Abstract-Tunable metamaterial filter for optical communication in the terahertz frequency range

Wei Yang and Yu-Sheng Lin

Schematic drawing of metamaterial-based TTF. (a) 3D illustration of metamaterial-based TTF. (b) Top-view and (c) 3D illustrations of TTF unit cell and the geometrical parameters. The outer radius (R) is 4.19 µm. The inner radius (r) is 3.89 µm. The line width of the structure (w) is 300 nm. The gap between the ring-shaped and cross-shaped structures (g) is 300 nm. The thickness of metamaterial-based TTF (d) is 300 nm. The height between the bottom ring-shaped and the top cross-shaped structures (h) is variable. (d) Schematic drawing of the proposed TTF for indoor THz wireless communication system application. (e) Fabrication process flow of proposed TTF along AA’ line in (a). (i) The deposition of Au thin-film with 300 nm in thickness for the bottom ring-shaped nanostructure of TTF by using the lift-off process. (ii) The deposition of SiO2 and Si3N4 thin-films by using PECVD sequentially. (iii) The deposition of Au thin-film with 300 nm in thickness for the top cross-shaped nanostructure of TTF by using the lift-off process. (iv) Si3N4 thin-film is patterned by using RIE processes. (v) The microstructures are released by using vapor HF.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-12-17620

We present a design of a tunable terahertz (THz) filter (TTF) used in an indoor communication system. The unit cell of TTF is composed of ring-shaped and cross-shaped nanostructures. By utilizing the micro-electro-mechanical system (MEMS) technique to modify the height between the ring-shaped and cross-shaped nanostructures in the incident transverse electric (TE) mode, the resonant frequencies can be tuned from 0.530 THz to 0.760 THz, which covers an atmospheric window from 0.625 THz to 0.725 THz for indoor wireless optical communication applications. This design of TTF provides an effective approach to select and filter specific signals. It makes the data processing more flexible at the transmission end of the communication system. Furthermore, such a TTF design can be realized the commercialization of communication system components due to its integrated circuit (IC) process compatibility, miniaturization and high flexibility.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Analogue switches made from boron nitride monolayers for application in 5G and terahertz communication systems

Myungsoo Kim, Emiliano Pallecchi, Ruijing Ge, Xiaohan Wu, Guillaume Ducournau, Jack C. Lee, Henri Happy,  Deji Akinwande

Device structure and material characterization.

https://www.nature.com/articles/s41928-020-0416-x

Hexagonal boron nitride (hBN) has a large bandgap, high phonon energies and an atomically smooth surface absent of dangling bonds. As a result, it has been widely used as a dielectric to investigate electron physics in two-dimensional heterostructures and as a dielectric in the fabrication of two-dimensional transistors and optoelectronic devices. Here we show that hBN can be used to create analogue switches for applications in communication systems across radio, 5G and terahertz frequencies. Our approach relies on the non-volatile resistive switching capabilities of atomically thin hBN. The switches are composed of monolayer hBN sandwiched between two gold electrodes and exhibit a cutoff-frequency figure of merit of around 129 THz with a low insertion loss (≤0.5 dB) and high isolation (≥10 dB) from 0.1 to 200 GHz, as well as a high power handling (around 20 dBm) and nanosecond switching speeds, metrics that are superior to those of existing solid-state switches. Furthermore, the switches are 50 times more efficient than other non-volatile switches in terms of a d.c. energy-consumption metric, which is an important consideration for ubiquitous mobile systems. We also illustrate the potential of the hBN switches in a communication system with an 8.5 Gbit s–1 data transmission rate at 100 GHz with a low bit error rate under 10−10.

Abstract-Terahertz Sensing with Optimized Q /V eff Metasurface Cavities

Manoj Gupta,   Ranjan Singh

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201902025

Confinement of electromagnetic radiation in a subwavelength cavity is an important platform for strong light–matter interaction as it enables efficient design of photonic switches, modulators, and ultrasensitive sensors. Metallic metasurfaces consist of an array of planar cavities that allow easy access to confined electromagnetic modes on the surface. However, the radiative and nonradiative losses limit the quality factor (Q ) of the resonantly confined mode. Therefore, metasurface designs with effectively low mode volume (V eff) cavities become extremely important for enhancing the photonic density of states. Here, a symmetric Lorentzian resonant metasurface with lower V eff is demonstrated as compared to asymmetric Fano resonators. Lower mode volume and optimized Q /V eff metasurfaces reveal enhanced sensitivity for ultrathin analyte overlayers deposited on metasurfaces signaling enhanced light–matter interaction. Such metasurfaces with tightly confined electromagnetic modes could find wide range of applications in the development of terahertz metadevices including ultrasensitive sensors, bandpass filters, and energy‐efficient modulators.

