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Spectral efficiency optimization for intelligent reflecting surface aided multi-input multi-output terahertz system
摘要： Intelligent reflecting surface (IRS) is considered as a promising application in terahertz (THz) communications since it is able to enhance the THz communication with no additional power consumptions. In this letter, we consider a downlink multi-input multi-output system, where a base station (BS) communicates to a user with the aid of the IRS. Our goal is to optimize the spectral efficiency by designing discrete phase-shifts at the IRS and the precoder at the BS, which is an intractable nonconvex optimization problem. To solve it, we approximate the problem into another form where we maximize the sum of path gains by designing the phase-shifts of the IRS, and we propose a cross-entropy based algorithm to search the optimal IRS phase-shifts matrix. After that, we use the classical singular value decomposition and water-filling solution to design the optimal precoder.
关键词： terahertz (THz) communication,intelligent reflecting surface (IRS),spectral efficiency
更新于2025-09-23 15:21:01
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Ultracompact and dynamically tunable plasmonic THz switch based on graphene microcavity metamaterial
摘要： We propose and discuss a compact and tunable plasmonic terahertz (THz) metamaterial switch based on graphene micro-cavity. Due to the joint effect of graphene plasmon resonances and Fabry–Perot oscillations, this metamaterial structure can be switched from the ON state to OFF state with the maximum intensity attenuation larger than 95% (ON–OFF ratio larger than 30 dB). The central frequency of the switch could be tuned in a wide frequency range from 3.6 to 9.6 THz by tuning the Fermi energies of the graphene patterns. Moreover, the metamaterial structure is valid for a wide range of incident angles of both transverse electric (TE) and transverse magnetic (TM) polarizations with the highest Q factor of 15.5. This investigation promises the development of high-performance, widely tunable THz switch in chip integrated photonic circuits without reconstructing the physical structures.
关键词： Terahertz,Switch,Graphene,Metasurface
更新于2025-09-23 15:21:01
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Beam Steering of a Terahertz Semi Bow Tie Antenna Using Parasitic Graphene Ribbons
摘要： In this paper, a reconfigurable beam-scanning planar antenna is proposed in terahertz frequencies. The presented structure consists of a semi bow tie antenna surrounded by circularly arranged parasitic pieces of graphene. The performance of the proposed antenna is investigated considering three different states where a PEC ground plane and a graphene ground layer with chemical potentials 0 (mode A) and 1 (mode B) are utilized at the bottom of the substrate. The proposed antenna is designed for utilization at a specific frequency of 1.2 THz in all these three states. The achieved antenna boresight and radiation pattern are altered through changing the conductivity of parasitic graphene elements and ground plane, which is obtained by controlling the corresponding chemical potential of the graphene segments. In addition, the parasitic graphene elements, located around the antenna, provide a high degree of freedom for altering the radiation pattern and antenna boresight. The parasitic elements operate as directors in modes A and B, whereas they act as reflectors in PEC ground state. Moreover, a high beam steering capability is obtained as chemical potentials of graphene elements are allocated between 0 and 1, whereas a PEC ground layer is employed at the bottom of the antenna. It should be noted that the gain and front-to-back ratio of the antenna are controlled using different chemical potentials of the graphene elements. A wide range of scan angles allocated between 0 and 180°, and toward the left and right directions in constant φ plane is achieved for the designed antenna.
