Dual-band Asymmetric Transmission Research Articles

Switchable asymmetric transmission with broadband polarization conversion in vanadium dioxide-assisted terahertz metamaterials.

In this paper, we theoretically present a vanadium dioxide (VO2)-integrated metamaterial, which can achieve switchable single- and double-band asymmetric transmission (AT) in terahertz regions. When VO2 acts as a metal, the presented metamaterial device exhibits a single-band AT effect. In contrast, when VO2 transitions from the metal to the insulating state, a dual-band AT effect can be realized for the presented metamaterials. Also, it is demonstrated that there is a broadband near-perfect orthogonal polarization conversion associated with the AT effect. And the operating mechanisms are elucidated by using the Fabry-Pérot-like cavity model and the electromagnetic field distributions. Moreover, the presented nanostructure exhibits a robust tolerance for the incidence angle. Our designed metamaterial may have potential applications for switchable multi-functional devices in terahertz regimes.

A tunable dual-band asymmetric transmission metasurface with strong circular dichroism in the terahertz communication band

We propose a tunable dual-band terahertz (THz) asymmetric transmission (AT) metasurface with strong circular dichroism (CD). The structure consists of two metal layers separated by a dielectric substrate with two strips of graphene sheets attached to one side of the dielectric substrate. By changing the chemical potential of the graphene, the tunable AT and the CD can be obtained for the two bands. The transmission coefficient Tyx reduces from 0.768 to 0.34 for the first band, while it increases from 0.4 THz to 0.416 THz for the second band as the chemical potential μc increases from 0 eV to 1 eV. The CD also shows the tunable dual-band properties with peaks of 0.53 and 0.284, respectively. The coupled-mode theory is introduced to show the further physical mechanism of the tunable dual-band AT. As the dual-band AT metasurface shows strong CD, we can detect the right-handed circularly polarized (RCP) wave and left-handed circularly polarized (LCP) waves by demonstrating the field of the combination of the proposed metasurface with the mirrored one. These results would provide theoretical instructions in designing a tunable multi-band AT metasurface in the terahertz bands.

Versatile polarization manipulation in vanadium dioxide-integrated terahertz metamaterial.

Broadband and switchable versatile polarization metamaterial is crucial in the applications of imaging, sensing and communication, especially in the terahertz frequency. Here, we investigated versatile polarization manipulation in a hybrid terahertz metamaterial with bilayer rectangular rods and a complementary vanadium dioxide (VO2) layer. The VO2 phase transition enables a flexible switching from dual-band asymmetric transmission to dual-band reflective half-wave plate. The full width half maximum (FWHM) bandwidths of dual-band asymmetric transmission are 0.77 and 0.21 THz, respectively. The polarization conversion ratio (PCR) of the reflective metamaterial is over 0.9 in the frequency ranges of 1.01-1.17 THz and 1.47-1.95 THz. Angular dependences of multiple polarization properties are studied. The proposed switchable polarization metamaterial is important to the development of multifunctional polarization devices and multichannel polarization detection.

Giant dual-band asymmetric transmission based on all-dielectric metamaterial in the near-infrared band

We propose an all-dielectric metamaterial composed of bi-layered silicon structures orthogonally arranged on the sandwiched silica substrate, which exhibits giant dual-band asymmetric transmission of linearly polarized wave in the near-infrared regime, with one band working for the x-polarization and the other one for y-polarization. The dual-band AT phenomenon is explained by the distributions of electric field. In addition, the affection of the geometric parameters and incident angles to the AT parameters has been analyzed. Such an AT metamaterial has potential applications in polarization converters, switches and integrated photonic circuits.

Dual-band metasurface for broadband asymmetric transmission with high efficiency

In this paper, a dual-band asymmetric transmission metasurface for linearly polarized wave is designed, analyzed, and verified experimentally for operation in S- and C-bands. The metasurface is established by a bi-anisotropy structure with three metallic layers separated by dielectric spacers. Symmetric rectangular split-ring resonators are adopted in the top and bottom metallic layers while modified metal strip with stepped widths is utilized in the middle. Both asymmetric transmission capability and operation bandwidth are remarkably improved. According to simulation, the design yields an asymmetric transmission parameter above 0.8 within two operation bands: 2.53–2.56 and 3.80–4.71 GHz, fractional bandwidths of 1.18% and 21.39% can be deduced, respectively. The oblique incidence property is further analyzed, which demonstrates robustness response to incidence up to 50°. Two operation bands, 2.53–2.56 and 3.87–4.78 GHz, are also validated through measurement. The corresponding bandwidths 1.18% and 21.04% show tiny discrepancy related to simulated results, which validate the reliability of the design. Comparisons with other recent published results show that this structure provides relative low profile, wider operation band with high asymmetric transmission efficiency. The proposed metasurface could be applied for electromagnetic interference suppression and polarization control for modern radar and satellite communication systems and can be scaled to operate for higher frequencies with considerable bandwidth and efficiency.

