Electromagnetic force based on trapped mode of asymmetrical split ring

In this paper, a multi-layered structure based on coupled magnetic/electric resonators is presented. The multi-layered structure can generate a significant electromagnetic force in the terahertz band. The electromagnetic force is calculated by using Maxwell Stress Tensor. The asymmetrical split ring is utilized for field confinement and the multi-layered structure enhances the coupling in the dielectric layer and in the air gap. This leads to a high Q factor and large electromagnetic force. By taking the gravity and the area of the unit cell into consideration, we prove that this force is large enough (about three orders of magnitude higher than in the visible band) to manipulate the unit cell with a small incident power density (<50 nW/μm²).     

Tunable dual-band infrared chiral metamaterials based on double-layered asymmetric U-shape split ring resonators

We have numerically demonstrated chiral metamaterials based on double-layered asymmetric U-shape split ring resonators. Dual-band circular dichroism is found in the whole frequency regime from 50 to 250 THz by studying the transmission properties. Huge optical activity and the induced negative refractive index are obtained at resonance by calculating the optical activity and ellipticity of the transmitted E-fields. Chirality parameter and effective refractive index are retrieved to illustrate the tunable optical properties of the metamaterials. The underlying mechanisms for the observed circular dichroism are analyzed. These metamaterials would offer flexible electromagnetic applications in the infrared regime.     

Screw split ring resonator as building block of three-dimensional chiral metamaterials

We proposed and numerically investigated the influence of spatial topology on the infrared frequency region response of chiral metamaterials based on discrete deformed split ring resonators. Compared with the well studied continuous helix, the proposed metamaterials with discrete topology exhibit broad band chiral electromagnetic response. It is shown that the conversion between left and right circular polarization waves for our model is much broader than the continuous helix model. The observed cross-coupling between electric and magnetic fields results from the chiral electric currents on the resonators due to the broken mirror symmetry. The findings are useful for the design of future real three-dimensional chiral metamaterials with tunable optical response.     

A dual-band polarization insensitive metamaterial absorber with split ring resonator

A dual-band polarization insensitive absorber has been proposed . Unlike the previous dual band absorber composed of composite structures, only one square metal ring with a slit at the middle of each side can be used to achieve the dual-band absorption. The calculated results show two distinct absorption peaks of 0.96 at 10 GHz and 0.99 at 20 GHz. In addition, the positions of the two peaks are strongly influenced by the width of the slit (g). More importantly, the absorptions of the two peaks keep higher than 0.9 while g changing. The dual-band absorber may have many potential applications in scientific and technological areas because of its excellent absorption characteristics and concise structure.     

Spin polarization direction switch based on an asymmetrical quantum wire

A scheme for a spin polarization direction switch is investigated by studying the spin-dependent electron transport of an asymmetrical quantum wire with Rashba spin–orbit coupling. It is found that the spin polarization direction can be switched by changing the direction of the external current. The physical mechanism of this device arises from the fact that the symmetries in the longitudinal and transverse directions are all broken but _C2$C_2$-rotation and time-reversal symmetries are still preserved. Further studies show that the spin polarization is robust against disorder, displaying the feasibility of the proposed structure for a potential application.     

Ultrashort broadband polarization beam splitter based on an asymmetrical directional coupler

An ultrashort polarization beam splitter (PBS) based on an asymmetrical directional coupler is proposed by utilizing the evanescent coupling between a strip-nanowire and a nanoslot waveguide. In order to be convenient for integration with other components, mode converters between the nanoslot waveguide and the strip-nanowire are introduced and merged into S-bends to achieve an ultracompact PBS. As an example a 6.9 μm long PBS based on a silicon-on-insulator platform is designed, and the length of the coupling region is as small as 1.3 μm. Numerical simulations show that the present PBS has a very broad band (>160 nm) for an extinction ratio of >10 dB.     

Magnetic response of split ring resonator metamaterials: From effective medium dispersion to photonic band gaps

On systematically investigating the electromagnetic response of periodic split-ring resonator (SRR) metamaterials as a function of the size-to-wavelength (a/λ) ratio, we find that the stop bands due to the geometric resonances of the SRR weaken with increasing (a/λ) ratio, and are eventually replaced by stop bands due to Bragg scattering. Our study traces the behaviour of SRR-based metamaterials as the resonance frequency increases and the wavelength of the radiation finally becomes comparable to the size of the unit cell of the metamaterial. In the intermediate stages, the dispersion of the SRR metamaterial can still be described as due to a localized magnetic resonances while Bragg scattering finally becomes the dominant phenomenon as a/λ∼1/2.     

