but this spectrum, which is very high on the frequency chart, is thought to be as useful to mobile operators for delivering 6G services as millimeter (mmWave) spectrum is for delivering certain 5G applications.

High on the frequency chart

There are really two components to the THz spectrum band: sub-THz, which is in the range of 100 GHz to 300 GHz, and THz, which is from 300 GHz to 3 THz on the spectrum chart. The sub-THz is also known as D-band spectrum, which falls in the range of 130 GHz to 175 GHz.

The benefits of THz spectrum are that it can deliver data-intensive, high bandwidth applications at super-fast speeds for a short distance.

In March 2019 the FCC saw the potential of the THz bands and issued its Spectrum Horizons Report and Order, which created a new category of experimental licenses for use of frequencies between 95 GHz and 3 THz. These licenses are intended to give researchers the flexibility to conduct experiments lasting up to 10 years, and to more easily market equipment during the experimental period.

Many companies are devoting research and development dollars to exploring THz frequencies. Last summer, Samsung released a white paper detailing its vision for 6G and said that it believes it’s inevitable that the THz spectrum bands will be used in future mobile communications systems.

But Samsung isn’t alone. Apple also is looking for wireless research systems engineers to specifically work on 6G. In a recent advertisement the company said it wanted someone with an understanding of multi-antenna techniques as well as “preferred qualifications” such as familiarity with wireless system design in high frequencies, including GHz and THz.

Mobile or fixed?

According to Andreas Roessler, technology manager at test equipment firm Rhode & Schwarz, a signal can travel in THz spectrum for about 100 to 150 meters. However, similar to mmWave spectrum, that signal may be impacted by environmental conditions, such as heavy rain and snow.

“You can pump a lot of data across a 10 GHz wide channel but your problem is your noise power is so high,” he said, explaining that one way to solve this is to have an antenna array that forms a pencil-thin beam. This helps eliminate interference but it also means that the receiver of that signal must be highly coordinated and be in line of sight, otherwise there may be interference problems. 

Because of this challenge, Roessler is uncertain whether THz spectrum will be used for a mobile wireless service. Instead, he believes THz spectrum might work best for a fixed wireless implementation or backhaul or for a specific application such as location sensing.

But not everyone agrees with this. Ted Rappaport, founding director of NYU Wireless, which is currently conducting 6G research, said that it’s a myth to think that THz frequencies have more issues with interference and attenuation than mmWave spectrum.

Instead, he said that many of the lessons learned from mmWave spectrum will work well for THz spectrum. And he believes that THz frequencies will be used for mobile applications as well as fixed wireless and backhaul. “Mobility will happen,” he said. “Mobility requires more sophistication but we will make it work.”

6G in 2030

Roessler said that it’s likely there will be some form of 6G services available in 2030 but he cautions that there are still a lot of steps that have to be accomplished to get to a place where THz spectrum can be used for wireless communications, regardless of whether it’s fixed or mobile. 

He also thinks that THz frequencies, similar to mmWave, may end up being used in certain regions of the world but not necessarily all across the globe. “It really depends upon the country and the region,” he said. 

And even though mobile operators around the globe are working feverishly to expand their 5G footprints, Rappaport is confident that the 6G standard using THz frequencies will move forward rapidly. He also believes that 2030 is a realistic time frame for 6G services to become a reality.

“It takes a lot of R&D to move to a new standard,” he said. “But it’s too compelling to not do it. When you get that much more bandwidth and 10 times the capacity that means you can bring new capabilities and functionality to consumers.”

