Terahertz Switch Research Articles

Thermally controlled electromagnetically induced transparency metamaterial through the near-field coupling of electric and toroidal resonances

We investigate a thermally controlled electromagnetically induced transparency terahertz metamaterial through the near-field coupling of electric and toroidal resonances. The fundamental unit consists of a composite design incorporating both metal and vanadium dioxide components aimed at inducing toroidal resonance, along with a pair of metal strips generating electric resonance. Simulation results authenticate the coupling mechanism and illustrate that the envisioned EIT phenomenon can be dynamically adjusted by temperature. In a coupled oscillator model analysis, the control over coupling strength primarily emerges from the fluctuating damping rate of the bright-mode oscillator. Moreover, the displacement of the EIT peak is linked to alterations in the inherent resonant frequency of the bright-mode oscillator. This study not only broadens the potential applications for toroidal terahertz metamaterials but also enhances the range of EIT methodologies available, providing practical approaches for the utilization of terahertz slow-light devices, sensors, and switch devices.

Flexible all-optical terahertz switch based on electromagnetically induced transparent-like metamaterial

The electromagnetically induced transparent-like metamaterials have received much attention because of their excellent slow-light properties and strong nonlinear effects. They have many promising applications in novel terahertz functional devices, high-sensitivity sensors, and optical storages. In this paper, a flexible terahertz switching device based on the electromagnetically induced transparent-like effect was proposed. The device exhibited a significant slow light phenomenon without pumped laser. Meanwhile, it is demonstrated that the device has a large modulation depth and excellent tunable slow light performance with low-power pumped laser. Its amplitude modulation depth can reach 60.4% and the group delay modulation can reach 32.5 ps. And the minimum group velocity of the device in slow terahertz light can reach 0.69 × 105 m/s. Moreover, the flexible substrate of the proposed device is not easily damaged. It makes the device suited for more complex environments well. Therefore, the device will have great potential for future research on high-performance terahertz switching devices.

The terahertz isolator and switch based on the nonreciprocal feature of magnetized InSb layered photonic structure

In this paper, a multifunctional device based on a one-dimensional (1-D) magnetized InSb layered photonic structure (LPS) that can achieve the function of a magnetic-controlled isolator and switch is proposed, with the advantages of multi-function. The external conditions for realizing the LPS function are temperature 303 K, magnetic field B1 = 0–0.3 T, B2 = 0 T, which are easier to obtain through an applied magnetic field device. B1 and B2 differ only in intensity. Both B1 and B2 are applied magnetic fields parallel to the positive y-axis. The change of magnetic field can influence the the cyclotron frequency of the electron which affect the dielectric constant of the tensor form, and finally lead to the change of refractive index (RI), resulting in interesting electromagnetic phenomena. Temporal inversion symmetry and spatial inversion symmetry could be easily broken to actualize nonreciprocal phenomena because of the magneto-optic effect of Indium antimonide (InSb) and an asymmetric arrangement of quasi-periodic media. For the isolator, the transmittance of forwarding propagation arrives at 0.994 and the backward scale is much closer to 0. The isolation and insertion loss achieves 34 dB and 0.0269 dB, and the range of the angle stabilization is from 17° to 31°. For the switch operating, just changing the value of B1 from 0.3 T to 0 T, can realize the function of the switch operating instead of an isolator. This shift is easier to reach by turning off the magnetic field. The extinction ratio attains 99.8 % and angle stabilization is between 9° and 31°. This magnetic-structure multifunctional LPS can play a vital constructive role in medicine, computing, and other fields.

