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Low Voltage Graphene-Based Amplitude Modulator for High Efficiency Terahertz Modulation
摘要： In this paper, a high-e?ciency terahertz amplitude modulation device based on a ?eld-e?ect transistor has been proposed. The polarization insensitive modulator is designed to achieve a maximum experimental modulation depth of about 53% within 5 V of gate voltages using monolayer graphene. Moreover, the manufacturing processes are inexpensive. Two methods are adopted to improve modulation performance. For one thing, the metal metamaterial designed can e?ectively enhance the electromagnetic ?eld near single-layer graphene and therefore greatly promote the graphene’s modulation ability in terahertz. For another, polyethylene oxide-based electrolytes (PEO:LiClO4) acts as a high-capacity donor, which makes it possible to dope single-layer graphene at a relatively low voltage.
关键词： solid electrolyte,terahertz,single-layer graphene,transmittance,metamaterial,amplitude modulation,?eld-e?ect transistor
更新于2025-09-23 15:21:01
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Terahertz Photoconductivity in Graphene in a Magnetic Field
摘要： The terahertz photoconductivity in epitaxial graphene grown on SiC substrates is investigated in a magnetic field. The magnetic-field dependence of the photoresponse signal amplitude is examined at different electron densities, bias currents, and terahertz radiation intensities. The experimental results are explained well by a photoconductivity mechanism based on the heating of electrons by terahertz radiation. A strong increase in the photoconductivity signal with increasing magnetic field caused by an increase in the relaxation time due to the suppression of electron-electron scattering is observed.
关键词： terahertz radiation,photoconductivity,magnetic field,graphene
更新于2025-09-23 15:21:01
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Terahertz plasma wave localization and velocity control in tapered double-layer graphene heterostructure
摘要： Terahertz plasma wave (plasmon) localization and velocity control in tapered heterostructure (taper) with double-layer graphene were numerically studied. We employ a simple rigorous theoretical model to find out the plasmon localization length and energy velocity values along the tapered structure. It is shown that the plasmon decelerates while moving from the taper apex and the deceleration process is accompanied with increase of the plasmon wave localization. While moving along the structure from the taper apex, the plasmon energy velocity as well as the plasmon localization length can become nearly an order of magnitude smaller as compared to the values near the taper apex.
关键词： plasmon localization,Terahertz plasma wave,tapered heterostructure,velocity control,double-layer graphene
更新于2025-09-23 15:21:01
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THz Wave Emission From ZnTe Nano-Colloidal Aqueous Dispersion Irradiated by Femtosecond Laser
摘要： THz wave emission from ZnTe nano-colloidal aqueous dispersion flow (the particle size is 5-nm in diameter, the flow thickness is 17 μm) with two different particle densities (1.60 mmol/L and 1.07 mmol/L) was measured by time-domain spectroscopy (TDS) under femtosecond laser irradiation (>35 fs/transform-limited, 800 nm, horizontally-polarized, 0.5 kHz) in air. Intensity increase and peak shift in the TDS signal wave-form if compared with distilled water indicate that THz wave emission is induced in ZnTe nano-particles in the aqueous dispersion.
关键词： Terahertz,femtosecond laser,ZnTe nano-colloid
更新于2025-09-23 15:21:01
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Self-focused amplitude modulated super Gaussian laser beam in plasma and THz radiation with high efficiency
摘要： Based on self- focusing of an amplitude modulated super Gaussian laser beam in preformed ripple density plasma, one scheme can be proposed for generating terahertz (THz) radiation at the modulation frequency when pondermotive nonlinearity is operative. The eikonal in paraxial ray approximation (PRA) along with higher order terms in the expansion of the dielectric function have been taken into account. Intensity variation in the direction transverse to the propagated laser causes a pondermotive force which generates transient transverse nonlinear current. At the modulation frequency, the mentioned current drives radiation in THz domain. Therefore, comparing to simple PRA, inclusion of terms with higher order enhances beam self-focusing, THz radiation field and, efficiency. In addition, the degree of the self-focusing is reduced in higher laser beam orders and has changed by the modulation index and the time. Here, by considering higher order paraxial ray approximation and optimizing laser beam and ripple density, plasma parameters are investigated and the efficiency of THz radiation reaches up to 6.5%. This method can be applied for the efficient types of THz radiation.
关键词： Efficiency,Self-focusing,Terahertz radiation,Super Gaussian beam,Amplitude modulated
更新于2025-09-23 15:21:01
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[IEEE 2018 11th UK-Europe-China Workshop on Millimeter Waves and Terahertz Technologies (UCMMT) - HangZhou, China (2018.9.5-2018.9.7)] 2018 11th UK-Europe-China Workshop on Millimeter Waves and Terahertz Technologies (UCMMT) - A Fabry-Perot Resonator Antenna based on Graphene Patch Array
摘要： In order to achieve a high directivity antenna for terahertz, an improved Fabry-Perot resonator antenna based on graphene is proposed. The antenna consists of a graphene patch array on a grounded dielectric and a rectangle waveguide. According to the theory of Fabry-Perot resonant cavity, the directivity of antenna will increase obviously by choosing proper chemical potential of graphene and appropriate distance of resonant cavity. The radiation pattern of antenna also changes with the chemical potential.