Abstract-Terahertz communications at various atmospheric altitudes

Author links open overlay panelAkhtar Saeed, Ozgur Gurbuz, Mustafa Alper,

https://www.sciencedirect.com/science/article/pii/S1874490720301907?dgcid=rss_sd_all

Terahertz communications offers a massive potential for the prospective beyond 5G wireless systems, as the band offers huge bandwidth and data rates as compared to the existing sub 6 GHz bands, which are almost saturated. In this paper, we investigate the feasibility of wireless communications over the Terahertz-band (0.75–10 THz) at various atmospheric altitudes, considering different transmission distances and directions by realistically calculating the absorption loss, which is the major limiting factor affecting the propagation of THz waves through the earth’s atmosphere. Four practical altitudes are considered, corresponding to Drone-to-Drone (D2D), Jet plane-to-Jet plane (J2J), Unmanned Aerial Vehicle (UAV)-to-UAV, and near-space Satellite-to-Satellite (S2S) communications. Following comparison and validation with two real-world experimental results from the literature measured at the sea-level, Line by Line Radiative Transfer Models (LBLRTM) is used to obtain realistic THz-band transmittance values against each altitude case and setting. Subsequently, absorption loss and total path loss values are computed and mean total path loss sensitivity is further observed against a range of transmission directions via zenith angle variations from vertically-up to vertically-down communication. Numerical results show that as the altitude increases, the concentration of the water vapor molecules decreases, enabling the communication over the THz-band (0.75–10 THz) to be more feasible as compared to the sea-level communication. Moreover, the total usable bandwidth results over the THz-band (0.75–10 THz) exhibit that the upper bounds of 8.218 THz, 9.142 THz and 9.25 THz are usable up to the transmission distance of 2 km against the total antenna gains of 80 dBi for J2J, U2U and S2S communication cases, respectively.

Abstract-Spatiotemporal Dielectric Metasurfaces for Unidirectional Propagation and Reconfigurable Steering of Terahertz Beams

Longqing Cong,  Ranjan Singh

https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202001418

Next‐generation devices for low‐latency and seamless communication are envisioned to revolutionize information processing, which would directly impact human lives, technologies, and societies. The ever‐increasing demand for wireless data traffic can be fulfilled by the terahertz band, which has received tremendous attention as the final frontier of the radio spectrum. However, attenuation due to atmospheric humidity and free‐space path loss significantly limits terahertz signal propagation. High‐gain antennas with directional radiation and reconfigurable beam steering are indispensable for loss compensation and terahertz signal processing, which are associated with spatial and temporal dimensions, respectively. Here, experimental demonstration of a spatiotemporal dielectric metasurface for unidirectional propagation and ultrafast spatial beam steering of terahertz waves is shown. The spatial dimension of the metasurface provides a solution to eliminate backscattering of collimated unidirectional propagation of the terahertz wave with steerable directionality. Temporal modulation of the spatial optical properties enables ultrafast reconfigurable beam steering. Silicon‐based spatiotemporal devices amalgamate the rich physics of metasurfaces and technologies that are promising for overcoming the bottlenecks of future terahertz communication, such as high‐speed and secure wireless data transmission, beamforming and ultrafast data processing.

Abstract-Terahertz communications at various atmospheric altitudes

Akhtar Saeed, Ozgur Gurbuz,  Mustafa Alper Akkas,



https://www.sciencedirect.com/science/article/pii/S1874490720301907

Terahertz communications offers a massive potential for the prospective beyond 5G wireless systems, as the band offers huge bandwidth and data rates as compared to the existing sub 6 GHz bands, which are almost saturated. In this paper, we investigate the feasibility of wireless communications over the Terahertz-band (0.75–10 THz) at various atmospheric altitudes, considering different transmission distances and directions by realistically calculating the absorption loss, which is the major limiting factor affecting the propagation of THz waves through the earth’s atmosphere. Four practical altitudes are considered, corresponding to Drone-to-Drone (D2D), Jet plane-to-Jet plane (J2J), Unmanned Aerial Vehicle (UAV)-to-UAV, and near-space Satellite-to-Satellite (S2S) communications. Following comparison and validation with two real-world experimental results from the literature measured at the sea-level, Line by Line Radiative Transfer Models (LBLRTM) is used to obtain realistic THz-band transmittance values against each altitude case and setting. Subsequently, absorption losses and total path loss values are computed and mean total path loss sensitivity is further observed against a range of transmission directions via zenith angle variations from vertically-up to vertically-down communication. Numerical results show that as the altitude increases, the concentration of the water vapor molecules decreases, enabling the communication over the THz-band (0.75–10 THz) to be more feasible as compared to the sea-level communication. Moreover, the total usable bandwidth results over the THz-band (0.75–10 THz) exhibit that the upper bounds of 8.218 THz, 9.142 THz and 9.25 THz are usable up to the transmission distance of 2 km against the total antenna gains of 80 dBi for J2J, U2U and S2S communication cases, respectively.