Abstract-Room temperature amplification of terahertz radiation by grating-gate graphene structures

Stephane Boubanga-Tombet, Wojciech Knap, Deepika Yadav, Akira Satou, Dmytro B. But, Vyacheslav V. Popov, Ilya V. Gorbenko, Valentin Kachorovskii, and Taiichi Otsuji

https://journals.aps.org/prx/accepted/52079K1dC0014a02342729a68f281fe27fbfc8908

We study terahertz (THz) radiation transmission through grating-gate graphene based nanostructures. We report on room temperature THz radiation amplification stimulated by current-driven plasmon excitation. Specifically, with increase of the dc current under periodic charge density modulation, we observe a strong red shift of the resonant THz plasmon absorption, followed by a window of complete transparency to incoming radiation, and subsequent amplification and blue shift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. Additionally, we present a simple model offering phenomenological description of the observed THz amplification. This model shows that in the presence of dc current the radiation-induced correction to dissipation is sensitive to the phase shift between oscillations of carrier density and drift velocity. And with increasing current, the dissipation becomes negative, leading to amplification. The experimental results of this work, as all obtained at room temperature, pave the way towards the new 2D plasmons based, voltage tuneable THz radiation amplifiers.

Abstract-Controllable terahertz cross-shaped three-dimensional graphene intrinsically chiral metastructure and its biosensing application

Author links open overlay panelSomayyeh Asgari, Nosrat Granpayeh, Tapio Fabritius

https://www.sciencedirect.com/science/article/abs/pii/S0030401820304971

In this research, a three-dimensional (3D) graphene intrinsically chiral metastructure in terahertz (THz) region was proposed and analyzed. The unit cell consists of bi-layer cross-shaped graphene ribbons in which the back layer is rotated compared to the front layer. Parameter retrieval method and Kramers-Kronig relations are used for theoretical analysis and derivation of the right-handed and left-handed electromagnetic effective refractive indices of the proposed structure. Based on our analysis, the proposed meta-structure has a tunable and controllable chiral response due to the tunability of graphene and circular dichroism (CD) was reached to 0.2. In order to evaluate the performance of the THz device in biosensor application, its characteristics in chiral biomolecule (collagen) sensing was analyzed. With an optimum design, our simulations show that the refractive index sensitivity value can be obtained as high as 0.96 THz per refractive index unit (THz/RIU) for the CD spectra. Proposed graphene chiral metastructure is promising enabler for controllable polarization-sensitive devices and systems such as tunable polarization filters, rotators, polarizers, biosensors, phase shifters, operating in the THz region.

Abstract-Survey of terahertz photonics and biophotonics

Kiarash Ahi, Nathan Jessurun, Mohammad-Parsa Hosseini, Navid Asadizanjani

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-59/issue-6/061629/Survey-of-terahertz-photonics-and-biophotonics/10.1117/1.OE.59.6.061629.short?SSO=1

We review the advances of terahertz (THz) science and technology in biophotonics, including related challenges and solutions. The main impediment to THz spectroscopy and imaging in this field is the high absorption of the THz beam in water. Hence, transmission imaging and spectroscopy of thick wet tissue using THz radiation has generally been quite difficult. However, the absorption of THz waves by water molecules is so strong that increasing the power of the THz source can lead to structural and functional changes in tissues, so solutions must go beyond a larger power output. In terms of resolution, THz imaging is superior to ultrasound but inferior to visible light microscopy. Owing to its unique material analysis capabilities, promising diagnosis applications have been demonstrated through THz imaging and spectroscopy. Unfortunately, many applications are limited by beam penetration depth and resolution. Hence, researchers from a wide variety of scientific and technical fields have been actively improving these features through the development of electronic devices and materials. In addition, groundbreaking optical architecture and materials to reduce beam absorption in the optics of a system and generate focused beams with smaller diameters have been proposed. On the software side, image processing techniques to computationally enhance the resolution and quality of THz imaging have been proposed. Data science and machine learning to automate the diagnosis of defects and diseases through processing THz images and spectroscopy data have been proposed. We have reviewed the applications of THz radiation in biophotonics and research achievements toward advancing these applications. A conclusion with a roadmap toward increasing the footprint of the THz technology in biophotonics is also proposed.