关键词： Terahertz,Graphene,Reconfigurable,Beam steering,Antenna
更新于2025-09-23 15:21:01
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Simultaneous generation of two THz waves with bulk LiNbO3 and four THz waves with PPLN by coupled optical parametric generation
摘要： We present a theoretical research concerning simultaneous generation of two terahertz (THz) waves with bulk LiNbO3 and four THz waves with periodically poled LiNbO3 (PPLN) by coupled optical parametric generation (COPG). First, we investigate collinear phase matching of COPG generating two orthogonally polarized THz waves with two types of phase matching of o = e ? e and o = e ? o with bulk LiNbO3. The two orthogonally polarized THz waves are generated from stimulated polariton scattering (SPS) with A1 and E symmetric transverse optical (TO) modes in bulk LiNbO3, respectively. Then, we ?nd that perturbations of phase mismatch for o = e ? e and o = e ? o can be compensated by a same grating vector of PPLN. As a result, four THz waves are simultaneously generated with a PPLN crystal and a pump laser. We calculate third-order nonlinear optical coef?cients of o = e ? o generating THz waves from E symmetric TO modes. The intensities of four THz waves are calculated by solving coupled-wave equations. The calculation results demonstrate that four THz waves with high intensities can be simultaneously realized by COPG with existing laser technology and crystal fabrication technology.
关键词： Stimulated polariton scattering,Coupled optical parametric generation,Periodically poled LiNbO3,Terahertz wave
更新于2025-09-23 15:21:01
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Terahertz Optoelectronics in Graphene
摘要： Graphene has attracted considerable attention due to its extraordinary carrier transport, optoelectronic, and plasmonic properties originated from its gapless and linear energy spectra enabling various functionalities with extremely high quantum efficiencies that could never be obtained in any existing materials. This paper reviews recent advances in graphene optoelectronics particularly focused on the physics and device functionalities in the terahertz (THz) electromagnetic spectral range. Optical response of graphene is characterized by its optical conductivity and nonequilibrium carrier energy relaxation dynamics, enabling amplification of THz radiation when it is optically or electrically pumped. Current-injection THz lasing has been realized very recently. Graphene plasmon polaritons can greatly enhance the THz light and graphene matter interaction, enabling giant enhancement in detector responsivity as well as amplifier/laser gain. Graphene-based van der Waals heterostructures could give more interesting and energy-efficient functionalities.
关键词： graphene,plasmon,terahertz,laser,optoelectronics
更新于2025-09-23 15:21:01
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Durchblick mit Holografie
摘要： Bildgebung mit Terahertzstrahlung basiert bislang auf dem Abscannen eines Objekts mit einem Einzeldetektor. Mikrobolometer-Kameras erm?glichen nun eine Bildgebung wie mit jeder Kameratechnik. Fl?chendetektoren erlauben überdies den Einsatz holografischer Methoden. Trotz der gro?en Wellenl?nge reicht die dreidimensionale Ortsaufl?sung für Anwendungen in der Biomechanik.
关键词： Mikrobolometer-Kamera,Oberfl?chenstruktur,Terahertz-Strahlung,THz-Ptychografie,THz-Holografie,Fingerkuppe,Kontaktfl?che
更新于2025-09-23 15:21:01
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Terahertz Emission From an Exchange-Coupled Synthetic Antiferromagnet
摘要： We report on terahertz emission from Fe-Mn-Pt/Ru/Fe-Mn-Pt and Pt/Co-Fe-B/Ru/Co-Fe-B/Pt synthetic antiferromagnet (SAF) structures upon irradiation by a femtosecond laser; the former is via the anomalous Hall effect, whereas the latter is through the inverse spin Hall effect. The antiparallel alignment of the two ferromagnetic layers leads to a terahertz emission peak amplitude that is almost double that of a corresponding single-layer or bilayer emitter with the same equivalent thickness. In addition, we demonstrate by both simulation and experiment that terahertz emission provides a powerful tool to probe the magnetization reversal processes of individual ferromagnetic layers in a SAF structure, as the terahertz signal is proportional to the vector difference (M1 ? M2) of the magnetizations of the two ferromagnetic layers.