Novel Materials Could Help Terahertz Chips Deliver Data at Terabits-Per-Second Rates

Photonic topological insulators and terahertz waves could together deliver data at ultra-fast speeds

Image: Nanyang Technological University/Nature Photonics

An artist's representation of the silicon chip. The orange wavy line represents terahertz rays, which travel topologically protected in the interface between the two different sets of triangular holes. On the right, data is encoded into transmitted terahertz rays. On the left, data is received from the terahertz rays in applications involving wireless communication.

By Charles Q. Choi

https://spectrum.ieee.org/nanoclast/computing/hardware/terahertz-chip

Novel materials known as photonic topological insulators could one day help terahertz waves send data across chips at unprecedented speeds of a trillion bits per second, a new study finds. 

Terahertz waves fall between optical waves and microwaves on the electromagnetic spectrum. Ranging in frequency from 0.1 to 10 terahertz, terahertz waves could be key to future 6G wireless networks. With those networks, engineers aim to transmit data at terabits (trillions of bits) per second.

Such data links could also greatly boost intra-chip and inter-chip communication to support artificial intelligence (AI) and cloud-based technologies, such as autonomous driving.

"Artificial intelligence and cloud-based applications require high volumes of data to be transmitted to a connected device with ultra-high-speed and low latency," says Ranjan Singh, a photonics researcher at Nanyang Technological University in Singapore and coauthor of the new work. "Take for example, an autonomous vehicle that uses AI to make decisions. In order to increase the efficiency of decision-making tasks, the AI-sensors need to receive data from neighboring vehicles at ultra-high speed to perform the actions in real time."

Conventional terahertz waveguides are vulnerable to fabrication defects and considerable signal loss at sharp bends. Now, researchers find the burgeoning field of topological photonics may help solve these problems.

Topology is the branch of mathematics that explores what features of shapes can survive deformation. For instance, an object shaped like a doughnut can get pushed and pulled into the shape of a mug, with the doughnut's hole forming the hole in the cup's handle, but it could not get deformed into a shape that lacked a hole without ripping the item apart.

Using insights from topology, researchers developed the first electronic topological insulators in 2007. Electrons traveling along the edges or surfaces of these materials strongly resist any disturbances that might hamper their flow, much as a doughnut might resist any change that would remove its hole.

Recently, scientists have designed photonic topological insulators in which photons of light are similarly "topologically protected." These materials possess regular variations within their structures that lead specific wavelengths of light to flow within them without scattering or losses, even around corners and imperfections.

Image: Nanyang Technological University/Nature Photonics

An optical image of the silicon chip. The white dashed line represents the interface between the two different sets of triangular holes.

Prior work on photonic topological insulators was largely focused on microwave and optical frequencies. Now researchers say they have for the first time experimentally achieved topological protection of terahertz waves.

Scientists fabricated a silicon chip that was 190 microns thick and measuring 8 millimeters by 26 millimeters. They perforated it with rows of triangular holes that alternated in size between 84.9 microns and 157.6 microns, with the smaller triangles pointing the opposite direction of the larger ones. These rows of holes were arranged in clusters where all the larger triangles either pointed up or down. Light entering this chip flowed topologically protected along the interface between the different sets of holes.

Photos: Nanyang Technological University/Nature Photonics

An experimental demonstration of uncompressed 4K high-definition video transmission using the new chip (right). The transmitted 4K high-definition video is shown on the monitor in the background. The terahertz-signal transmitter is on the left side; the receiver is on the right side.

In experiments, the researchers found terahertz waves could also travel smoothly with virtually no losses even when routed around 10 sharp corners, including five 120-degree turns and five 60-degree turns. They achieved data transfer rates of 11 gigabits per second at a frequency of 0.335 terahertz with a bit error rate of less than 1 in 100 billion. They also showed they could transmit uncompressed 4K high-definition video in real-time through their chip across those 10 sharp bends at a rate of 6 gigabits per second.