Terahertz graphene-based multi-functional anisotropic metamaterial and its equivalent circuit model

In this paper, a graphene-based multi-functional anisotropic metamaterial composed of two finite parallel graphene ribbons in each unit cell is designed and proposed in the 0.1–5.5 terahertz (THz) region. Simulations are performed by the finite element method (FEM) in the frequency-domain solver of CST Software. An equivalent circuit modeling (ECM) as a simplified approach has been provided by a MATLAB code to model the performance of the metamaterial. The metastructure is polarization-sensitive because of the geometric non-symmetry. The absorption/reflection spectrum of the metamaterial is dynamically tunable by changing the Fermi energy level of the graphene. The introduced metamaterial can act as a THz switch and inverter at 1.23 and 4.21 THz. It acts as an ON state when the incident electric field is in the x-direction and acts as an OFF state when the incident electric field is in the y-direction. It can also act as a bi-functional mirror: a triple-band mirror for the incident electric field in the x-direction and an ultra-broadband mirror for the incident electric field in the y-direction. The proposed metamaterial has a maximum absorption of 100%, maximum linear dichroism (LD) of 100%, and a maximum switching extinction ratio of 33.01 dB. The metamaterial and its applications could be used as a potential platform in future THz devices and systems.

Tunable multistate terahertz switch based on multilayered graphene metamaterial

We proposed plasmonic effect-based narrow band tunable terahertz switches consisting of multilayered graphene metamaterial. Though several terahertz optical switches based on metamaterials were previously reported, these switches had complicated fabrication processes, limited tunability, and low modulation depths. We designed and simulated ingenious four- and eight-state terahertz optical switch designs that can be functional for multimode communication or imaging using the finite-difference time-domain simulation technique. The plasmonic bright modes and transparency regions of these structures were adjusted by varying the chemical potential of patterned graphene layers via applying voltage in different layers. The structures exhibited high modulation depth and modulation degree of frequency, low insertion loss, high spectral contrast ratio, narrow bandwidth, and high polarization sensitivity. Moreover, our proposed simple fabrication process will make these structures more feasible compared to previously reported terahertz switches. The calculated modulation depths were 98.81% and 98.71%, and the maximum modulation degree of frequencies were $$\sim$$ 61% and $$\sim$$ 29.1% for four- and eight-state terahertz switches, respectively. The maximum transmittance in transparency regions between bright modes and the spectral contrast ratio were enumerated to be 95.9% and $$\sim$$ 96%, respectively. The maximum insertion losses were quite low with values of 0.22 dB and 0.33 dB for four- and eight-state terahertz switches, respectively. Our findings will be beneficial in the development of ultra-thin graphene-based multistate photonic devices for digital switching and sensing in the terahertz regime.

Polarization-sensitive tunable extraordinary terahertz transmission based on a hybrid metal-vanadium dioxide metasurface.

Thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO2) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops, while the loops are connected with strips of VO2. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of VO2. For a y-polarized incident field, the resonance transmission peak redshifts from 0.88 to 0.81 THz upon insulator-to-metallic phase transition of VO2. For an x-polarized incident field, the transmission resonance at 0.81 THz is observed in the insulator phase. However, in the metallic phase of VO2, the electromagnetic field is effectively reflected in the 0.5-1.1 THz range with a transmission level lower than 0.14. The proposed metasurface can be utilized as a terahertz modulator, reconfigurable filter, or switch.

Terahertz mode switching of spin reflection and vortex beams based on graphene metasurfaces

Gradient metasurface provides a new way for controlling electromagnetic wave, and vortex beam can be widely used to improve the performance of wireless communication. Here, graphene-based metasurfaces are proposed for mode switching, which can dynamically adjust the wavefront of circularly polarized wave in terahertz band. The designed meta-atom is composed of quasi-I-shaped metal structure, graphene layer, spacer, and metal substrate. 360° phase cover is realized by rotating the top metal structure. Two examples are presented to demonstrate mode switching of metasurface, namely gradient metasurface and vortex beam generator. By setting Fermi energy level of graphene as 0.015 eV and 0.70 eV, the designed gradient metasurface realizes the switching between anomalous reflection and mirror reflection for left-handed/right-handed circular polarization based on Pancharatnam-Berry phase theory at 1.2 THz. Then, mode number of orbital angular momentum generated by vortex beam generator can be reconstructed by changing Fermi energy level. The proposed scheme could be applied in many fields, such as terahertz switch and wireless communication.

