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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Giant Dual-Mode Graphene-Based THz Modulator
摘要： We report a high-performance terahertz (THz) modulator with dual-operation mode. For the pulse operation mode, the proposed THz modulator has the advantage of high modulation depth (MD) and can operate in a broadband frequency range. We have experimentally achieved a MD larger than 90% for the fifth-order pulse THz echo at 0.8 THz and the MD stays larger than 75% in a broadband frequency range larger than 1 THz. While, for the coherent operation mode, the Fabry-Perot (F-P) interference effect has been taken into consideration and a MD larger than 75% at 0.76 THz has also been realized.
关键词： dual-operation mode,terahertz modulator,modulation depth,Fabry-Perot interference,graphene
更新于2025-09-11 14:15:04
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A Low-Profile and High-Gain Frequency Beam Steering sub-THz Antenna Enabled by Silicon Micromachining
摘要： A very low-profile sub-THz high-gain frequency beam steering antenna, enabled by silicon micromachining, is reported for the first time in this paper. The operation bandwidth of the antenna spans from 220 GHz to 300 GHz providing a simulated field of view of 56?. The design is based on a dielectric filled parallel-plate waveguide (PPW) leaky-wave antenna fed by a pillbox. The pillbox, a two-level PPW structure, has an integrated parabolic reflector to generate a planar wave front. The device is enabled by two extreme aspect ratio, 16 mm x 16 mm large perforated membranes, which are only 30 μm thick, that provide the coupling between the two PPWs and form the LWA. The micromachined low-loss PPW structure results in a measured average radiation efficiency of ?1 dB and a maximum gain of 28.5 dBi with an input reflection coefficient below ?10 dB. The overall frequency beam steering frontend is extremely compact (24 mm x 24 mm x 0.9 mm) and can be directly mounted on a standard WM-864 waveguide flange. The design and fabrication challenges of such high performance antenna in the sub-THz frequency range are described and the measurement results of two fabricated prototypes are reported and discussed.
关键词： beam steering,leaky-wave antennas,silicon on insulator,terahertz radiation,silicon micromachining,quasi-optics,submillimeter-wave antennas
更新于2025-09-11 14:15:04
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InAs/GaAs Quantum Dot Dual-Mode Distributed Feedback Laser Towards Large Tuning Range Continuous-Wave Terahertz Application
摘要： In this paper, a laterally coupled distributed feedback (LC-DFB) laser based on modulation p-doped multiple InAs/GaAs quantum dot (QD) structures has been fabricated. The device exhibits a high side-mode suppression ratio (SMSR) of > 47 dB and a high thermal stability of dλ/dT = 0.092 nm/K under continuous-wave (CW) operation, which is mainly attributed to the high material gain prepared by modulation p-doping and rapid thermal annealing (RTA) process, and the significantly reduced waveguide losses by shallow-etched gratings and its close proximity to the laser ridge feature in the LC-DFB laser. With this superior performance of the DFB laser, the wide tunable dual-wavelength lasing operation has been obtained by delicately defining different periods for the grating structures on the two sides of the laser ridge or combining the reduced laser cavity length. The wavelength spacing between the two lasing modes can be flexibly tuned in a very wide range from 0.5 to 73.4 nm, corresponding to the frequency difference from 0.10 to 14 THz, which is the largest tuning range by the utilization of single device and hence providing a new opportunity towards the generation of CW THz radiation.
关键词： Semiconductor lasers,Lasers,Distributed feedback,Optoelectronics,Terahertz imaging,Quantum well, wire, and dot devices
更新于2025-09-11 14:15:04
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[IEEE 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) - New Delhi, India (2019.3.9-2019.3.15)] 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) - Near-field vertical coupling between terahertz photonic crystal waveguides
摘要： We demonstrate near-field coupling between terahertz photonic crystal waveguides in the out-of-plane dimension, with no direct physical contact, by making use of coupled-line techniques. Efficient transfer (i.e. ≈ 80%) of terahertz power from one waveguide to another is experimentally achieved. Thereafter, multi-Gbps data is successfully transmitted via this near-field link. This study can be considered a step towards practical connectors between terahertz photonic crystal waveguide circuits.
