In communication and imaging systems, anisotropic metasurfaces bring new degrees of freedom for the independent control of electromagnetic waves with different polarizations. This paper proposes a ...dual-polarization modulation metasurface (DPMM) operating in the terahertz (THz) frequency range, which can effectively and independently modulate two orthogonally linearly polarized electromagnetic waves. The metasurface unit adopts an anisotropic structure, and by integrating multiple GaN-based high electron mobility transistors (GaN-HEMTs) into the anisotropic structure, independent control of the two-dimension electron gas (2DEG) carrier concentration in the dual-polarization channel is achieved, enabling selective modulation of x -polarization and y -polarization waves. Simulation and static experimental results demonstrate the excellent modulation isolation performance of the DPMM, with a maximum isolation exceeding 45 dB. Dynamic experiments further highlight the high-speed modulation effect, with modulation speeds exceeding 1 GHz for a single channel and an overall modulation speed of 2 GHz for dual polarization, highlighting its potential for enhancing channel capacity and information throughput in THz communication and imaging systems.
As the operating frequency increases, the output power of traditional frequency doublers becomes too low to drive the next stage devices. To address this problem, a double-layer meta-chip circuit ...consisting of a symmetrical split ring (SSR) structure with a doubler circuit is presented. It combines the transmission mode in the rectangular waveguide with the resonance mode in the meta structure. The meta structure improves the coupling efficiency between the diode and electromagnetic energy, strengthens the electric field at the diode, and ultimately enhances the efficiency of the frequency doubler at low input power. From 160-180 GHz, the experiments show that the frequency doubler with SSR achieved a peak efficiency of 22.4% with an output power of 10.6 mW. Its performance of maximum output power is 45.2% better than the traditional structure, which provides an important technical approach to achieve higher efficiency at low input power.
Coding metasurfaces have drawn great attention for its digital wave manipulation in deep subwavelength-scale in the last decade, more sophisticated and flexible coding strategies suitable for ...terahertz wavefront manipulations are becoming more urgently demanded. Due to its rigidity in phase gradient division, both phase gradient metasurfaces and conventional phase coding technique lack the flexibility to expand applications in a large field of view and accurate targeting. This study presents a generalized coding method by precisely reconfiguring the array factor based on the phased array theory and metasurface concept, which can be applied for anomalous scattering and ultrafine radiation patterning. According to our quantitative analysis on the relationship between the deflected angles and the supercell spacing, a fractional coding method for arbitrary phase gradient distribution has been attained by logically discretizing the spacing scale of supercells. By switching on different coding sequences or incident frequencies, a single beam to multiple beam scanning in an expanded angular range with minimal step can be achieved on the fractional phase-coding metasurfaces. As a proof of concept, the 2-bit coding metasurfaces arranged by four fractional coding sequences have been fabricated and measured, demonstrating a consecutive single-beam steering pattern ranging from 22° to 74° in 0.34-0.5 THz. Crosswise verified by the good accordance among numerical prediction, simulation and experiment, the proposed coding strategy paves a path to delicate beam regulation for high-resolution imaging and detection.
Polarization manipulation plays a pivotal role in integrated multifunctional devices. Various metasurface-based polarization converters successfully demonstrated high efficiency and broad bandwidth. ...However, new mechanisms to aggressively enhance performance are still in dire need. Herein, theoretical and experimental evidence corroborates an efficient ultra-wideband transmissive polarization converter based on a topological design method. The triple-layer meta-device consists of a layer of anisotropic zigzag-split resonator array amid two orthogonal wire-grating layers. By splitting double zigzag lines into compound 90°V-shaped resonators, the intra-unit cross-coupling extends to strong inter-unit cross-coupling, giving birth to the multi-resonances enhancement and significant bandwidth broadening. This polarization converter can efficiently convert linearly polarized incident waves into 90° cross-polarized transmitted waves, with a conversion efficiency above 80% over 3.98-22.71 GHz, reaching a fractional bandwidth of 140.4%. The proposed meta-device enables strong cross-coupling in mutual transition from intra-unit to inter-unit. From a physical viewpoint, the novel mechanism is elucidated by the surface current and electric field distributions upon constructive interferences stemming from V-shape-resonator combinations and the Fabry-Pérot-like cavity effect. With both spectrum and function extensions, the proposed polarization conversion strategy finds essential applications in polarization-related systematic scenarios, such as 6G communication, radar imaging, anti-interference, chiral sensing, etc.