Previous research achieved data rates of 1.5 gigabits per second with terahertz waves and photonic crystals (structures possessing features smaller than the wavelengths of light they’re designed to deal with). Not only does the photonic topological insulator in the new work display higher data transfer rates, but traditional photonic crystals experience huge signal loss at bends, whereas such losses are negligible in the new material. "This is important when we consider miniaturization of devices in designing on-chip multiplexers and splitters, which normally require bending of waveguides," says Masayuki Fujita, a coauthor and photonics researcher at Osaka University in Japan.

The researchers note there are a number of ways to boost the data rates of their setup to achieve terabit-per-second speeds, though they haven’t yet demonstrated those rates in an experiment. These techniques include using higher frequencies, more bandwidth, and more complex data-encoding schemes.

The scientists detailed their findings on 13 April in the journal Nature Photonics.

Abstract-Increasing Reliability of Terahertz Communication Links Using Onboard Fiber Connectivity

Kathirvel Nallappan, Yang Cao, Guofu Xu, Hichem Guerboukha,  Chahe Nerguizian, Maksim Skorobogatiy

https://ieeexplore.ieee.org/document/9031199

Terahertz (THz) band is the next frontier for the ultra-high-speed communication systems. Currently, most of communications research in this spectral range is focused on wireless systems, while waveguide/fiber-based links have been less explored. Although free space communications have several advantages, the fiber-based communications provide superior performance in certain short-range communication applications. In this work, we study the use of subwavelength dielectric THz fibers for information transmission. Particularly, we use polypropylene-based rod-in-air subwavelength dielectric THz fibers of various diameters (0.57-1.75 mm) to study link performance as a function of the link length of up to ∼10 m, and data bitrates of up to 6 Gbps at the carrier frequency of 128 GHz. Furthermore, we compared the power budget of the rod-in-air subwavelength THz fiber-based links to that of free space communication links and we demonstrate that fiber links offer an excellent solution for various short-range applications.

Abstract-Terahertz Communications (TeraCom): Challenges and Impact on 6G Wireless Systems

Chong Han, Yongzhi Wu, Zhi Chen, Xudong Wang

https://arxiv.org/abs/1912.06040

Terahertz communications are envisioned as a key technology for 6G, which requires 100+ Gbps data rates, 1-millisecond latency, among other performance metrics. As a fundamental wireless infrastructure, the THz communication can boost abundant promising applications, including next-generation WLAN systems like Tera-WiFi, THz wireless backhaul, as well as other long-awaited novel communication paradigms. Serving as a basis of efficient wireless communication and networking design, this paper highlights the key THz channel features and recent advancements in device technologies. In light of these, impact and guidelines on 6G wireless communication and networking are elaborated. We believe the progress of THz technologies is helping finally close the so called THz Gap, and will realize THz communications as a pillar of 6G wireless systems.

Abstract-Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems

Hadeel Elayan, Osama Amin, Basem Shihada, Raed M. Shubair, Mohamed-Slim Alouini

https://arxiv.org/abs/1907.05043

Ultra-high bandwidth, negligible latency and seamless communication for devices and applications are envisioned as major milestones that will revolutionize the way by which societies create, distribute and consume information. The remarkable expansion of wireless data traffic that we are witnessing recently has advocated the investigation of suitable regimes in the radio spectrum to satisfy users' escalating requirements and allow the development and exploitation of both massive capacity and massive connectivity of heterogeneous infrastructures. To this end, the Terahertz (THz) frequency band (0.1-10 THz) has received noticeable attention in the research community as an ideal choice for scenarios involving high-speed transmission. Particularly, with the evolution of technologies and devices, advancements in THz communication is bridging the gap between the millimeter wave (mmW) and optical frequency ranges. Moreover, the IEEE 802.15 suite of standards has been issued to shape regulatory frameworks that will enable innovation and provide a complete solution that crosses between wired and wireless boundaries at 100 Gbps. Nonetheless, despite the expediting progress witnessed in THz wireless research, the THz band is still considered one of the least probed frequency bands. As such, in this work, we present an up-to-date review paper to analyze the fundamental elements and mechanisms associated with the THz system architecture.