关键词： near-field coupling,photonic crystal waveguides,multi-Gbps data transmission,terahertz,coupled-line techniques
更新于2025-09-11 14:15:04
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Metamaterials and Metasurfaces || Electron Beam-Induced Directional Terahertz Radiation from Metamaterials
摘要： We have numerically analyzed an electron beam (e-beam)-induced directional terahertz (THz) radiation from metamaterials. Here, we used metallic grating structures with graded depths, in which only one-way surface mode can be supported based on the spoof surface plasmon polariton (spoof SPP) concept and gives unique directional THz radiation. For numerical analysis, we used a simplified particle-in-cell (PIC) finite-difference time-domain (FDTD) method. First, we describe our simplified PIC-FDTD method in detail. Then, we show our results on the e-beam-induced directional THz radiation from graded grating with graded depths. By passing pulsed (bunched) e-beam along the grating surface, directional THz radiations are obtained from one side of the grating with shallower grooves. The direction of these radiations can be switched backward or forward by making the groove depth deeper or shallower. The spectra of these directional radiations are wide band and contain multiple sharp peaks. The deepest and the shallowest groove depths determine the lowest and the highest frequency of the radiation band, respectively. These unique radiation characteristics cannot be explained by the conventional Smith-Purcell radiation and should be attributed to the spoof SPP that originates from different locations on the graded grating.
关键词： graded grating,Smith-Purcell radiation,THz,particle-in-cell finite-difference time-domain,metamaterial,PIC-FDTD,electron beam,terahertz
更新于2025-09-11 14:15:04
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Fluorinated Organic Electro-Optic Quinolinium Crystals for THz Wave Generation
摘要： Fluorinated electro-optic crystals with state-of-the-art second-order nonlinear optical response and excellent characteristics for terahertz (THz) wave generation are reported. The fluorinated organic ionic crystals consist of optically highly nonlinear fluorinated HM6FQ (6-fluoro-2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) or HM7FQ (7-fluoro-2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) cations and 4-methylbenzenesulfonate (T) counter anions. Compared to benchmark electro-optic crystals based on nonfluorinated HMQ (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) cations, introducing fluorine substituent on HM6FQ cations creates additional hydrogen bonds (ArF···HC). Such a molecular engineering leads to an enhanced thermal stability and significant modulations of phonon vibrational modes of crystals in THz frequency region, while excellent π–π stacking and space filling characteristics of HM6FQ cations in crystals lead to state-of-the-art diagonal component of the macroscopic nonlinear optical susceptibility, similar to the case of HMQ cations. HM6FQ-based crystals exhibit a very high optical-to-THz conversion efficiency, comparable to benchmark HMQ-based crystals. In addition, due to additional hydrogen bonds induced by fluorine substituents, the spectral shape of the generated THz wave is remarkably modified; e.g., the largest spectral gap is near 1.5 and 2.0 THz for HM6FQ- and HMQ-based crystals, respectively. The fluorinated cationic engineering on nonlinear optical crystals having benchmark nonlinear optical response is, as far as is known, reported for the first time.
关键词： organic crystals,nonlinear optics,terahertz waves,electro-optics
更新于2025-09-11 14:15:04
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[IEEE 2018 5th International Conference on Systems and Informatics (ICSAI) - Nanjing (2018.11.10-2018.11.12)] 2018 5th International Conference on Systems and Informatics (ICSAI) - Modeling of Multilayer Graphene at Terahertz with Vector Fitting Method
摘要： Graphene is a promising carbon nanomaterial, and multilayer graphene are more interesting than the monolayer one. The dispersion of multilayer graphene at terahertz (THz) leads to difficulties in transient electromagnetic simulation, e.g. the time domain integral equation (TDIE) method. This paper aims to achieve accurate fitting of multilayer graphene dispersive surface conductivity/impedance over ultra wideband THz frequencies. Graphene surface conductivity/impedance at THz is calculated by the Kubo formula. Thereafter, the surface conductivity and impedance is approximated by vector fitting method with expansions of several pairs of poles and residues. Numerical results are provided to validate the proposed method. Multilayer graphene time domain surface impedance which is used in the impedance boundary condition (IBC) for TDIE can be obtained readily by the inverse Fourier transform of its frequency domain counterpart.