© 2020 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2020/$28.00 © 2020 SPIE

Abstract-Toroidal dipole bound states in the continuum metasurfaces for terahertz nanofilm sensing

Xu Chen, Wenhui Fan, and Hui Yan

 (a) Schematic view of the proposed THz metasurface sensor, where THz waves are normal incidence with E-field along x-direction and the analyte is ultrathin nanofilm. (b) Top view of the unit cell with structure parameters are P = 64 µm, L = 50 µm, w = 4 µm, g1 = 3 µm, g2 = 3 µm, d = 4 µm, and δ = 13 µm.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-11-17102

A novel terahertz nanofilm sensor consisting of toroidal dipole bound states in the continuum (TD-BIC) inspired Fano resonance metasurface is proposed and investigated, which exhibits both the TD character and BIC feature. When the mirror symmetry of the unit cell was broken, the TD resonance was excited and demonstrated by anti-aligned magnetic dipoles and calculated scattering powers and the BIC mode was verified with the quality factor satisfying the inverse square law. Combined with the amplitude difference referencing technique, the TD-BIC inspired Fano resonance was utilized for nanofilm sensing at THz frequencies for the first time. Simulation results show that the amplitude difference can be easily observed by comparing the resonance frequency shift under difference thicknesses of germanium overlayer. Moreover, by coating with a 40 nm-thick analyte overlayer, the sensitivity of amplitude difference can achieve 0.32/RIU, which is a significant value and more suitable for sensing nanofilm analytes than the traditional frequency shift method. These advantages make our proposed structure have potential applications in sensing nanofilm analytes.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

OT- LUNA Blog-Structural Health Monitoring is Critical for Dams as America’s Infrastructure Continues to Age

https://lunainc.com/dam-shm-midland/

The collapse of two dams in Midland County, Michigan, has created catastrophic flooding and devastation to communities along the Tittabawassee River. The Edenville Dam, constructed in 1924 and breached Tuesday, was on the Federal Energy Regulatory Commission’s list of high hazard dams, and the previous owners were warned about safety issues. Its collapse lead to flood waters rushing into Sanford Lake, causing the failure of the Sanford Dam, flooding the city of Midland and creating worry that an EPA Superfund site related to excess dioxins could be impacted.

For decades, experts have been warning that aging infrastructure will cause these types of disasters. In its latest Infrastructure Report Card, the American Society of Civil Engineers, found that the average dams in America is 56 years and gave Dams a D Grade. In addition, the report said that 17 percent of dams are considered high-hazard potential.

From older structures to builds in progress, real-time, active monitoring of environmental conditions and structural health is critical to the long-term safety and operation of dams, which distinct features and safety needs depending on the locations where they are built.

High-speed distributed fiber optic sensing delivers fast, accurate and dependable structural health measurements by employing multiple optical measurement technologies using a single instrument. Luna’s rugged fiber optic sensing systems provide continuous, enduring, reliable and accurate measurements of hundreds of optical strain, temperature, acceleration and displacement sensors.

A Luna Innovations structural health monitoring installation of fiber optic sensors and interrogators helps to monitor the Lake Rockwell Spillway around the clock for cracks and bowing of the walls. Covering more than 800 acres, Lake Rockwell is one of the three reservoirs that supplies over 300,000 people in Akron, Ohio with drinking water.

The monitoring system instrumentation is composed of optical interrogators, long-gage strain sensors to better measure strain over the large area between buttresses, accelerometers, temperature sensors, and tilt meters for other crucial measurements. The system continuously monitors the integrity and behavior of the spillway for possible failure or other possible damage.

Luna Innovations has decades of experience helping communities and operators with structural health monitoring on new projects,  like the HZMB Bridge and existing structures like the London Underground. For more information on the Lake Rockwell Dam project, be sure to check out our case study.

Abstract-Design and application of terahertz metamaterial sensor based on DSRRs in clinical quantitative detection of carcinoembryonic antigen

Ning Cui, Min Guan, Mengke Xu, Weihao Fang, Yang Zhang, Chenfeng Zhao, and Yiping Zeng

(a) Schematic diagram of THz MMs biosensor chip; (b) Detection principle and the equivalent circuit for the DSRRs. (The capacitance of substrates and sample are expressed as 𝐶sub$C\text{sub}$ and 𝐶sam$C\text{sam}$, respectively. 𝐿𝑠$Ls$ is expressed as inductance of DSRRs.)