Abstract-Design of Terahertz CMOS Integrated Circuits for High-Speed Wireless Communication

Minoru Fujishima, Shuhei Amakawa,

https://digital-library.theiet.org/content/books/cs/pbcs035e

Communications technology at a frequency range into Terahertz (THz) levels has attracted attention because it promises near-fibre-optic-speed wireless links for the 5G and post-5G world. Transmitter and receiver integrated circuits based on CMOS, which has the ability to realize such circuits with low power consumption at a low cost, are expected to become increasingly widespread, with much research into the underlying electronics currently underway. This book describes recent research on terahertz CMOS design for high-speed wireless communication. The topics covered include fundamental technologies for terahertz CMOS design, amplifier design, physical design approaches, transceiver design, and future prospects. This concise source of key information, written by leading experts in the field, is intended for researchers and professional circuit designers working in RFIC and CMOS design for telecommunications.

Abstract-Modulators for Terahertz Communication: The Current State of the Art

Z. T. Ma, Z. X. Geng, Z. Y. Fan3, J. Liu, H. D. Chen

https://spj.sciencemag.org/research/2019/6482975/

With the increase of communication frequency, terahertz (THz) communication technology has been an important research field; particularly the terahertz modulator is becoming one of the core devices in THz communication system. The modulation performance of a THz communication system depends on the characterization of THz modulator. THz modulators based on different principles and materials have been studied and developed. However, they are still on the way to practical application due to low modulation speed, narrow bandwidth, and insufficient modulation depth. Therefore, we review the research progress of THz modulator in recent years and evaluate devices critically and comprehensively. We focus on the working principles such as electric, optical, optoelectrical, thermal, magnetic, programmable metamaterials and nonlinear modulation methods for THz wave with semiconductors, metamaterials, and 2D materials (such as graphene, molybdenum disulfide, and tungsten disulfide). Furthermore, we propose a guiding rule to select appropriate materials and modulation methods for specific applications in THz communication.

Fraunhofer breaks new ground with 4K over THz transmission

FRAUNHOFER HHI AND IAF DEMONSTRATE THE FIRST WIRELESS REAL-TIME VIDEO TRANSMISSION USING TERAHERTZ

http://www.inavateonthenet.net/news/article/fraunhofer-breaks-new-ground-with-4k-over-thz-transmission

The Fraunhofer Heinrich Hertz Institute HHI has announced that 4K video has been sent in real-time over a wireless Terahertz (THz) link for the first time.

Headquartered in Berlin, the institute develops wireless transmission systems claimed to go beyond the capabilities of 5G. THz is said to support “significantly” higher data transmission rates than current 5G mobile wireless technologies. 

Researchers of the department Photonic Networks and Systems, in collaboration with the Fraunhofer Institute for Applied Solid State Physics IAF, succeeded in transmitting a 4K video in real-time over a wireless THz link. A wireless transmission capacity of 100 Gbit/s was demonstrated. 

Dr Robert Elschner, head of internal Terahertz research activities at the Fraunhofer HHI Photonic Networks and Systems department, said: "We were able to achieve stable, continuous operation of the system for more than 70 hours. This is a significant milestone for wireless Terahertz technology." 

The components at the heart of the transmission system are fast, III-V semiconductor-based integrated circuits from Fraunhofer IAF, as well as a high-performance Terahertz modem from Fraunhofer HHI. The transmission used a carrier frequency of 300 GHz across 60cm. 

Dr Colja Schubert, head of the responsible research group "Submarine and Core Systems" at Fraunhofer HHI, said the rate and distance of transmission can be increased further: "It should be possible to realize data rates of 400 Gbit/s and more over short distances. Using optimised antennas, we'll be able to span distances of up to 1 km."