Terahertz meta-chip switch based on C-ring coupling

Abstract Terahertz switch is one of the key components of future communication, radar, and imaging systems. Limited by the strong electromagnetic coupling in subwavelength scale, the traditional terahertz switch is difficult to meet the increasing application requirements. In this paper, a parallel topology terahertz meta-chip switch based on the combination of equivalent circuit theory and electromagnetic coupling is proposed. The meta-chip is realized by adjusting the density of two-dimensional electron gas of InP-HEMT, which converts the electromagnetic coupling between the microstructure and microstrips. By using the 90 nm gate length InP-HEMT process, a C-ring loaded meta-chip is fabricated and tested in this paper. The results show an insertion loss lower than 1 dB with a 10 dB switching ratio, which is 20% higher than that without C-ring while ensuring the rather low insertion loss. It shows that the presented mechanism has positive significance for the design of terahertz band functional devices.

Broadband tunable perfect absorber with high absorptivity based on double layer graphene

Due to the problems of low absorptivity and the narrow bandwidth of existing broadband absorbers, a perfect broadband tunable absorber with high absorptivity based on double-layer graphene is proposed in this study with 99% high absorptivity as the reference standard, and its theoretical analysis is performed. The designed absorber consists of complete graphene, upper dielectric material, patterned graphene, lower dielectric material and the gold substrate. Through numerical calculation, the designed absorbing structure can achieve high absorption rate of more than 99% in the range of 2.54–3.70 THz, and has a continuous bandwidth of 1.16 THz. In addition, the absorption range is 52%–100% by changing the Fermi level of the graphene layer. The perfect absorber is symmetrical in rotation center and insensitive to incident angle and polarization. It can be widely used in terahertz switch, modulator design, power acquisition and other related fields.

Ultrafast all-optical metamaterial terahertz switch by exploiting nanoparticle-enriched substrate nonlinearity and graphene resonators

The emergence of graphene as a new material with several extraordinary optical properties paves a way to introduce new electromagnetic devices in the terahertz (THz) band. In this paper, we have exploited the unique qualities of graphene in combination with the optical Kerr effect in order to propose a new THz switch. In the proposed structure, two graphene layers with circular and notch ring patterns are stacked to obtain two narrowband absorption peaks at the frequencies of 3.65 and 6.5 THz with high absorption values of 92% and 97%, respectively. The imposed pump power in interaction with the nanocomposite substrate provides a controlling mechanism that makes this structure an ideal candidate for all-optical devices in the THz regime. The obtained switching time of the proposed structure is 2 ps, and the maximum extinction ratio of 83% is achieved for the pump power of 273 mW. Moreover, the absorption spectrum of the switch can be manipulated by the chemical potential of graphene layers, which is useful for electro-optical modulation application. The application of the THz switch as an all-optical tunable filter is also studied in this paper.

Electrically tunable terahertz switch based on superconducting subwavelength hole arrays.

We experimentally demonstrate an electrically tunable superconducting device capable of switching the extraordinary terahertz (THz) transmission. The planar device consists of subwavelength hole arrays with real-time control capability. The maximum transmission coefficient at 0.33 THz is 0.98 and decreases to 0.17 when the applied voltage only increases to 1.3 V. A relative intensity modulation of 82.7% is observed, making this device an efficient THz switch. Additionally, this device exhibits good narrow-bandpass characteristics within 2 THz, which can be used as a frequency-selective component. This study offers an ideal tuning method and delivers a promising approach for designing active and miniaturized devices in THz cryogenic systems.