We theoretically and experimentally demonstrate a label-free terahertz biosensor with ultrahigh sensitivity and distinctive discretion. By constructing a metal-air-metal (MAM) metamaterial perfect ...absorber (MPA) with a metallic paired-ring resonator array, a hollow microfluidic channel, and a backed reflector, a novel dual-band absorptive sensing platform is proposed in the THz range. The near field coupling by dipole-induced trapped modes and the magnetic momentum caused a vertical to transverse power flux that dramatically enhanced the electromagnetic field on top of the metasurface and in the microfluidic channel, respectively. Both the resonant modes exhibit perfect absorption and produce ultrahigh normalized sensitivities of 0.47/RIU (refractive index unit, RIU) and 0.51/RIU at 0.76 THz and 1.28 THz, respectively. Compared with conventional microfluidic sensors, the salient advantages of our design are the perfect spatial overlap for light-matter interaction and polarization insensitivity. Characterized by THz time domain spectroscopic absorption quantification measurements with different concentrations of bovine serum albumin (BSA), the proposed sensor exhibits promising applications in microfluidic biosensing.
Terahertz metasurface has always aroused extensive attention for many years. However, terahertz reconfigurable metasurface is still a significant challenge. The broadband terahertz reconfigurable ...metasurface based on 1-bit asymmetric coding metamaterial is presented in this paper. The asymmetric metamaterial breaks the charge balance and provides multiple resonances, which is conducive to expanding the operating bandwidth. Conventional coding metamaterials change phase by varying the shape or size of the patch. The proposed metamaterial only disconnects or connects the metal lines in the metamaterial to obtain 1-bit phase information, which is beneficial for designing reconfigurable coding metasurface. Both simulated and experimental results show that the asymmetric metamaterial efficiently reflects the normal incident waves at 0.34–0.49 THz with a relative bandwidth of 36%, and the reflection coefficients are measured to exceeds 80%. Furthermore, the simulation and experimental results of the metasurface show that the normal incident wave is reflected as a double beam of the expected angle by configuring metamaterials with different coding sequences. This work provides important potential applications for the development of valuable dynamic terahertz beam scanning devices.
With the rapid development of terahertz (THz) application systems, on-chip integrated THz devices are in high demand. In this paper, we propose an efficient way to realize THz wave on-chip ...quasi-perfect absorption based on destructive interference between complementary meta-atom pairs. By applying a series of complementary meta-atom pairs located on the two sides of the on-chip transmission line, it is found that both electrical and magnetic induced resonances are excited simultaneously when the electromagnetic wave transmits through the line. Because of destructive interference among the resonances of the complementary meta-atom pairs, a strong absorption can be achieved. Both the experimental and simulated studies show that nearly 100% absorption can be realized within the on-chip fin line. Furthermore, greater than 90% absorption from 0.207 to 0.217 THz with a bandwidth of 10 GHz can be achieved during the experiment. Combining meta-atoms with the transmission line may provide a promising way to develop the on-chip THz devices.
Tunable focusing planar lens possesses more flexible characteristics to facilitate the expansion of its function and application. This study presents a planar meta-lens based on the phase gradient ...vanadium dioxide composite metasurface controlled by an external thermal stimulus that enables the switchable focusing. By utilizing the insulator-metal phase transition characteristics of the vanadium dioxide components, the composite metasurface can show a different phase gradient distribution that could lead to various focuses. Both simulated and experimental results demonstrate that without the external stimulus, the vanadium dioxide components display dielectric characteristics that are a phase-transparent response to THz wave. While applying an external thermal stimulus, the phase transition leads to the metallization of vanadium dioxide components that could induce the redistribution of the phase gradient of the metasurface to realize a tunable focusing. The measurements show that the results are in line with our expectations and achieve three times the tunable focal length variation from 2.5 mm with a numerical aperture (NA) of 0.78 to 7.5 mm with an NA of 0.39 at 0.65 THz, which was reversible. The proposed switchable planar metalens is expected to deliver a promising new design for electromagnetic wave dynamic manipulation and enable active applications, such as dynamic imaging or other optical systems at THz frequencies.
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