Terahertz dual-band asymmetric transmission for a single cross-polarized linear wave

The reported dual-band asymmetric transmission is usually an effect of mutual polarization conversion, where one polarized wave is converted to its cross-polarization in the first band while the other polarized wave is converted to its cross-polarization in the second band. In this work, we experimentally demonstrate a dual-band asymmetric transmission effect only for one-polarized linear wave in the terahertz band. It is measured that the cross-polarization transmission coefficient Tyx reaches two peaks of 0.715 and 0.548 at the frequency of 0.74 THz and 1.22 THz, respectively. While the transmission coefficient Txy is lower than 0.2 in the wide-band from 0.5 THz to 1.5 THz. Firstly, the multiple interference model is used to discuss the physical mechanism of the dual-band asymmetric transmission. However, the second band of the calculated spectrum is offset due to the strong near field coupling between the two metal layers. The coupled-mode theory is then introduced and the fitting result of the coupled-mode theory is in good agreement with that of the experiment in the two bands. This research would provide new theoretical instructions in designing and analyzing multiband asymmetric transmission in the terahertz, microwave or the optical bands.

Dynamically adjustable and high-contrast asymmetric optical transmission based on bilateral compound metallic gratings

A dual-band asymmetric transmission (AT) device with high contrast ratio based on bilateral compound metallic gratings is proposed. The AT structure can be manufactured through connecting silver gratings on the outer surface and inner inverted T-shaped grating with an Ag film. Dual-band forward transmission arises from unidirectional surface plasmon polaritons (SPPs) excitation by the upper metallic grating when the modulated forward wave vector matches the wave vector of SPPs. The device can achieve a high transmittance of 0.67 and 0.82 with a contrast ratio of 0.997 and 0.99 at operation wavelengths 627 nm and 1238 nm, respectively. Since the SPPs coupling between two metallic structures can be used to suppress the forward transmission in specific frequency band, single-band AT function also can be realized. By adjusting those underlying parameters, the designed structure having AT capability at 624 nm and band-pass filter function at 1234 nm. The proposed structure is simple and feasible, and has great potential applications in the field of integrated optoelectronics.

Thermally switching between perfect absorber and asymmetric transmission in vanadium dioxide-assisted metamaterials.

In this paper, we propose a switchable bi-functional metamaterial device based on a hybrid gold-vanadium dioxide (VO2) nanostructure. Utilizing the property of a metal-to-insulator transition in VO2, perfect absorption and asymmetric transmission (AT) can be thermally switched for circularly polarized light in the near-infrared region. When VO2 is in the metallic state, the designed metamaterial device behaves as a chiral-selective plasmonic perfect absorber, which can result in an optical circular dichroism (CD) response with a maximum value ∼ 0.7. When VO2 is in the insulating state, the proposed metamaterial device exhibits a dual-band AT effect. The combined hybridization model and electromagnetic field distributions are presented to explain the physical mechanisms of chiral-selective perfect absorption and AT effect, respectively. The influences of structure parameters on CD response and AT effect are also discussed. Moreover, the proposed switchable bi-functional device is robust against the incident angle for obtaining perfect absorption and strong CD response as well as the AT effect. Our work may provide a promising path for the development of multifunctional optoelectronic devices, such as thermal emitters, optical modulators, CD spectroscopy, optical isolator, etc.

Dual-band asymmetric transmission based on electromagnetically induced transparency (EIT) effect in a microstrip transmission line

A dual-band asymmetric transmission device based on the nonlinear electromagnetically induced transparency (EIT) effect is presented in this paper. The device structure is composed of two P-type branches and two split ring resonators (SRRs). Dual-band EIT effect is induced based on the destructive interferences between scattering fields of the SRRs and branches in a microstrip transmission line system. Moreover, nonlinear varactor diodes and the asymmetric absorption resistor are added to EIT structure based on microstrip line couplings, which results in the asymmetric transmission property. The 10 dB and 7.5 dB transmission light contrasts at the frequencies of 0.85 GHz and 0.95 GHz with the input power of − 3 dBm are demonstrated experimentally. Such low-loss, broadband and high-contrast asymmetric transmission device results from the EIT mechanism, which possesses narrower, sharper and higher transmittance features. Such results will be very beneficial for new nonlinear electromagnetic devices.