关键词： Terahertz,Antenna,Graphene,tunability,Fabry-Perot resonator
更新于2025-09-23 15:21:01
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Proposal for a symmetrical petal core terahertz waveguide for terahertz wave guidance
摘要： Countering the terahertz wave applications ‘inefficient transmission’ calls for rapid development in terahertz waveguides that could simultaneously minimize confinement loss, chromatic dispersion and maximize the fraction of power. Here, a new kind of symmetrical petal hollow core terahertz waveguide based on cyclic olefin homopolymer is proposed to achieve low confinement loss, low chromatic dispersion and a high fraction of power. In this designed waveguide, a symmetrical petal-shaped air hole is treated as the core and circular air holes arranged as sunflower-type are inserted in the cladding. The guiding characteristics of the designed waveguide are simulated and analyzed based on the finite element method with perfectly matched layer boundary condition. Based on the optimum structure parameters, it exhibits a minimum confinement loss of 0.0089 dB/cm at 2.58 THz and a < 0.07 dB/cm bandwidth spanning across 2.51 - 2.71 THz. Furthermore, in the same frequency region, the high core power fraction is above 93%, and the group velocity dispersion values are lower than 0.6 ps/THz/cm.
关键词： petal hollow core,terahertz waveguide,efficient transmission
更新于2025-09-23 15:21:01
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Nonlinear Charge Transport in InGaAs Nanowires at Terahertz Frequencies
摘要： We probe the electron transport properties in the shell of GaAs/In0.2Ga0.8As core/shell nanowires at high electric fields using optical pump/THz probe spectroscopy with broadband THz pulses and peak electric fields up to 0.6 MV/cm. The plasmon resonance of the photoexcited charge carriers exhibits a systematic redshift and a suppression of its spectral weight for THz driving fields exceeding 0.4 MV/cm. This behavior is attributed to the intervalley electron scattering that results in the doubling of the average electron effective mass. Correspondingly, the electron mobility at the highest fields drops to about half of the original value. We demonstrate that the increase of the effective mass is nonuniform along the nanowires and takes place mainly in their middle part, leading to a spatially inhomogeneous carrier response. Our results quantify the nonlinear transport regime in GaAs-based nanowires and show their high potential for development of nanodevices operating at THz frequencies.
关键词： Localized Plasmon,Intervalley Scattering,Nanowire,Terahertz (THz)
更新于2025-09-23 15:21:01
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Ultrasensitive Ambient-Stable SnSe<sub>2</sub>-based Broadband Photodetectors for Room-Temperature IR/THz Energy conversion and Imaging
摘要： The advent of tin diselenide (SnSe2) enables novel pathways for optoelectronics, due to its reduced cost, ultralow thermal conductivity and high potential for thermoelectricity. To date, SnSe2-based optoelectronic devices have been focused on the visible and infrared range of the electromagnetic spectrum, with efficiency sharply decreasing at longer wavelength. Here, we present SnSe2 photodetectors with exfoliated SnSe2 nanosheets extended in the range of THz frequency, exhibiting high responsivity (170 V W-1), fast speed(2.2 μs), as well as room-temperature operation, based on efficient production of hot electrons under deep-subwavelength electromagnetic focus, which outperform thermal-based photodetectors. The outstanding ambient stability of our broadband photodetectors in a timescale of months is due to the chemical inertness of stoichiometric SnSe2 crystals, validated by surface-science experiments. Our results demonstrate the suitability of SnSe2for multispectral sensing and real-time imaging. Our SnSe2-based detectors show high-contrast imaging from terahertz (THz) up to visible.
关键词： Photothermoelectric,Terahertz,Tin diselenide,Broadband photodetector
更新于2025-09-23 15:21:01
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Ultrafast response of harmonic modelocked THz lasers
摘要： The use of fundamental modelocking to generate short terahertz (THz) pulses and THz frequency combs from semiconductor lasers has become a routine affair, using quantum cascade lasers (QCLs) as a gain medium. However, unlike classic laser diodes, no demonstrations of harmonic modelocking, active or passive, have been shown in THz QCLs, where multiple pulses per round trip are generated when the laser is modulated at the harmonics of the cavity’s fundamental round-trip frequency. Here, using time-resolved THz techniques, we show for the ?rst time harmonic injection and mode-locking in which THz QCLs are modulated at the harmonics of the round-trip frequency. We demonstrate the generation of the harmonic electrical beatnote within a QCL, its injection locking to an active modulation and its direct translation to harmonic pulse generation using the unique ultrafast nature of our approach. Finally, we show indications of self-starting harmonic emission, i.e., without external modulation, where the QCL operates exclusively on a harmonic (up to its 15th harmonic) of the round-trip frequency. This behaviour is supported by time-resolved simulations of induced gain and loss in the system and shows the importance of the electronic, as well as photonic, nature of QCLs. These results open up the prospect of passive harmonic modelocking and THz pulse generation, as well as the generation of low-noise microwave generation in the hundreds of GHz region.
关键词： harmonic modelocking,ultrafast response,THz QCLs,terahertz pulses,quantum cascade lasers
更新于2025-09-23 15:21:01