Modes Of Split Ring Resonators Research Articles

Cylindrical vector beam generator on photonic crystal cavity integrated with metal split ring nanoresonators

We propose a chip-integratable cylindrical vector (CV) beam generator by integrating six plasmonic split ring resonators (SRRs) on a planar photonic crystal (PPC) cavity. The employed PPC cavity is formed by cutting six adjacent air holes in the PPC center, which could generate a CV beam with azimuthally symmetric polarizations. By further integrating six SRRs on the structure defects of the PPC cavity, the polarizations of the CV beam could be tailored by controlling the opening angles of the SRRs, e.g., from azimuthal to radial symmetry. The mechanism is governed by the coupling between the resonance modes in SRRs and PPC cavity, which modifies the far-field radiation of the resonance mode of the PPC cavity with the SRR as the nano-antenna. The integration of SRRs also increases the coupling of the generated CV beam with the free-space optics, such as an objective lens, promising its further applications in optical communication, optical tweezer, imaging, etc.

Thermally controlled electromagnetically induced transparency in hybrid metal-InSb metamaterials at THz frequencies

We demonstrate an active controlled electromagnetically induced transparency (EIT) device via thermal control in a hybrid metamaterial, which consists of two split-ring resonators (SRRs) with integrated InSb-metal and a cut wire (CW) in a unit cell. We can dynamically control the amplitude modulation of the EIT window, by varying the temperature of the InSb thereby changing the damping rate of the dark mode of SRRs. When the temperature of the InSb changes from 240K to 320K, the EIT window undergoes modulation from on to off, and the modulation depth reaches 86.8%. The results are not only promising in designing compact slow light devices in the terahertz regime but also leading some essential applications in terahertz communications.

Ultrafast terahertz transmission/group delay switching in photoactive WSe2-functionalized metaphotonic devices

The emergence of larger-scaled two-dimensional (2D) layered materials has attracted intense research efforts and significant progress in the area of photonics and optoelectronics recently. As a remarkable representative of 2D materials, transition metal dichalcogenides (TMDCs) have demonstrated an astonishing photoconductivity and the ultrafast charge carrier dynamics, which provides excellent potentials for ultrafast optical modulators. Herein, by simply transferring a high-quality CVD-grown WSe2 multilayer on plasmon-induced transparency (PIT) metasurfaces, we demonstrate that the transmission amplitude modulation is as high as 43% and the slow light switching is up to 6 ps in the THz regime. Under photoexcitation, both functionalities are dynamically controlled within ~8 ps owing to a merit of ultrafast free carriers’ relaxation in the WSe2 multilayer. Moreover, a theoretical model consisting of two coupled harmonic oscillators and the near-field distributions are simultaneously employed to verify the strong dependence of the active PIT switching behavior on the suppression of the bright mode of split ring resonators. Our proposed versatile active WSe2-functionalized metasurface with a low cost and simple manufacturing will give researchers new insights into the ultrafast switchable metaphotonic devices.

Terahertz multiple modes defined by fractal symmetry in complementary meta-atoms

Low quality (Q) factors of the intrinsic inductive–capacitive (LC) mode as well as the parasitic dipole oscillation mode restrict high-resolution sensing using split-ring resonators (SRR). Although the trapped Fano-mode of the high-Q factor is found in asymmetric SRR, the conventional design limits the scaling down of resonators. As such, excitation and manipulation of multiple trapped modes of SRR is significant for driving innovative designs of terahertz metamaterials and metasurfaces. In this work, we present a novel approach to manipulating multiple terahertz modes by increasing the fractal levels as well as the geometric symmetry of complementary SRR. It is found that the multiple trapped modes become achievable only in the case that the gap of adjacent fractal SRR opposes each other. By increasing the fractal level, the intrinsic resonance modes change slightly, and more trapped modes appear in between the frequency range of the two major intrinsic modes. The map of surface currents and magnetic field distribution reveal that intrinsic LC resonance in the first or second level SRR dominates the intrinsic modes. By contrast, the trapped mode arises from the hybridization of high-order localized dipole oscillation as well as the multiple localized LC resonances. These findings create new design opportunities for scalable metasurfaces across the terahertz spectrum and beyond, with ability to create high-resolution sensors.

Electromagnetic near-field coupling induced polarization conversion and asymmetric transmission in plasmonic metasurfaces

In this paper, we demonstrate the effect of polarization conversion in a plasmonic metasurface structure, in which each unit cell consists of a metal bar and four metal split-ring resonators (SRRs). Such effect is attributed to the fact that the dark plasmon mode of SRRs (bar), which radiates cross-polarized component, is induced by the bright plasmon mode of bar (SRRs) due to the electromagnetic near-field coupling between bar and SRRs. We find that there are two ways to achieve a large cross-polarized component in our proposed metasurface structure. The first way is realized when the dark plasmon mode of bar (SRRs) is in resonance, while at this time the bright plasmon mode of SRRs (bar) is not at resonant state. The second way is realized when the bright plasmon mode of SRRs (bar) is resonantly excited, while the dark plasmon mode of bar (SRRs) is at nonresonant state. It is also found that the linearly polarized light can be rotated by 56.50 after propagation through the metasurface structure. Furthermore, our proposed metasurface structure exhibits an asymmetric transmission for circularly polarized light. Our findings take a further step in developing integrated metasurface-based photonics devices for polarization manipulation and modulation.