Switchable bifunctional metamaterial for terahertz anomalous reflection and broadband absorption

A terahertz switchable metamaterial is proposed with bifunctional properties based on a mixed structure of graphene and vanadium dioxide (VO2). When VO2 is metal, this metamaterial can be used to perform the function of anomalous reflection. It is composed of VO2 blocks, topas spacer, and VO2 film. By adjusting the size of VO2 blocks, the gradient transformation is formed, so the normally incident beam is reflected to the left side at the angle of 38.4° at 3.0 THz. When VO2 is insulator, this design can be used to realize a broadband absorber. It has a broadband absorption with more than 90% absorptance in the range of 1.29–3.08 THz, and there are two absorption peaks with 99% absorptance at 1.545 THz and 2.55 THz. By adjusting Fermi energy level of graphene, intensity and bandwidth of broadband absorption can be dynamically changed. In addition, the designed metamaterial is insensitive to incident angle. Our design could be applied in many promising fields as intelligent absorption and terahertz switch.

Switchable terahertz metamaterial absorber with broadband absorption and multiband absorption.

Based on the phase-transition property of vanadium dioxide (VO2), a terahertz bifunctional absorber is proposed with switchable functionalities of broadband absorption and multiband absorption. When VO2 is metal, the system is regarded as a broadband absorber, which is composed of VO2 patch, topas spacer, and VO2 film with metallic disks inserted. The system obtains a broadband absorption with absorptance >90% from 3.25 THz to 7.08 THz. Moreover, the designed broadband absorber has a stable performance within the incident angle range of 50°. When VO2 is dielectric, multiband absorption with six peaks is realized in the designed system. Graphene and the metallic disk-shaped array play the dominant role in the mechanism of multiband absorption. Through changing the Fermi energy level of graphene, the performance of multiband absorption can be dynamically adjusted. Because of the switchable functionalities, the proposed design may have potential application in the fields of intelligent absorption and terahertz switch.

Multifunctional and dynamically tunable terahertz metamaterials based on TiNi shape memory alloy films with a simple design

In the terahertz (THz) fields, a crucial point of restricting its development and application is the lack of dynamic and multifunctional materials. In this work, NiTi films are innovatively introduced into the design, and multifunctional and dynamically tunable terahertz metamaterials are proposed. The influence and mechanism of the shape deformation and conductivity changes before and after martensitic transformation on the electromagnetic response are systematically investigated and revealed. Based on the novel NiTi metamaterials, inductance-capacitance (LC) resonance and dipole resonance are used simultaneously for the terahertz filter, and an excellent dual-band filter is obtained. The frequencies of both LC and dipolar resonances can be dynamically tuned to the desired operating frequencies by driving the martensitic transformation. And the resonant frequency of the band-stop filter achieves a dynamic modulation range up to 0.56 THz. Furthermore, the results also show that when martensitic transformation occurs, the terahertz wave transmission can be tuned from 0.78 to 0.04 at 0.47 THz. Moreover, as an excellent switch, the ON state transmittance is one order of magnitude higher than the OFF-state transmittance. In brief, this study provides a new perspective and ideas for developing a tunable dual-band terahertz filter and thermal-induced terahertz switch.

Switchable Fano Resonance Based on Cut-Induced Asymmetric Split-Ring Resonators with Dirac Semimetal Film

We present cut-induced asymmetric split-ring resonator (CASRR) structure that can achieve switchable Fano resonance based on Dirac semimetals at the terahertz region. By changing the asymmetric geometric parameter from 3 to 13 µm, the transmission spectrum can be switched from single to dual channel and the Fano resonance can be gradually enhanced, which is consistent with the two coupled oscillators model. Meanwhile, the Fano effect can also be effectively switched by adjusting the Fermi energy of Dirac semimetal film (DSF) and it is suitable for practical applications. In the view of sensing application, the sensitivity based on Fano resonance is up to 69.75 GHz/RIU and 134.25 GHz/RIU with the thickness of sample 1 μm and 20 μm, respectively. Such manipulation of Fano resonance by using DSF may have potential applications in terahertz switch, sensor, and multichannel communication.

Reconfigurable terahertz switch using flexible L-shaped metamaterial.

