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Actively tunable toroidal excitations in graphene based terahertz metamaterials
摘要： Toroidal dipoles, unlike electric and magnetic dipoles, are formed due to currents flowing on the surface of a torus along its meridians. We investigate the toroidal dipole response in a graphene based infinite 2D array of terahertz (THz) meta-material (MM) and report the active tuning of the toroidal resonances. Each metamolecule in our proposed MM configuration consists of two joint split ring resonators (SRRs) made up of graphene material with two gaps in each resonator. We examine actively tunable response of the toroidal excitations with respect to a change in the Fermi energy of graphene material. The toroidal effect is elaborated using surface current and magnetic field profiles at the resonance frequency of the metamolecule structure. The modulation of the metamaterial toroidal response and effect on Q factor is further examined by changing the relaxation time of graphene. The excitation of toroidal resonances at terahertz frequencies and their dynamic control could be significant in designing efficient tunable modulators, filters and sensors.
关键词： terahertz,toroidal resonance,metamaterial,graphene
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP) - Bochum, Germany (2019.7.16-2019.7.18)] 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP) - Characterization and Application of a Commercially Available Laser Diode in a THz System
摘要： In this work, we characterize a commercially available laser diode. The complex optical spectrum shows that most of the laser modes have a fixed phase relation, i.e. the laser is mode-locked. By choosing a single-mode fiber with appropriate length, the intrinsic chirp of the laser can be compensated. As a result, the amplitude of the detected THz signal is increased by a factor of 16.
关键词： mode-locked laser diodes,terahertz technology,time-domain spectroscopy
更新于2025-09-16 10:30:52
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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) - High Conversion Efficiency in a System “Nonlinear-Optical Crystal Partially Filling the Cross Section of a Rectangular Waveguide”
摘要： It is shown that terahertz radiation (0.1-3 THz) can be effectively generated via optical rectification of femtosecond laser pulses in a system of a “nonlinear-optical crystal partially filling the cross section of a rectangular metal waveguide”. The numerical calculations for the phase-matching in LiNbO3, ZnTe, DAST and GaSe nonlinear optical crystals have been performed. The influence of THz radiation absorption on the efficiency of generation of coherent THz radiation in the system has been investigated.
关键词： optical rectification,femtosecond laser pulses,phase-matching,nonlinear-optical crystal,terahertz radiation
更新于2025-09-16 10:30:52
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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) - Modulation Behaviors, Conductivities, and Carrier Dynamics of Single and Multilayer Graphenes
摘要： Time domain and time resolved terahertz studies of single- and multi-layer graphene (SLG and MLG) samples and modulator devices will be presented. A high performance up to 100% of modulators were observed with the devices even at very low voltages. High modulation depth over such a broad spectrum and simple device structure brings significant importance toward application of this type of device in THz and related technologies. In addition, conductivities of SLG and MLG devices were also investigated and a change in behavior was observed as the layer thickness increased. The charge carriers dynamics of the samples with pulp fluence and color was also highly interesting.
关键词： modulator,carrier dynamics,conductivity,terahertz,graphene
更新于2025-09-16 10:30:52
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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) - Asymmetric Dual Grating Gate Graphene-based THz detectors
摘要： We report on detection of terahertz radiation by using asymmetric dual-grating gates graphene-based FET. The graphene sheet was sandwiched between two layers of hexagonal Boron Nitride (h-BN) to avoid interaction with the substrate and enhance carrier mobility. Asymmetric dual metal gates were processed on the top of the upper h-BN layer. The devices were excited with terahertz radiation at frequencies of 0.15 and 0.3 THz and a clear photocurrent was observed from 4K up to room temperature.
关键词： FET,detectors,h-BN,terahertz,graphene
更新于2025-09-16 10:30:52
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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) - Tri-band Linear to Circular Polarization Converter based on Transmissive Metasurfaces
摘要： Multi-band operation for terahertz wireless systems is a challenging problem. We propose a tri-band linear to circular polarization converter in the terahertz regime using metasurfaces in transmission modes. The converter is composed of bi-layered metasurfaces separated by a dielectric spacer. Three bands (0.54-0.804, 1.904-2.476, and 2.96-3.884 THz) of linear to circular polarization conversion (LCPC) are achieved due to the superposition of the two transmitted components with a near 90° phase difference. Idea is verified by HFSS and paves a way to the design of multi-band transmissive linear to circular polarization converter.
关键词： linear to circular polarization converter,transmission modes,metasurfaces,terahertz,Multi-band operation
更新于2025-09-16 10:30:52
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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) - Terahertz Emission due to Radiative Decay of Hot 2D Plasmons in AlGaN/GaN Heterojunction
摘要： Emission of terahertz radiation from a AlGaN/GaN/Al2O3 heterostructure with a surface metal grating is investigated under conditions of 2D electron heating in a lateral electric field. The studies are performed under essentially non-equilibrium conditions when the effective temperatures of 2D electrons and 2D plasmons are several times higher than the lattice temperature. This makes it possible to observe and explore high-quality peaks of intense THz radiation corresponding to 2D plasmon resonance.
关键词： electron heating,AlGaN/GaN heterojunction,radiation,terahertz,2D plasmons
更新于2025-09-16 10:30:52
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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) - High-resolution frequency and phase control of a terahertz laser
摘要： We report on the high-resolution frequency and phase control of a terahertz (THz) quantum cascade laser (QCL). The 2.0 THz QCL is locked to a stable microwave reference frequency via an all-fibre infrared frequency comb. The frequency of the QCL is controlled by optical injection and the phase is independently controlled by introducing a phase-lock loop that provides electronic feedback to the QCL, forming an optical injection phase locked loop (OIPLL). By implementing this, (1) the instrument limited linewidth of the locked QCL was <1Hz (2) for a fixed frequency, the phase of the THz QCL relative to the microwave reference frequency can be controlled within a range 0.3(cid:2).
关键词： optical injection phase locked loop,phase control,quantum cascade laser,frequency control,terahertz
更新于2025-09-16 10:30:52
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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) - Strong Anisotropic Photo-mixing Effect of Semi-Dirac Materials in the Terahertz Regime
摘要： Semi-Dirac materials such as a TiO2/VO2 have been shown to possess a parabolic energy-momentum dispersion in the x direction and linear dispersion in the y direction. This unique energy-momentum dispersion leads to many anisotropic effects. Here, we demonstrate a strong anisotropic photo-mixing effect in such systems which can be used to control the strength of the photo-response.
关键词： semi-Dirac system,momentum dispersion,anisotropic photo-mixing effect,terahertz regime
更新于2025-09-16 10:30:52
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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) - Electromagnetic-field analysis of diagonal-feedhorn antennas for terahertz-frequency quantum-cascade laser integration
摘要： we present an electromagnetic-field analysis of a terahertz-frequency quantum-cascade (THz QCL) integrated with a mechanically micro-machined waveguide cavity and diagonal feedhorn. A hybrid finite-element/Fourier transform approach enables analysis of both the near-field and far-field regions and is shown to agree well with experimental observations. The far-field antenna patterns show enhancement of the beam profile when compared with an unmounted QCL, in terms of beam divergence and side-lobe suppression ratio. Furthermore, we demonstrate integration of the QCL with dual diagonal feedhorns, enabling simultaneous access to both facets of the QCL, underpinning future integration with a satellite-based receiver and frequency-stabilization subsystem.
关键词： terahertz-frequency quantum-cascade laser,waveguide cavity,beam profile enhancement,electromagnetic-field analysis,diagonal feedhorn
更新于2025-09-16 10:30:52