Asymmetric chiral metamaterial circular polarizer based on four U-shaped split ring resonators

An asymmetric chiral metamaterial structure is constructed by using four double-layered U-shaped split ring resonators, which are each rotated by 90° with respect to their neighbors. The peculiarity of the suggested design is that the sizes of the electrically and magnetically excited rings are different, which allows for equalizing the orthogonal components of the electric field at the output interface with a 90° phase difference when the periodic structure is illuminated by an x-polarized wave. As a result, left-hand circular polarization and right-hand circular polarization are obtained in transmission at 5.1 GHz and 6.4 GHz, respectively. The experiment results are in good agreement with the numerical results.     

Design and implementation of dual-band antennas based on a complementary split ring resonators

A simple dual-band antenna design and implementation method is proposed in this work, based on the equivalent media properties inspired by resonant metamaterial elements. The equivalent circuit model of dual-band patch antennas based on a complementary split ring resonator (CSRR) is presented and validated. The dual-band patch antenna is designed etching a CSRR in the patch of a conventional rectangular microstrip patch antenna. The first resonance is governed by the quasi-static resonance of the CSRR while the second resonance is originated by the rectangular patch. The fact of etching a CSRR on a rectangular patch antenna also produces a miniaturization of a conventional patch antenna. The equivalent circuit model proposed in this letter is sound in order to understand the functionality of dual-band patch antennas based on a CSRR. Good agreement between simulation, equivalent circuit model and experimental results is shown and discussed. These results lead the equivalent circuit model to become a simple and straightforward tool for the design of this type of multiband antennas, of low cost and versatile operation for a broad range of wireless communication systems.     

Microstrip notch filters based on open interconnected split ring resonators (OISRRs)

Two kinds of inorganic/organic hybrid junctions based on ZnO nanorods (NRs), i.e. two-layer planar heterojunction and embedded bulk composite structures, were fabricated on ITO glass substrates. Surface photovoltage (SPV) methods based on a Kelvin probe and a lock-in amplifier were respectively utilized to study the photogenerated charges at the surface and the interface in the ZnO-based hybrid junctions. Results indicate that the lock-in SPV response of the bulk composite structure is much higher than its planar counterpart in terms of intensity and spectral range. Therefore, ZnO NR/PF (poly(9,9-di-n-octylfluorenyl-2,7-diyl)) embedded bulk composite structures are more suitable and preferred for photovoltaic application.     

Wide-range optical sensors based on a single ring resonator with polarization multiplexing

Wide-range optical sensors based on a single ring resonator are investigated theoretically and experimentally.The sensor worked at the TE and TM modes simultaneously. Because the sensitivities of the TE mode and TM mode are different, the TE mode is used for the large measurement range, and the TM mode is used for the high sensitivity measurement. The experimental results showed that the measurement range for the TE mode was almost three times larger than that of the TM mode. A sensitivity of 233 nm/RIU was achieved for the wavelength interrogation of the TM mode.     

Focusing microwaves into subwavelength dimensions with a half-cylindrical hyperlens based on split ring resonators

Hyperlenses based on metamaterials can be applied to subwavelength imaging in the lightwave band.In this letter,we demonstrate both through simulations and experimentally verified results that our proposed halfcylindrical shaped hyperlens can be used for super-resolution microwave focusing in a TE mode.Based on split ring resonators,the hyperlens satisfies a hyperbolic dispersion relationship.Simulations demonstrate that the focused spot size and position are insensitive to the rotation angle of the hyperlens around its geometric center.Experimental results show that a focused spot size 1/3 of the vacuum wavelength is achieved in the microwave band.     

Tunable THz wave absorption by graphene-assisted plasmonic metasurfaces based on metallic split ring resonators

Journal of Nanoparticle Research - La(Ni0.75W0.25)O3 perovskite oxide was prepared via the sol–gel Pechini route. The pure crystalline phase was verified via X-ray diffraction measurements...     

Waveband switchable multi-wavelength erbium-doped fiber ring laser based on wavelength-dependent polarization rotation mechanism

A waveband switchable multi-wavelength erbium-doped fiber ring laser based on wavelength-dependent polarization rotation mechanism and birefringence-based in-line comb filter is proposed and demonstrated. The two lasing wavebands, around 1530 and 1560 nm region, can be efficiently switched by simply rotating the polarization controllers (PCs). The channel spacing is 0.4 nm which was determined by the length of polarization maintain fiber (PMF) used in the experiment. The experimental results show that the waveband switchable is an intrinsic feature of multi-wavelength fiber ring lasers by incorporating a passive polarizer in the laser cavity.     