The design of a reconfigurable terahertz (THz) switch by using flexible L-shaped metamaterial (FLM), which is composed of dual-layer L-shaped metamaterials on polydimethylsiloxane substrate, which has three resonances at 0.57, 1.05, and 1.52 THz, is presented. By stretching the FLM along the x-axis direction, the transmission intensity is increased gradually at the transverse electric mode (TE) and reduced at the transverse magnetic (TM) mode, respectively. Reversely, by stretching the FLM along the y-axis direction, the transmission intensity is reduced gradually at the TE mode and increased at the TM mode, respectively. These electromagnetic responses of FLM provide the optical-logic behaviors with programmable characteristics by stretching FLM at different polarized light. It indicates that the proposed FLM could be used for the dual/triple-band switching, polarization switching, and programmable switching applications.

Bistable Terahertz Switch Designed by Integration of a Graphene Plasmonic Crystal into Fabry-Perot Resonator

An appropriately designed periodic lattice in graphene can cause plasmonic modes, absorbing a specific THz frequency band, minimizing transmission. A suitable Fabry-Perot cavity, on the other hand, can resonate at another desired frequency in the nearby THz band, enhancing the transmittance. Integrating, these two types of structures into a THz switch, in which the peaks of the plasmonic absorption and the Fabry-Perot resonance band play the role of the OFF and ON states, yielding a bistable switch with a very high output due to the resonance and a high extinction (ON/OFF) ratio. By placing a patterned with an array of circular micro-holes with a plasmonic absorption band centered about 4.1 THz in the middle of a Fabry-Perot vertical cavity of resonance band centered about 3.9 THz, we have designed a bistable THz switch with 87% transmission in the ON state and the extinction ratio of 23 dB. The optical bistability, in this switch, is the consequence of graphene nonlinear property invoked by the enhanced optical intensity due to the cavity resonance, adding an intensity-dependent term to the graphene surface conductivity.

Manipulation terahertz wave with electro-rheological fluid

Diverse applications of terahertz technology depend on the efficient manipulation of terahertz beam. Terahertz switch with transmitting electromagnetic intensity tunability is essential for effective control of terahertz wave. Existing approaches are a lack of simple structure able to achieve superior switching performance. Here we experimentally demonstrate a new approach to manipulate terahertz wave transmittance controlled by Calcium and Titanium Precipitate (CTP) electro-rheological (ER) fluid, and develop a novel CTP ER-fluid switch at terahertz frequencies based on this mechanism. In this way, we achieve perfect terahertz wave intensity switching through actively adjusting the external applied electric field. This operating principle ensures that our presented device can operate in terahertz frequency range.

Symmetry-broken silicon disk array as an efficient terahertz switch working with ultra-low optical pump power**Project supported by the National Key R&D Program of China (Grant No. 2017YFA0701005) and the National Natural Science Foundation of China (Grant Nos. 11974221, 91750201, 61927813, and 61775229). Z. Han also acknowledges the support from the Taishan Scholar Program of Shandong Province, China (Grant No. tsqn201909079)

The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components, among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity. To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium. However, these reported terahertz switches usually suffer from an inferior performance, e.g., requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances. In this paper, we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations. This resonance, which can never be excited for regular circular Si disks, can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band. Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%, the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator (SRR) based terahertz switch reported in the literature.

Terahertz Switch Utilizing Inorganic Perovskite-Embedded Metasurface

Various applications of terahertz technology require a large number of various terahertz wave control devices. Yet, high efficient and rapid-response terahertz switch is still a great challenge. Here, we introduce a new scheme, based on inorganic perovskite quantum dots (CsPbBr3-QDs) embedded metasurface under different pump laser powers realize terahertz wave high-speed switching performance. The off-on speed of the presented device achieves to be 8MHz. This kind of components provides a new idea and a cost-effective functional solution for manipulating the terahertz waves in emerging terahertz devices and systems.