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-11-16834

The terahertz (THz) metamaterial biosensor has great potential for label-free and rapid specificity testing. Here, we designed two highly sensitive structures to detect the carcinoembryonic antigen (CEA) of the cancer biomarker in early stages. There was about 29 GHz (500 ng/ml) resonance shift for CEA with an insert grate metamaterial, which was consistent with simulation results. Moreover, the concentration of CEA was gained through the relationship between the cancer marker concentration and frequency shift (Δƒ). Our design and detection methods may provide a potential route for the early warning stages of cancer.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-THz Precoding for 6G: Applications, Challenges, Solutions, and Opportunities

ingbo Tan, Linglong Dai

https://arxiv.org/abs/2005.10752

Benefiting from the ultra-wide bandwidth, terahertz (THz) communication is becoming a promising technology for future 6G networks. For THz communication, precoding is an essential technique to overcome the severe path loss of THz signals in order to support the desired coverage. In this article, we systematically investigate the dominant THz precoding techniques for future 6G networks, with the highlight on its key challenges and opportunities. Specifically, we first illustrate three typical THz application scenarios including indoor, mobile, and satellite communications. Then, the major differences between millimeter-wave and THz channels are explicitly clarified, based on which we reveal the key challenges of THz precoding, such as the distance-dependent path loss, the beam split effect, and the high power consumption. To address these challenges, three representative THz precoding techniques, i.e., analog beamforming, hybrid precoding, and delay-phase precoding, are extensively investigated in terms of their different structures, designs, most recent results, pros and cons. We also provide simulation results of spectrum and energy efficiencies to compare these typical THz precoding schemes to draw some insights for their applications in future 6G networks. Finally, several important open issues and the potential research opportunities, such as the use of reconfigurable intelligent surface (RIS) to solve the THz blockage problem, are pointed out and discussed.

Abstract-Terahertz spectral analysis of different electrolytes

Yi-Wei Wen, Bo Su, Jia-Hui Wang, Guo-Yang Wang, Ya-Xiong Wu, Jing-Suo He, Cun-Lin Zhang,

 https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-59/issue-5/055107/Terahertz-spectral-analysis-of-different-electrolytes/10.1117/1.OE.59.5.055107.short

Terahertz (THz) technology has become popular worldwide as a new approach to detecting biomolecules because the vibrational and rotational energy levels of many biomolecules fall in the THz band and because the THz wave has the characteristics of low electronic energy, which will not damage the samples to be measured. Many biomolecules need to maintain their biological activity in liquid environment. However, as a polar molecule, water has a strong absorption of THz wave, which is mainly because the vibration frequency of hydrogen bond in aqueous solution is within the THz frequency range. Therefore, the best solution is to reduce the action distance between the aqueous solution and THz wave and control it within 100  μm. Microfluidic chips can meet such requirements. Therefore, the combination of THz technology and microfluidic technology can study the dynamic characteristics of biomolecules in an aqueous solution. The microfluidic chip was fabricated using ZEONOR 1420Rs. The THz transmittance of the material can exceed 95%. The depth of the microchannel in the microfluidic chip is 50  μm. In addition, the chip has the characteristics of good airtightness, portability, convenient disassembling, and reusability. Seventeen kinds of electrolytes were tested with the chip. The results show that the THz spectral intensity of electrolyte composed of different anions and cations, so the spectral characteristics of other electrolyte solutions can be obtained according to the spectral information of these detected ions.

© 2020 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2020/$28.00 © 2020 SPIE

Abstract-Super terahertz phase shifter achieving high transmission and large modulation depth

Shuai Li, Jing Wang, Hao Tian, Li Li, Jianlong Liu, Guan Chao Wang, Jiaojiao Gao, Chengpeng Hu, and Zhongxiang Zhou

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-10-2834

We propose an industrial-grade liquid-crystal-based terahertz (THz) 2π-phase shifter with predictable ultra-high amplitude transmittance. The phase retardation reaches 360.5° at 1.68 THz by analyzing the birefringence of liquid crystal (LC), and the amplitude transmittance in 0.3–1.5 THz is over 83%. More than 91.5% transmittance can be reached by decreasing the scattering of the THz wave in the dynamic deflection process of LC molecules, and that is close to the transmittance limit of quartz-based devices. This millimeter-thick phase shifter reaches full phase modulation and ultra-high transmittance in a broad THz band, is easy to be integrated in a quasi-optical system with a compact size and can be utilized as a wave plate, even an element in a THz phased array.

