Novel add-drop filter based on serial and parallel photonic crystal ring resonators (PCRR)

Photonic crystal ring resonators (PCRR) as momentous candidates for future photonic crystal integrated circuits (PCICs) draw worldwide attention. In this paper, different configurations are proposed based on single, parallel, and serial PCRRs. To be precise, the different coupling lengths and alignments have been discussed in double and triple PCRRs in parallel and serial configurations to achieve the highest efficiency concerning the desired applications such as an add-drop filter (ADF) and a power splitter. Moreover, in the achieved optimum double and triple PCRRs, the effect of coupling radius change has been discussed.

Design of triangular shaped slotted patch antennas for both wideband and multiband applications

In this article two fractal geometry-based slotted patch antennas are designed to achieve wideband response with multiband characteristics and reduced cross polarized radiation in both E- and H-plane for all the resonating bands. The proposed antennas are fed with microstrip line feeding formed on a FR4 substrate of size 0.25𝜆0 × 0.25𝜆0 × 0.02𝜆0 mm3 and loaded with a partial ground plane at the bottom of the substrate. HFSS is used to design and simulate both the antennas. Wideband behavior and impedance matching of Antenna-1 are improved by optimizing the factor of iteration and length of the ground plane. Due to addition of 3 identical split ring resonators (SRR) with the antenna geometry leads to achieve multiband response in Antenna-2. The dimensions of the SRR connectors and feedline have been optimized through parametric analysis to match the impedance properly at all the three resonating bands. It has been found that simulated and measurement results of both the antennas are properly matched.

Ultranarrow dual-band metamaterial perfect absorber and its sensing application

In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and high absorptivity is proposed. The MMA consists of two silver layers separated by a dielectric layer. Its top resonant element is constituted by two concentric ring resonators connected with four strips. Based on electromagnetic field simulation, the proposed MMA has two narrow absorption peaks with an absorption rate of 99.9% at 711 nm and 99.8% at 830 nm, and the corresponding line width of the two absorption peaks are only 9.7 nm and 9.8 nm. The dual-band MMA shows high absorptivity under wide incident angles. The simulated field pattern shows that dual-band perfect absorption is the combined result of the interaction of two concentric ring resonators and unit cell coupling. In addition, the hexapole plasmon mode can be observed at the outer ring at one absorption peak. The narrow plasmon resonance has a potential application in optical sensing, and can be used to measure the concentration of aqueous glucose with two frequency channels. The proposed MMA with high absorptivity is simple to manufacture, and has other potential applications, such as narrow-band filters, energy storage device, and so on.

Ultra-Thin Chiral Metasurface-Based Superoscillatory Lens

The metasurface-based superoscillatory lens has been demonstrated to be effective in finely tailoring the wavefront of light to generate focal spots beyond the diffraction limit in the far-field that is capable of improving the resolution of the imaging system. In this paper, an ultra-thin (0.055 λ0) metasurface-based superoscillatory lens (SOL) that can generate a sub-diffraction optical needle with a long focal depth is proposed, which is constructed by ultra-thin chiral unit cells containing two metal split-ring resonators (SRR) with a 90° twisted angle difference cladded on both sides of a 1.5 mm-thick dielectric substrate, with a high linear cross-polarized transmission coefficient around 0.9 and full phase control capability at 11 GHz. Full-wave simulation shows that SOL generates a sub-diffraction optical needle within 10.5–11.5 GHz. At the center frequency, the focal depth is 281 mm (10.3 λ0) within 105–386 mm, the full width at half maximum (FWHM) is 18.5 mm (0.68 λ0), about 0.7 times the diffraction limit, generally consistent with the theoretical result. The proposed ultra-thin chiral metasurface-based SOL holds great potential in integrating into practical imaging applications for its simple fabrication, high efficiency, and low-profile advantages.

Design and implementation of compact tri- and quad-band SIW power divider using modified circular complementary split-ring resonators

This paper presents a miniaturized tri- and quad-band power divider (PD)based on substrate integrated waveguide (SIW). By adopting different types of modified circular complementary split-ring resonators on the top surface of SIW, multiple passbands are generated propagating below the SIW cut-off frequency. The working principle is based on evanescent mode propagation that decreases the operating frequency of the PD and helps in the miniaturization of the proposed structure. The operating frequency of the proposed PD can be individually controlled by changing the dimensions of the resonator. To verify the proposed concept, a tri-band and a quad-band PD exhibiting 3 dB equal power division at 2.41/3.46/4.65 GHz and 2.42/3.78/4.74/5.8 GHz are designed using the full-wave simulator, validated through circuit model, fabricated and experimentally verified. The measured results agree well with the simulations. The proposed PDs have good performance in terms of reasonable insertion loss, isolation, minimum amplitude and phase imbalance, smaller footprint, easy fabrication and integration. The size of the fabricated prototype is 18.3 mm × 8.4 mm, which corresponds to 0.205λ g × 0.094λ g , λ g being the guided wavelength at the first operating frequency.

Two-Channel VO2 Memory Meta-Device for Terahertz Waves

Vanadium oxide (VO2), as one of the classical strongly correlated oxides with a reversible and sharp insulator-metal transition (IMT), enables many applications in dynamic terahertz (THz) wave control. Recently, due to the inherent phase transition hysteresis feature, VO2 has shown favorable application prospects in memory-related devices once combined with metamaterials or metasurfaces. However, to date, VO2-based memory meta-devices are usually in a single-channel read/write mode, which limits their storage capacity and speed. In this paper, we propose a reconfigurable meta-memory based on VO2, which favors a two-channel read/write mode. Our design consists of a pair of large and small split-ring resonators, and the corresponding VO2 patterns are embedded in the gap locations. By controlling the external power supply, the two operation bands can be controlled independently to achieve at least four amplitude states, including “00”, “01”, “10”, and “11”, which results in a two-channel storage function. In addition, our research may provide prospective applications in fields such as THz switching, photon storage, and THz communication systems in the future.

Bidirectional switchable beam splitter/filter based graphene loaded Si ring ‎resonators

Using bus waveguides coupled to the graphene-loaded Si-ring resonators (GSRRs) all on a Si-‎on-insulator substrate, we propose a compact bidirectional switchable beam splitter/filter ‎controlled by graphene-based electro-absorptive (refractive) mode modulation. The proposed ‎device consists of a through waveguide coupled to two drop waveguides via two GSRRs. ‎Each GSRR consists of a stack of hBN/graphene/hBN nanolayers sandwiched between two ‎Si-ring resonators. Using a finite difference time domain method, we show that the resonant ‎wavelength of GSRRs can be tuned in the range of 1551.5 < λ <1552.1 nm, linearly with the ‎slope of ~2.46 nm/eV via appropriately changing the graphene chemical potential, ‎electrostatically. The numerical results show that when both GSRRs are in an electro-refractive ‎state and a transverse electric (TE) polarized light beam of an appropriate wavelength is ‎launched into one of the though-ports, ~ 84.5% of the input intensity equally splits between ‎the adjacent drop-ports. The transmission out of the second through-port is less than 0.8%. ‎The numerical results further show that when one GSRR is in an electro-refractive mode, and ‎the other one is in an electro-absorptive state, ~68.4% of the input intensity transmits out of ‎the drop-port adjacent to the former GSRR, and the other ports experience insignificant ‎outputs (<0.7%). The device's structural symmetry makes it a bidirectional tunable, suitable for ‎long-haul optical telecommunication applications.‎