Dual-band asymmetric optical transmission of both linearly and circularly polarized waves using bilayer coupled complementary chiral metasurface.

It is highly desirable to develop asymmetric transmission (AT) devices for both linearly and circularly polarized light. However, currently existing metamaterial-based AT devices require multi-step micro-nano fabrication processes and usually realize AT responses only for linearly or circularly polarized waves, not simultaneously for both. We here propose a dual-band AT device for both linearly and circularly polarized waves in the near-infrared region by using a bilayer coupled complementary chiral metasurface, which includes a half-gammadion-shape gold (Au) structural layer and its Babinet's complimentary copy. Unlike other multilayer AT devices working at optical frequencies, it takes less micro-nano fabrication steps. Besides, with the help of chirality and the inherent near-field coupling effect between the two complementary Au layers, the maximal AT parameters for linearly and circularly polarized waves can reach up to 0.45 and 0.56, respectively. The underlying mechanisms of dual-band AT responses are also investigated in depth from the perspectives of chirality and coupling effect. Our work offers a new and simple approach to high-performance AT devices, helps to better understand near-filed coupling effect in coupled complementary metasurfaces, and also expands their application fields.

Chiral metasurfaces formed by 3D-printed square helices: A flexible tool to manipulate wave polarization

The transmission of linearly and circularly polarized waves is studied both theoretically and experimentally for chiral metasurfaces formed by arrays of metallic square helices. The helical particles of the metasurfaces are constructed of rectangular bars manufactured by direct three-dimensional printing in solid metals. The transmittance of the metasurface is found to depend critically on the number of bars forming the square helical particles. In the case of an even number of bars, the chiral metasurface exhibits identical co-polarized transmittance of orthogonal linearly polarized waves, which are characterized by a dual-band asymmetric transmission. For an odd number of bars, the metasurface provides the same cross-polarization conversion for any polarization orientation of the incident field and thus serves as a polarization-independent twist polarizer. Finally, the transmittance of this polarizer is investigated with respect to the dimensions of the square helices. The investigated chiral metasurfaces are characterized by strong broadband circular dichroism regardless of the number of bars in the helical particles. The wide variety of transmission properties observed in the metasurfaces makes them particularly attractive for use in polarization conversion and separation devices.

Split Archimedean spiral metasurface for controllable GHz asymmetric transmission

A chiral metasurface, which obtains chirality through a subwavelength artificial structure, is essential for realizing asymmetric transmission in the application of enantioselective sensing, spin-dependent light emission, and other polarization control systems. Here, we studied a split Archimedean spiral metasurface, which can control the propagating wave from asymmetric transmission to symmetric transmission for linear polarized light. As a proof of concept, a dual-band asymmetric transmission is demonstrated in the GHz region using the coupling of the split spiral structures. The maximum asymmetric transmission parameter reaches 53%. By manipulating the height of the split spiral structures using microfluidic technology, a broadband asymmetric transmission is obtained with the bandwidth of 25.9%. Meanwhile, the asymmetric transmission can be controlled from 50% to 0%, enabling the propagation wave from asymmetric transmission to symmetric transmission. Furthermore, the asymmetric transmission is maintained when the metasurface is bent into different curvatures, promising high potential applications for optical isolation, one-way glass, and optical interconnects.

3D-printed chiral metasurface as a dichroic dual-band polarization converter.

We propose a novel design of a 3D chiral metasurface behaving as a spatial polarization converter with asymmetric transmission. The metasurface is made of a lattice of metallic one-and-a-half-pitch helical particles. The proposed metasurface exhibits a dual-band asymmetric transmission accompanied by the effect of complete polarization conversion. Regarding circularly polarized waves, the metasurface demonstrates a strong circular dichroism. A prototype of the metasurface is manufactured for the quasi-optic experiment by using a 3D printing technique utilizing a cobalt-chromium alloy, which exhibits good performances against thermal fatigue and corrosion at high temperatures.

Dual-band asymmetric transmission and circular dichroism in hybrid coupled plasmonic metamaterials

We report strong circular dichroism and asymmetric transmission of linearly and circularly polarized waves in hybrid bilayer metamaterials. In contrast to previous literatures, the bilayer metamaterials are constructed by two twisted gold complementary asymmetric nanostructures, spatially separated by a dielectric layer. Both the anisotropy and chirality contribute to asymmetric transmission and circular dichroism. The hybrid metamaterial with twisted asymmetrically split rings and apertures simultaneously exhibits strong circular dichroism and linear and circular asymmetric transmission up to 0.4. The proposed scheme can achieve strong dual-band chiroptical effects for both linearly and circularly polarized waves. The polarization conversion efficiencies and resonant frequencies can be engineered via parametric study. The hybrid metamaterial offers a route to realize multifunctional polarization devices and polarization information detections.