Abstract-Extending Spatial and Temporal Characterization of Indoor Wireless Channels From 350 to 650 GHz

Heng Zhao, Leihao Wei, Mona Jarrahi, Gregory J. Pottie

https://ieeexplore.ieee.org/document/8651537

Communication at terahertz carrier frequencies is a promising way to satisfy the ever-growing demands for high-speed wireless networks. The studies of terahertz wireless channels have so far been limited to the atmospheric transmission bands below 350 GHz. Availability of high-power transmitters and high-sensitivity receivers at higher frequencies necessitates extending the wireless channel studies to enable higher data-rate communication systems. With a view to assessing communication system design requirements at higher frequencies, we present the channel measurement results for 650-GHz carrier frequencies in comparison with 350 GHz carrier frequencies in a typical indoor environment. To obtain the spatial and temporal characteristics of the channel, the power angle profile and the power delay profile are measured based on new measurement methods. Multiple spatially resolvable paths are observed at both 350- and 650-GHz carrier frequencies. Signal-to-noise ratio of the received signal through the non-line-of-sight (NLoS) paths is sufficiently high to enable robust communication when the direct line-of-sight (LoS) path is blocked due to a moving object. The measurement results are used to calculate the reduction in the 650-GHz channel capacity in comparison with that of the 350-GHz channel for both LoS and NLoS paths. Channel dispersion characterization over a 10-GHz bandwidth shows that the delay spreads for the resolved LoS and NLoS paths are less than 80 ps for both 350- and 650-GHz bands. Therefore, no complicated equalizer is required to compensate for channel dispersion at both 350 and 650-GHz, which greatly simplifies the terahertz transceiver design.

Abstract-MAC Protocols for Terahertz Communication: A Comprehensive Survey

Saim Ghafoor, Noureddine Boujnah, Mubashir Husain Rehmani, Alan Davy

https://arxiv.org/abs/1904.11441

Terahertz communication is emerging as a future technology to support Terabits per second link (Tbps) with highlighting features as high throughput and negligible latency. However, the unique features of Terahertz band such as high path loss, scattering and reflection pose new challenges and results in short communication distance. The antenna directionality, in turn, is required to enhance the communication distance and to overcome the high path loss. However, these features in combine negate the use of traditional Medium access protocols. Therefore novel MAC protocol designs are required to fully exploit their potential benefits including efficient channel access, control message exchange, link establishment, mobility management, and line-of-sight blockage mitigation. An in-depth survey of Terahertz MAC protocols is presented in this paper. The paper highlights the key features of the Terahertz band which should be considered while designing an efficient Terahertz MAC protocol, and the decisions which if taken at Terahertz MAC layer can enhance the network performance. Different Terahertz applications at macro and nano scales are highlighted with design requirements for their MAC protocols. The MAC protocol design issues and considerations are highlighted. Further, the existing MAC protocols are also classified based on network topology, channel access mechanisms, and link establishment strategies as Transmitter and Receiver initiated communication. Some open challenges and future research directions on Terahertz MAC protocols are highlighted.

Abstract-Dynamic Photoinduced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures

Yuncheng Zhao, Yaxin Zhang, Qiwu Shi, Shixiong Liang,  Wanxia Huang,  Wei Kou,  Ziqiang Yang,

https://pubs.acs.org/doi/10.1021/acsphotonics.8b00276

Utilizing terahertz (THz) waves to transmit data for communication and imaging places high demands on phase modulation. However, until now, it is difficult to realize a more than 100° phase shift in the transmission mode with one-layer structure. In this paper, a ring-dumbbell composite resonator nested with VO2 nanostructures is proposed to achieve the large phase shift. It is found that in this structure a hybrid mode with an enhanced resonant intensity, which is coupled by the L-C resonance and dipole resonance has been observed. Applying the photoinduced phase transition characteristics of VO2, the resonant intensity of the mode can be dynamically controlled, which leads to a large phase shift in the incident THz wave. The dynamic experimental results show that controlling the power of the external laser can achieve a phase shift of up to 138° near 0.6 THz using this one-layer VO2 nested composite structure. Moreover, within a 55 GHz (575–630 GHz) bandwidth, the phase shift exceeds 130°. This attractive phase shift modulation may provide prospective applications in THz imaging, communications, and so on.