关键词： anomalous Hall effect,synthetic antiferromagnet,terahertz emission,magnetization reversal,inverse spin Hall effect
更新于2025-09-23 15:21:01
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Temperature Tunable Narrow-Band Terahertz Metasurface Absorber Based on InSb Micro-Cylinder Arrays for Enhanced Sensing Application
摘要： A narrow-band metasurface absorber (MSA) based on InSb micro-cylinder arrays has been proposed and investigated numerically, which could be believed to be applicable for both temperature and refractive index (RI) sensing in terahertz (THz) region. Distinct from previous designs, the proposed narrow-band MSA is only consisted of a sub-wavelength periodic micro-cylinder array based on the InSb material possessing an extremely thermosensitive relative permittivity which varies with the external environment temperature, and a gold ground-plane deposited on a glass substrate. Numerical simulation results indicate that the proposed MSA can achieve an absorbance of 99.9% at 1.8985 THz and the corresponding Q-factor is about 120.9 at room temperature (300 K). It is inferred that the narrow-band perfect absorption of the MSA could be contributed to the surface plasmon polariton (SPP) resonance mode excitation. Furthermore, the absorption property of the designed MSA is found to be highly sensitive to the RI value variations of the surrounding mediums and fluctuations of external environment temperature. Thus, the proposed MSA can be not only operated as a temperature sensor with a sensitivity of 2.13 GHz/K, but also a RI sensor with a sensitivity of 960 GHz/RIU (refractive index unit). Due to its high sensing performance, it can be believed that the narrow-band MSA has great potential applications in chemical, biological or other optoelectronic related areas.
关键词： terahertz region,Metasurface absorber,sensing,InSb,narrow-band
更新于2025-09-23 15:21:01
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Low-Terahertz Transparent Graphene-Based Absorber
摘要： A new, transparent, metal-free absorber, based on the use of multilayer graphene/dielectric laminates (GLs), is proposed for applications in the low-terahertz frequency range. The designed absorber has a total thickness of around 70 μm and consists of a front matching dielectric layer followed by a GL, a dielectric spacer and a back GL. The laminates are periodic structures constituted of graphene sheets separated by 50-nm-thick polyethylene terephthalate (PET) interlayers, while the matching layer and the spacer are one-quarter-wavelength thick and made of PET. The GLs are modeled as homogeneous-equivalent single layers (ESLs) characterized by their sheet resistances Rs. An innovative analytical method is proposed in order to select Rs values optimizing the electromagnetic wave absorption either in low-gigahertz or low-terahertz frequency range. The frequency spectra of the absorption, reflection and transmission coefficients are computed in the range up to 4 THz by using different values of Rs. Then, realistic Rs values of chemically doped graphene monolayers over PET substrates are considered. The designed absorbers are characterized by an absorption coefficient with a peak value of about 0.8 at the first resonant frequency of 1.1 THz, and a 1.4 THz bandwidth centered at 1.5 THz with reflection coefficient below - 10 dB. Moreover, the optical transmittance of the proposed absorbers are computed by means of the optical matrix theory and it is found to be greater than 86% in all the visible ranges.
关键词： absorption,reflection and transmission performance up to 4 THz,low-terahertz transparent absorber,transmission line approach,graphene-polyethylene terephthalate laminate,laminate effective medium model,optical transmittance in the visible range
更新于2025-09-23 15:21:01
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High-sensitivity biosensor for identification of protein based on terahertz Fano resonance metasurfaces
摘要： Terahertz metasurface biosensors have gained significant attention in biological field due to its label-free, real-time and in-situ detection properties. In this paper, a planar array of Fano asymmetric split ring resonators (ASRs) fabricated on 25 μm flexible polyimide substrate was proposed for new terahertz metasurface biosensors. It is shown that 160 GHz/RIU and 240 GHz/RIU refractive index sensitivity can be severally obtained near 0.81 and 1.13 THz transmission dips of the proposed system. Correspondingly, for biosensor samples that protein A/G, A/G + IgG were spotted on ASRs surface in our experiment, shifts of 8.9 GHz and 11.7 GHz, 17.6 GHz and 52.9 GHz toward low frequency were observed, respectively. These results illustrate high-sensitivity and label-free detection of proteins, implying a new feasible way of sensing in terahertz domain.
关键词： Fano resonance,Terahertz,Biosensor,Metasurface
更新于2025-09-23 15:21:01