Wide-band tunable passively Q-switched all-fiber ring laser based on nonlinear polarization rotation technique

A wide-band tunable passively Q-switched all-fiber ring laser based on nonlinear polarization rotation (NPR) technique is demonstrated. The NPR-induced intensity-dependent loss effect acts as an artificial saturable absorber, which was used to achieve the Q-switched operation with a low pump threshold of about 25 mW. Taking advantage of the intracavity birefringence-induced spectral filtering effect, the central wavelength of Q-switched pulse can be continuously tuned from 1543.4 to 1592.4 nm by simply rotating the PCs.     

Tunable mid-infrared absorber based on Dirac metamaterials

In this paper, a tunable metamaterial absorber based on a Dirac semimetal is proposed. It consists of three different structures, from top to bottom, namely a double semicircular Dirac semimetal resonator, a silicon dioxide substrate and a continuous vanadium dioxide（VO₂） reflector layer.When the Fermi energy level of the Dirac semimetal is 10 meV, the absorber absorbs more than 90% in the 39.06–84.76 THz range. Firstly, taking advantage of the tunability of the conductivity of the Dirac semimetal, dynamic tuning of the absorption frequency can be achieved by changing the Fermi energy level of the Dirac semimetal without the need to optimise the geometry and remanufacture the structure. Secondly, the structure has been improved by the addition of the phase change material VO₂, resulting in a much higher absorption performance of the absorber. Since VO₂ is a temperature-sensitive metal oxide with an insulating phase below the phase transition temperature（about 68 ℃） and a metallic phase above the phase transition temperature, this paper also analyses the effect of VO₂ on the absorptive performance at different temperatures, with the aim of further improving absorber performance.     

Progress on CRLH metamaterials based on dielectric resonators

Combination of magnetically-resonant dielectric resonators and TE cut-off waveguide structures provides unbalanced or balanced composite right/left handed transmission lines. This idea has been expanded into 1-D, 2-D, and 3-D composite structures, and can be applied to potential microwave and millimeter wave circuits and antennas in the same manner as conventional composite right/left handed transmission lines.     

Stable single longitudinal mode fiber ring laser based on polarization maintaining erbium doped fiber

A stable single longitudinal mode (SLM) fiber ring laser that incorporates polarization maintaining erbium doped fiber (PM EDF) acting as gain medium and saturable absorber is proposed and demonstrated. Both theoretical deviation and experimental result prove that optical intensity is time invariant when the laser operates in single longitudinal mode, the SLM operation can be approximately verified by optical intensity analysis, which is practical to analyze longitudinal mode in the application of engineering. The linewidth of the fiber ring laser is measured by the delayed self-heterodyne interferometery, and an acousto-optic frequency shifter is employed to shift the lasing frequency and eliminate zero frequency interfere. The SLM operation is verified by the scanning Fabry–Perot interferometer, whereas the lasing frequency drift slowly during a period of 2 h, PM EDF is proved to be effective on suppressing mode hopping and selecting longitudinal mode.     

Microwave permeability of metamaterials based on ferromagnetic composites

In this paper, we focus on metamaterials based on ferromagnetic composite combined with an inductive pattern. CoFeSiB amorphous ferromagnetic glass-coated microwires and thin films are involved in the composite. The inductive pattern is a coiling of Copper wire with a varying number of loops. We derived the microwave permeability of the ferromagnetic material inside the inductive pattern through a Landau–Gilbert model of gyromagnetism. In agreement with experimental results, the engineering of resonance frequency of the sample is achieved through the number of loops of the coiling.     

Arbitrary angle waveguide bends based on zero-index metamaterials

In this paper, efficient arbitrary angle bends based on impedance-matched zero-index metamaterials (ZIMs) are proposed. Numerical simulations on ZIM-based bends are carried out in waveguide systems. The results show clearly that electromagnetic waves can tunnel through the ZIM-based bends with high transmittance at any bending angles. Moreover, a realistic ZIM-based bends are designed and fabricated on microstrip transmission line. Both simulated and experimental results confirm well the low loss and arbitrary angle bending effects in a system hiring ZIM-based microstrip ring resonator as bending corners.