© 2020 Optical Society of America

Abstract-System-theoretical modeling of terahertz time-domain spectroscopy with ultra-high repetition rate mode-locked lasers

Kevin Kolpatzeck, Xuan Liu, Kai-Henning Tybussek, Lars Häring, Marlene Zander, Wolfgang Rehbein, Martin Moehrle, Andreas Czylwik, and Jan C. Balzer

 Block diagram of a fiber-coupled THz-TDS setup. The optical output signal of the mode-locked laser source is distributed to a terahertz emitter (THz Tx) and, through a variable delay line, to a terahertz detector (THz Rx). The terahertz radiation generated by the emitter is transmitted through a sample and focused into the detector

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-11-16935

Terahertz time-domain spectroscopy (THz-TDS) systems based on ultra-high repetition rate mode-locked laser diodes (MLLDs) and semiconductor photomixers show great potential in terms of a wide bandwidth, fast acquisition speed, compactness, and robustness. They come at a much lower total cost than systems using femtosecond fiber lasers. However, to date, there is no adequate mathematical description of THz-TDS using a MLLD. In this paper, we provide a simple formula based on a system-theoretical model that accurately describes the detected terahertz spectrum as a function of the optical amplitude and phase spectrum of the MLLD and the transfer function of the terahertz system. Furthermore, we give a simple yet exact relationship between the optical intensity autocorrelation and the detected terahertz spectrum. We theoretically analyze these results for typical optical spectra of MLLDs to quantify the effect of pulse chirp on the terahertz spectrum. Finally, we confirm the validity of the model with comprehensive experimental results using a single-section and a two-section MLLD in a conventional THz-TDS system.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-A multi-purpose sensor based on plasmon-induced transparency in the terahertz range

Author links open overlay pane
Ladan Akbari, Kambiz Abed,


https://www.sciencedirect.com/science/article/pii/S1386947720304987

In this paper, an insulator-semiconductor-insulator plasmonic waveguide is proposed based on InSb in the terahertz range. The proposed plasmonic waveguide is an integrated temperature and refractive index sensor. The plasmon-induced transparency used in this integrated sensor reduces the sensor bandwidth by coupling two rolled-up micro-tubes. The sensitivity of the proposed sensor for temperature and refractive index can reach 4388 nm/K and 149.1 μm/RIU, respectively. The sensitivity of the sensor for refractive index is at least 805.95% larger than that of our previous work and the figure of merit is the order of 41.3. The proposed sensor has a wide range of potential lab-on-chip applications and can measure the variations of temperature and refractive index in the material under sensing.

Abstract-Real-time terahertz imaging with a single-pixel detector

Rayko Ivanov Stantchev, Xiao Yu, Thierry Blu, Emma Pickwell-MacPherson, 



https://www.nature.com/articles/s41467-020-16370-x

Terahertz (THz) radiation is poised to have an essential role in many imaging applications, from industrial inspections to medical diagnosis. However, commercialization is prevented by impractical and expensive THz instrumentation. Single-pixel cameras have emerged as alternatives to multi-pixel cameras due to reduced costs and superior durability. Here, by optimizing the modulation geometry and post-processing algorithms, we demonstrate the acquisition of a THz-video (32 × 32 pixels at 6 frames-per-second), shown in real-time, using a single-pixel fiber-coupled photoconductive THz detector. A laser diode with a digital micromirror device shining visible light onto silicon acts as the spatial THz modulator. We mathematically account for the temporal response of the system, reduce noise with a lock-in free carrier-wave modulation and realize quick, noise-robust image undersampling. Since our modifications do not impose intricate manufacturing, require long post-processing, nor sacrifice the time-resolving capabilities of THz-spectrometers, their greatest asset, this work has the potential to serve as a foundation for all future single-pixel THz imaging systems.

Abstract-Graphene-embedded coding metasurface for dynamic terahertz manipulation

Chen Zhou, Xiao-qing Peng, Jiu-sheng Li

https://www.sciencedirect.com/science/article/abs/pii/S0030402620307737

With the rapid development of terahertz wave technology and application systems, the dynamic manipulation of terahertz radiation is highly needed. We have investigated the performances of a graphene-embedded coding metasurface that can dynamically control the terahertz wave transmission. The coding element consists of gold substrate, silicon-polyimide interlayer and the top graphene-embedded metallic pattern that can realize abrupt reflection phase shift by adjusting the graphene Fermi level. Especially, by changing the Fermi energy of the graphene through bias voltage and pre-designed coding sequence, the new coding metasurface structure can control the reflected terahertz wave beams to various directions. The method brings us much freedom in design of terahertz wave manipulation device.