Terahertz spectrum could be new non-line-of-sight optical communications medium

IMAGE: A directional terahertz wireless link (left) bounces off walls, so that there is no line-of-sight path from the transmitter to the receiver. The inset shows the bit error rate (BER) on a log scale, as a function of the output power of the transmitter. At both 100 GHz and 200 GHz, essentially error free transmission (BER = 10exp-9) can be achieved. A close-up photo (right) shows the transmitter rig used in these measurements, which includes a horn antenna and a Teflon lens to increase the gain of the system. (Image credit: Brown University)

by Gail Overton 

https://www.laserfocusworld.com/articles/2018/10/terahertz-spectrum-could-be-new-non-line-of-sight-optical-communications-medium.html

A new range of frequencies in the terahertz (THz) region of the spectrum may soon be available to support the growing communications demand for more bandwidth. A paper in APL Photonics, from AIP Publishing, demonstrates the feasibility of using THz carrier waves for data transmission in diverse situations and environments, including non-line-of-sight applications where waves bounce off, or are reflected by, walls and other objects. 

Daniel Mittleman of Brown University (Providence, RI), whose group led the study, said, "We're not the first group to study the feasibility of THz wireless links, either indoors or outdoors, but there have been few comprehensive studies." Many researchers in the field have believed that links that rely on indirect, or non-line-of-sight pathways, are impossible. "Our work shows that this isn't necessarily the case," he said.

THz radiation has frequencies higher than 95 gigahertz (GHz), beyond which the US Federal Communications Commission (FCC) has yet to establish service rules. Bandwidth in this region of the spectrum could be available for use in future wireless (free space optical or FSO) technologies, but little is known about power requirements, architectures, hardware or other basic issues for such data carrier waves. 

THz radiation is about 100 times higher in frequency and, thus, higher in photon energy than typical wireless carrier waves like Bluetooth or standard Wi-Fi are. Some have expressed concern about the safety of this type of radiation, but because these waves are not likely to penetrate deeply into tissue, particularly at the powers used in wireless applications, most believe safety will not be an issue. 

Mittleman's group measured data transmission at 100, 200, 300 and 400 GHz using a link with a data transfer rate of 1 gigabit per second in a variety of real-life environments. They set up a THz transmitter that used a frequency multiplier chain to up-convert a modulated base signal to the desired frequency. They also placed a receiver downstream, around various indoor and outdoor obstacles, to detect the pulsed signal. Outdoor measurements were enabled by an experimental license granted by the FCC. 

When the THz signal was pointed directly at the receiver, it produced a line-of-sight measurement. Alternatively, the signal could also be forced to reflect from, or bounce off, objects before detection. These non-line-of-sight experiments used real-life objects, including a painted cinder block, a door, metal foil, and a smooth metal plate, to reflect the signal. 

In a key experiment, the signal source and receiver were placed where they could not see each other. The signal was bounced off an intervening wall twice and easily detected by the receiver. This study demonstrated that, contrary to prior expectations, non-line-of-sight use is possible for this type of carrier wave, and that THz radiation may play a role in future wireless technologies

Abstract-Terahertz communication windows and their point-to-point transmission verification

Zhenyang Xiao, Qiujie Yang, Jingguo Huang, Zhiming Huang, Wei Zhou, Yanqing Gao, Rong Shu, and Zhiping He

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-27-7673

Terahertz communication is recognized as a transformational technology that can meet the future demands of point-to-point communication. The study of terahertz atmospheric transmission characteristics is important for guiding the terahertz communication window selection process. In this report, based on the modified ITU-R P.676-10 model, we determined that the terahertz communication windows above 100 GHz were located at the bands at approximately 140, 220, 340, 410, and 460 GHz, which is verified by recent experiments. We also verified the feasibility of indoor point-to-point communication by the 110 m transmission experiment through the communication window around 460 GHz.