Microwave linear polarization rotator in a bilayered chiral metasurface based on strong asymmetric transmission

We propose and study a kind of bilayered chiral metasurface (BCM) composed of complementary L-shaped resonators with a lossless dielectric spacer that can realize linear polarization rotation with ultrahigh conversion efficiency. We present a theoretical analysis of the BCM with specific chiral geometry that enables asymmetric transmission for linear polarization only. Numerical results show that the proposed metasurface has dual-band asymmetric transmission with nearly 100% cross-polarization conversion efficiency when the loss is ignored. More importantly, depending on the incident direction, only one of the cross-polarization transmissions can approach unity while all the remaining transmissions are close to zero. As a result, nearly perfect linear polarization rotation is achieved for a particular polarization direction. We further show that the working frequency and the bandwidth of the proposed BCM can be tuned by adjusting the geometric size and spatial arrangement of the unit cell.

Broad dual-band asymmetric transmission of circular polarized waves in near-infrared communication band.

In this paper, a three-layered chiral metamaterial is proposed to achieve broad dual-band and high magnitude asymmetric transmission (AT) in near-infrared communication band for circularly polarized waves. The asymmetric parameter reaches to 0.9/0.86 at 174/235 THz, over 0.6 in broad dual bands from 160 to 183 THz and from 220 to 245 THz. Remarkably, the AT effect of circularly and linearly polarized waves can be modulated to appear or vanish with variants of the G shapes that has not been found in previous reports. The proposed structure shows great potential applications in high performance multi-band circular and linear polarizers.

Dual-band asymmetric transmission of both linearly and circularly polarized waves based on chiral meta-surface

In this paper, a chiral metamaterial structure composed of a half-gammadion and H-shape is proposed, which can realize simultaneously dual-band asymmetric transmission (AT) of both linearly and circularly polarized waves in the microwave band. Numerical simulations show that the maximum AT of linearly and circularly polarized waves can reach 0.45 and 0.36 at the resonance frequency, respectively. Specifically, compared with the previous structures, the AT amplitude of the circularly polarized wave is enhanced further. Furthermore, the physical mechanism of polarization conversion of the linearly polarized wave is analyzed by the electric field distributions and the hybridized plasmon coupling modes of the circularly polarized wave are also analyzed based on the currents densities in top and bottom metallic layers in detail. The simulated results are in good agreement with the experimental and theoretical ones for the linearly and circularly polarized waves, respectively.

Tunable dual-band asymmetric transmission for circularly polarized waves with graphene planar chiral metasurfaces.

The asymmetric transmission effect has attracted great interest due to its wide modern optical applications. In this Letter, we present the underlying theory, the design specifications, and the simulated demonstration of tunable dual-band asymmetric transmission for circularly polarized waves with a graphene planar chiral metasurface. The spectral position of the asymmetric peak is linearly dependent on the Fermi energy and can be controlled by changing the Fermi energy. The success of tunable dual-band asymmetric transmission can be attributed to the enantiomerically sensitive plasmonic excitations of the graphene metasurface. This work offers a further step in developing tunable asymmetric transmission of circularly polarized waves for applications in detectors and other polarization-sensitive electromagnetic devices.

Asymmetric transmission of linearly and circularly polarized waves in metamaterial due to symmetry-breaking

A two-dimensional chiral structure with an h-shape and H-shape on opposing sides of a dielectric layer is proposed that can realize simultaneously dual-band asymmetric transmission of linearly and circularly polarized waves in the near-infrared band. Meanwhile, the structure realizes a maximum asymmetric transmission of 0.56 and 0.30 for linearly and circularly polarized waves, respectively, at the resonant frequency. These results have been analyzed with simulations in detail. The physical mechanism of linearly and circularly polarized wave transmission and conversion based on current distribution and electric fields is also investigated.

Dual-band asymmetric transmission of chiral metamaterial based on complementary U-shaped structure

In this paper, a chiral metamaterial that consists of two complementary U-shaped structures on both sides of a substrate is proposed, which achieves dual-band asymmetric transmission effect of linearly polarized wave at 0.88 and 1.03 THz bands. The asymmetric transmission effect and resonance frequency can be adjusted through changing structure parameters. The physical mechanisms of dual-band asymmetric transmission are also analyzed based on different couple modes excited at resonant frequency.