关键词： terahertz,vector fitting,impedance,multilayer graphene
更新于2025-09-11 14:15:04
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Resonant Tunneling Diode (RTD) Terahertz Active Transmission Line Oscillator with Graphene-Plasma Wave and Two Graphene Antennas
摘要： This study describes the design of a resonant tunneling diode (RTD) oscillator (RTD oscillator) with a RTD-gated-graphene-2DEF (two dimensional electron fluid) and demonstrates the functioning of this RTD oscillator through a transmission line simulation model. Impedance of the RTD oscillator changes periodically when physical dimension of the device is of considerable fraction of the electrical wavelength. As long as impedance matching is achieved, the oscillation frequency is not limited by the size of the device. An RTD oscillator with a graphene film and negative differential resistance (NDR) will produce power amplification. The positive electrode of the DC power supply is modified and designed as an antenna. So, the reflected power can also be radiated to increase RTD oscillator output power. The output analysis shows that through the optimization of the antenna structure, it is possible to increase the RTD oscillator output to 22 mW at 1.9 THz and 20 mW at 6.1 THz respectively. Furthermore, the RTD oscillator has the potential to oscillate at 50 THz with a matching antenna.
关键词： transmission line model,RTD-gated-graphene-2DEF,resonant tunneling diode (RTD),graphene-plasma,two-dimensional electron fluid (2DEF),resonant tunneling diode oscillator (RTD oscillator),terahertz
更新于2025-09-11 14:15:04
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Selective terahertz emission due to electrically excited 2D plasmons in AlGaN/GaN heterostructure
摘要： Terahertz radiation emission from an electrically excited AlGaN/GaN heterostructure with a surface metal grating was studied under conditions of two-dimensional (2D) electron heating by the lateral electric field. Intensive peaks related to nonequilibrium 2D plasmons were revealed in the terahertz emission spectra with up to 4 times selective amplification of the radiation emission in the vicinity of 2D plasmon resonance. This selective emission was shown to be frequency-controllable by the grating period. Exact spectral positions of the 2D plasmon resonances were preliminarily experimentally detected with the help of equilibrium transmission spectra measured at various temperatures. The resonance positions are in a satisfactory agreement with the results of theoretical simulation of the transmission spectra performed using a rigorous solution of Maxwell’s equations. The effective temperature of hot 2D electrons was determined by means of I–V characteristics and their analysis using the power balance equation. It was shown that for a given electric field, the effective temperature of nonequilibrium 2D plasmons is close to the hot 2D electron temperature. The work may have applications in GaN-based electrically pumped emitters of terahertz radiation.
关键词： electrical excitation,terahertz radiation,metal grating,AlGaN/GaN heterostructure,2D plasmons
更新于2025-09-11 14:15:04
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Broadband Linear-to-Circular Polarization Conversion Enabled by Birefringent Off-Resonance Reflective Metasurfaces
摘要： Due to the scarcity of circular polarization light sources, linear-to-circular polarization conversion is required to generate circularly polarized light for a variety of applications. Despite significant past efforts, broadband linear-to-circular polarization conversion remains elusive particularly in the terahertz and midinfrared frequency ranges. Here we propose a novel mechanism based on coupled mode theory, and experimentally demonstrate at terahertz frequencies that highly efficient (power conversion efficiency approaching unity) and ultrabroadband (fractional bandwidth up to 80%) linear-to-circular polarization conversion can be accomplished by the judicious design of birefringent metasurfaces. The underlying mechanism operates in the frequency range between well separated resonances, and relies upon the phase response of these resonances away from the resonant frequencies, as well as the balance of the resonant and nonresonant channels. This mechanism is applicable for any operating frequencies from microwave to visible. The present Letter potentially opens a wide range of opportunities in wireless communications, spectroscopy, and emergent quantum materials research where circularly polarized light is desired.
关键词： linear-to-circular polarization conversion,midinfrared,birefringent metasurfaces,terahertz,broadband
更新于2025-09-11 14:15:04