© 2018 Optical Society of America

Marconi Society Friend Ted Rappaport: Terahertz – The Next Frontier for Communications & Electronics

http://marconisociety.org/marconi-society-friend-ted-rappaport-terahertz-the-next-frontier-for-communications-electronics/

NYU WIRELESS and the NYU Tandon School of Engineering Organize Series to Spur Research in the Emerging Field

The next frontier for ultra-fast computing and wireless communications – the terahertz electromagnetic spectrum – will be examined in a series of seminars by foremost scientists and engineers in the field. Organized by the NYU WIRELESS research center and NYU Tandon School of Engineering’s Electrical and Computer Engineering Department, the series at the school’s Brooklyn, New York, campus will be streamed for NYU WIRELESS industrial affiliate sponsors and the public and archived for later viewing.

“Circuits: Terahertz (THZ) and Beyond” will explore the vast unknown that lies between the optical spectrum and the millimeter wave (mmWave) frequencies that will soon carry massive amounts of data in 5G, or fifth generation, of cellphone devices. Physicists, mathematicians, and engineers have been working for decades trying to solve fundamental challenges of the THz spectrum and pushing the boundaries of quantum nanoelectronics in the hope of unlocking even more gains for communications, computing, sensing, and materials.

“Recent breakthroughs in THz research, quantum computing, and nanotechnology have opened  exciting new vistas for the future of electrical and computer engineering, and NYU has made major investments in these promising areas already,” said Professor Theodore (Ted) S. Rappaport, director and founder of NYU WIRELESS. “While we have pioneered the use and understanding of mmWave frequencies for 5G, it is clear that new knowledge will be needed to bridge the gap between the fundamentals of these new areas with the design and fabrication of devices. In keeping with the NYU WIRELESS tradition, we also seek to amplify the global conversation in these exciting areas by organizing this series and making it free and open to all.”

“The spectrum also holds great promise for communications and networks – both strongholds of NYU Tandon research – as well as sensing and optics,” said Professor Ivan Selesnick, chair of the department. The THz seminar series reflects our commitment to both educate students and foster the pursuit of new important research areas in electronics and wireless communication.”

“This new series will bring leaders in this emerging field of study to Brooklyn, to the benefit of our students, faculty, and all of New York, as well as scholars worldwide,” said new NYU Tandon Dean Jelena Kovačević, whose academic background is electrical and biomedical engineering. “Our faculty and NYU WIRELESS established Brooklyn as a world-renowned center for mmWave technology, and the excitement is palpable here as they explore technologies that will drive communication and computing decades hence.”

The inaugural seminar, on Wednesday, September 5, 2018, will feature Aydin Babakhani speaking on “Silicon-based Integrated Sensors with On-chip Antennas: From THz Pulse Sources to Miniaturized Spectrometers.” An associate professor of electrical and computer engineering at the UCLA Henry Samueli School of Engineering and Applied Science and director of the Integrated Sensors Laboratory at UCLA, Babakhani’s research could have major implications for biomedical devices. For example, Babakhani designed a wireless, battery-free pacemaker that receives energy through radio frequency radiation and eliminates the need for risky surgeries to replace batteries.

All seminars begin at 11 a.m. Eastern and can be watched at engineering.nyu.edu/live. For more information, including the full schedule of speakers, locations, and the department’s acclaimed series on artificial intelligence, visit https://engineering.nyu.edu/academics/departments/electrical-and-computer-engineering/ece-seminar-series.

“Circuits: THz and Beyond” is organized by NYU Tandon faculty members Shaloo Rakheja, Davood Shahrjerdi, Ramesh Karri, and Ted Rappaport.
NYU Tandon’s Department of Electrical and Computer Engineering has a long tradition of excellence in teaching and research, dating to 1885. The department rose to prominence in the mid-twentieth century for work in microwaves, communications, electrical machinery, and automatic control. Currently, its faculty and NYU WIRELESS are prominent in mmWave technology, massive MIMO, hardware security, networking, signal processing, and the smart grid. Its research activities are organized into five major areas: Communications, Networking and Signal Processing/Machine Learning; Systems, Control and Robotics; Energy Systems, Smart Grids and Power Electronics; Electromagnetics and Analog/RF/Biomedical Circuits; and Computer Engineering and VLSI.