A dynamically adjustable terahertz (THz) broadband absorber based on a vanadium dioxide (VO2) hybrid metamaterial is theoretically designed. During the design, we first consider working frequency, bandwidth, excitation method and fabrication process. And then, a commercialized full wave electromagnetic (EM) calculation software CST microwave 2019 based on finite integration technology is used to simulate and optimize the performance of the device. Due to the device is excited by light, it consists of a top layer of VO2 oblique-split-ring-resonator (OSRR) array, a polyimide (PI) spacer and a bottom metal film. The simulation results show that, when the VO2 changes from insulating state to metal state under light stimulus, the absorption increases from 3% to over 90%. Meanwhile, when the VO2 is in metallic phase, the bandwidth of absorption greater than 90% reaches to 1.0 THz and the relative bandwidth is about 83%. The potential applications of the device are active EM stealth, THz wave detection and thermal imaging. This work paves a new way for simply constructing a low-cost dynamically adjustable THz broadband absorber.

A dynamically adjustable broadband terahertz absorber based on a vanadium dioxide hybrid metamaterial

Fully Optically Tunable and Flexible Composite Films for Enhanced Terahertz Control and Multifunctional Terahertz Devices

Recently, rhenium diselenide (ReSe2) has attracted considerable attention due to its high anisotropy in the layer plane, which makes it a promising candidate for wide applications in electronics and optoelectronics. In this paper, we focus on the polarization-sensitive characteristics of a large-area multilayer ReSe2 nanofilm in the terahertz (THz) region under passive and active conditions by means of THz time-domain spectroscopy. We demonstrate the passive ReSe2 nanofilm with intrinsic THz polarization anisotropy. Maximum transmittance occurs only when the polarization direction of the incident THz wave is along the Re-chains direction. More importantly, THz polarization properties of the active ReSe2 nanofilm by an external electric field applied in a selected directions are also demonstrated. The modulation depth of the THz transmission is up to 16% and the response time is on the order of picoseconds. In addition, a comparative experiment is performed on three kinds of THz polarizers, i.e., ReSe2 nanofilm, carbon nanotubes (CNTs) and wire-gird, respectively. The results prove that the performance of the polarizer based on the active ReSe2 nanofilm is comparable with those of CNTs and the THz wire-gird polarizer. Based on these studies, we believe that the polarization-sensitive ReSe2 nanofilm can find important applications in ultrafast switches, filters and modulation devices in the THz region.

https://iopscience.iop.org/article/10.1088/1361-6528/ab4377/pdf

THz polarization-sensitive characterization of a large-area multilayer rhenium diselenide nanofilm.

The 6G technology has identified the frequency range of 0.1 to 1 THz as the communication band, with a particular focus on ultrafast modulation and multi-dimensional resolution coding technology. To advance the applications of THz photonics, there is a critical need for high-performance active optoelectronic THz devices. One potential solution involves the utilization of electrically controlled semi-metallic based THz modulators, which can provide suitable modulation depth and a wide modulation bandwidth. In this research, a semi-metallic TiS2 nanofilm device was developed using femtosecond laser direct ablation. The combination of structural effects and TiS2 absorption has significantly improved active modulation. These findings indicate that TiS2-based devices are well-suited for applications in THz photonics. 

Polarization sensitive electronically tuned microgroove array THz active modulator

Broadband and large-depth THz modulation are crucially important for building next-generation THz devices in THz communication systems. Here, we present a broadband and large-depth THz modulator based on silicon/self-assembled silver nanoparticle (SAM AgNP) arrays, which exhibits a broadband modulation within the frequency range of 0.2–2.0 THz and a large modulation depth of ∼91.2% under a moderate near-infrared (NIR) light intensity of 1.77 W cm−2. For a modulation mechanism, the plasmon-enhanced NIR light absorption of SAM AgNP arrays shows a key role in increasing the photoconductivity of the device under NIR light irradiation. The experimental results are verified well by the numerical simulation. The proposed device can significantly improve the overall performance of THz systems, and opens the opportunity for designing novel nanoparticle-based THz devices.

Broadband and large-depth terahertz modulation by self-assembly monolayer silver nanoparticle arrays

We demonstrate a photo-induced high modulation depth terahertz (THz) modulator based on a VO x /Si/VO x hybrid structure. The thickness of the embedded high resistance silicon substrate is 510 µm and two layers of VO x films are 100 nm, respectively. Compared with other THz modulators based on the phase transition of vanadium oxide which were fabricated by complex chemical vapor deposition and sputtering processes, the VO x film in this device is fabricated using a simple spin coating process of VO x solution. The sample is characterized using a THz time-domain-spectroscopy system. In the test experiment, the insulator–metal-transition of the VO x is induced by two oblique incident pump lasers with a central wavelength of 650 nm from two sides. The experimental results show that it can be optically modulated in a wide frequency range from 0.2 to 2.0 THz, and the maximum modulation depth of 93% is realized when the optical power is 120 mW. Film theory and Drude theory are introduced to interpret the mechanism of modulation. This modulator has broadband, a simple fabrication process and very low optical power, which are important for broadband THz communication and all-optical THz systems.

https://iopscience.iop.org/article/10.1088/1361-6463/ab046f/pdf

Photo-induced high modulation depth terahertz modulator based on VO x ─Si─VO x hybrid structure

The invention provides a broadband terahertz wave modulation system. The system comprises a first laser transmitter, a second laser transmitter, a terahertz wave transmitter and a modulator. The firstlaser transmitter transmits a first laser beam, and the first laser beam irradiates one surface of the modulator and forms a first facula. The second laser transmitter transmits a second laser beam,and the second laser beam irradiates the other surface of the modulator and forms a second facula. The terahertz wave transmitter transmits terahertz wave, the terahertz wave is incident on one surface of the modulator and forms a third facula. The third facula and the first facula or the second facula are at least partially overlapped. According to the system, two surfaces of a sample are respectively irradiated through utilization of the two laser beams, and through photothermal effect, phase-change material vanadium dioxide is transformed from an insulated state to a metallic state, so great depth modulation of terahertz wave transmission intensity is realized. According to the system, under relatively low optical power, broadband, great depth and rapid modulation can be realized. The terahertz wave modulator prepared by the method has important application value in rapid all-optical controlled terahertz communication in the future.

Broadband terahertz wave modulator, preparation method and broadband terahertz wave modulation system

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Photo-induced high modulation depth terahertz modulator based on VO x ─Si─VO x hybrid structure

Broadband terahertz wave modulator, preparation method and broadband terahertz wave modulation system