Study of photon–magnon coupling in a YIG-film split-ring resonant system

By using the stripline Microwave Vector–Network Analyser Ferromagnetic Resonance and Time Domain spectroscopy techniques, we study a strong coupling regime of magnons to microwave photons in the planar geometry of a lithographically formed split-ring resonator (SRR) loaded by a single-crystal epitaxial yttrium–iron–garnet (YIG) film. Strong anti-crossing of the photon modes of SRR and of the magnon modes of the YIG film is observed in the applied-magnetic-field resolved measurements. The coupling strength extracted from the experimental data reaches 9% at 3 GHz. Theoretically, we propose an equivalent circuit model of the SRR loaded by a magnetic film. This model follows from the results of our numerical simulations of the microwave field structure of the SRR and of the magnetisation dynamics in the YIG film driven by the microwave currents in the SRR. The results obtained with the equivalent-circuit model are in good agreement with the experiment. This model provides a simple physical explanation of the process of mode anti-crossing. Our findings are important for future applications in microwave quantum photonic devices as well as in nonlinear and magnetically tuneable metamaterials exploiting the strong coupling of magnons to microwave photons.

Fano resonances in THz metamaterials composed of continuous metallic wires and split ring resonators.

We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices.

Near-infrared active metamaterials and their applications in tunable surface-enhanced Raman scattering

By utilizing the phase change properties of vanadium dioxide (VO2), we have demonstrated the tuning of the electric and magnetic modes of split ring resonators (SRRs) simultaneously within the near IR range. The electric resonance wavelength is blue-shift about 73 nm while the magnetic resonance mode is red-shifted about 126 nm during the phase transition from insulating to metallic phases. Due to the hysteresis phenomenon of VO2 phase transition, both the electric and magnetic modes shifts are hysteretic. In addition to the frequency shift, the magnetic mode has a trend to vanish due to the fact that the metallic phase VO2 has the tendency to short the gap of SRR. We have also demonstrated the application of this active metamaterials in tunable surface-enhanced Raman scattering (SERS), for a fixed excitation laser wavelength, the Raman intensity can be altered significantly by tuning the electric mode frequency of SRR, which is accomplished by controlling the phase of VO2 with an accurate temperature control.

Enhancing infrared extinction and absorption in a monolayer graphene sheet by harvesting the electric dipolar mode of split ring resonators

Optical extinction and absorption enhancement in the infrared range of a monolayer graphene sheet by patterning split ring resonators (SRRs) is studied. It is found that the electric mode is stronger in enhancing infrared extinction and absorption compared to the magnetic mode and other higher-order modes. We improve the infrared extinction of the SRR graphene sheet by increasing the graphene area ratio in the SRR unit cell design. With the increase of the graphene area ratio, the radiation ability of the electric dipolar mode and dissipation of graphene compete for a maximum infrared absorption of about 50%. The findings on enhancing infrared extinction and absorption of the graphene sheet by harvesting the electric dipolar mode may have potential applications in terahertz and infrared detection and modulation for graphene photonics and optoelectronics.

A Compact, Planar, and CPW-Fed Metamaterial-Inspired Dual-Band Antenna

A novel compact, planar, and coplanar waveguide (CPW)-fed dual-band antenna is designed and proposed using composite metamaterial. Such composite metamaterial consists of an inner split-ring resonator (SRR) and an outer closed-ring resonator (CRR). The composite metamaterial can provide dual-band operation at 2.595-2.654 and 3.185-4.245 GHz with reflection coefficient better than -10 dB by the two resonant modes of SRR and CRR, respectively. A CPW-fed line with trapeziform ground plane and tapered impedance transformer line is employed to improve the impedance matching of the antenna. The uniqueness of this design is that the inner SRR with size much smaller than the resonant wavelength is used for obtaining the lower narrow frequency band, which makes the dual-band antenna very compact. Antenna parameters, including reflection coefficient, radiation pattern, radiation efficiency, and gain, are analyzed with numerical simulation and experimental measurement. Good agreement between the simulation and measurement is observed.

Split ring resonator sensors for infrared detection of single molecular monolayers

We report a surface enhanced molecular detection technique with zeptomole sensitivity that relies on resonant coupling of plasmonic modes of split ring resonators and infrared vibrational modes of a self-assembled monolayer of octadecanthiol molecules. Large near-field enhancements at the gap of split ring resonators allow for this resonant coupling when the molecular absorption peaks overlap spectrally with the plasmonic resonance. Electromagnetic simulations support experimental findings.

In-plane coupling and field enhancement in infrared metamaterial surfaces

In-plane coupling between the second plasmonic mode of split ring resonators and delocalized plasmons of nanowires is experimentally demonstrated from far-field measurements in metasurfaces with critical separation distances between nanostructures. Near-field calculations show that coupling drastically depends on both ``meta-atom'' shapes and separation distances. The associated field enhancement reveals these metasurfaces as good candidates for applications to sensing and surface enhanced spectroscopy.

Localised bending modes in split ring resonators

We present band diagrams for in-plane elastic waves propagating within a doubly periodic structure involving split ring resonators (SRR). From the Navier equations we derive that the lowest resonant frequencies are associated with localised bending modes solutions of a fourth-order differential equation in thin-bridges, which are responsible for the appearance of a low frequency stop band. Potential applications lie in the design of earthquake resistant systems.