Mingzhuo Zhao

Tunable ultra-wide band-stop filter based on single-stub plasmonic-waveguide system

A nanoscale plasmonic filter based on a single-stub coupled metal–dielectric–metal waveguide system is investigated theoretically and numerically. A tunable wide band-stop can be achieved by loading a metal bar into the stub. The band-stop originates from the direct coupling between the resonance modes. The bandwidth and the center wavelength of the band-stop can be tuned by changing the parameters of the metal bar. Compared with previously reported filters, the plasmonic system has the advantages of easy fabrication and compactness. Our results indicate that the proposed system has potential to be utilized in integrated optical circuits and tunable filters.

Dual tunable plasmon-induced transparency based on silicon–air grating coupled graphene structure in terahertz metamaterial

A graphene plasmonic structure consists of three graphene layers mingled with a silicon-air grating is proposed. We theoretically predict and numerically simulate the plasmon-induced transparency effect in this system at terahertz wavelengths, and a dual plasmon-induced transparency peaks can be successfully tuned by virtually shifting the desired Fermi energy on graphene layers. We investigate the surface plasmon dispersion relation by means of analytic calculations, and we can achieve the numerical solution of propagation constant got by the dispersion relation. A suitable theoretical model is established to study spectral features in the plasmonic graphene system, and the theoretical results agree well with the simulations. The proposed model and findings may provide guidance for fundamental research of highly tunable optoelectronic devices.

Keeping Good Sensing Performance of Metal–Dielectric–Metal Waveguides After Coating Treatment

Good sensing performance is observed in metal–dielectric–metal (MDM) waveguides in recent research. However, Ag will be oxidized in air. The oxidization layer makes the sensing performance not as high as before. Plating an SiO2 film on the surface of the Ag waveguide not only can avoid oxidization but can keep good sensing performance through our numerical discussion as well. The decaying rate of electric field E at the interface and inside is also defined to illustrate the phenomenon mentioned above. We hope our findings will provide guidance for the integrated plasmonic devices.

Filtering Property Based on Ultra-Wide Stopband in Double Sector/Sectorial-Ring Stub Resonator Coupled to Plasmonic Waveguide

A double sector or sectorial-ring stub resonator coupled to a plasmonic waveguide is proposed and investigated. This resonator is built with two same stubs that are symmetrically arranged together, which has the advantages of realizing asymmetrical single stub and forming no-distance double stub. The characteristic spectral responses of the two novel systems are simulated by using the finite-difference time-domain method. The results show that an ultra-wide stopband is achieved, and a multiple double stub is realized by altering the structure size of the double stub that plays important role in the stopband phenomenon. A tunable stopband, a specific filtering waveband and an optimum structural parameter are obtained by adjusting the inner radius (r), (outer) radius (R), or central angle (θ) of the double stub. The wavelength and bandwidth of the stopband have various variations with the changing of r, R, or θ, and the stopbands in the two systems have similar changes and different features. This paper provides a promising application for band-stop nanofilters and plasmonic integrated optical circuits.

Novel oscillator model with damping factor for plasmon induced transparency in waveguide systems

We introduce a novel two-oscillator model with damping factor to describe the plasmon induced transparency (PIT) in a bright-dark model plasmonic waveguide system. The damping factor γ in the model can be calculated from metal conductor damping factor γc and dielectric damping factor γd. We investigate the influence of geometry parameters and damping factor γ on transmission spectra as well as slow-light effects in the plasmonic waveguide system. We can find an obvious PIT phenomenon and realize a considerable slow-light effect in the double-cavities system. This work may provide guidance for optical switching and plasmon-based information processing.

Multiple plasmon-induced transparency effects in a multimode-cavity-coupled metal–dielectric–metal waveguide

We numerically and theoretically investigate multiple plasmon-induced transparency (PIT) effects in a multimode-cavity-coupled metal–dielectric–metal (MDM) waveguide system. The introduced multimode coupled-radiating oscillator theory (MC-ROT) gives a clear understanding of multiple PIT effects in the proposed system. Two and three PIT peaks appear in the transmission spectra corresponding to the symmetrical and asymmetrical structures, respectively. Evolution of the PIT peaks can be effectively tuned by adjusting the geometric dimensions and asymmetry of the structure. The ultra-compact plasmonic waveguide structure may have important applications for multichannel filters, optical switches, and other devices in integrated optical circuits.

Tunable and Selective Transmission Based on Multiple Resonance Modes in Side-Coupled Sectorial-Ring Cavity Waveguide

We report plasmonic waveguide side-coupled with sectorial-ring cavity resonator which is called as side-coupled sectorial-ring cavity waveguide, and study the transmission performance of the novel system with oversize central angle, alterable symmetry plane angle, and fixed radius and gap. It is found from the two-dimensional simulation that the novel system excites the extra noninteger resonance modes, in contrast to the circular-ring cavity resonator system which can support only the classical integer resonance modes. The results show that the multiple resonance modes of the novel system can be highly tuned and modified by manipulating the size of central angle or the position of symmetry plane angle; the central angle has similar and different influences on resonance wavelengths and minimum transmittances, and the symmetry plane angle is almost unchanged on resonance wavelengths but has different changes on minimum transmittances. Interestingly, these resonance modes are extremely sensitive to the symmetry plane angle, the associated modes can be efficiently selected and improved by enhancing, weakening, exciting, or disappearing, and the maximum intensities occur at TM0.5(ϕu2009=u2009135o), TM1(ϕu2009=u20090o), TM1.5(ϕu2009=u200945o), TM2(ϕu2009=u20090o or 90o), and TM2.5(ϕu2009=u200945o), respectively. The proposed structure not only forms split-ring-like and realizes asymmetrical cavity, but also achieves tunable and selective transmission. Our results indicate that the plasmonic nanodevice is a promising candidate as a tunable and selective multichannel nanofilter or nanosensor in nanophotonics applications, and the optical technique provides a good flexibility to accurately design the transmission spectrum with prospective modes in integrated nano-optics devices.

Sensing analysis based on tunable Fano resonance in terahertz graphene-layered metamaterials

We theoretically investigate the sensing characteristics based on tunable Fano resonance in terahertz graphene-layered metamaterials. A Fano phenomenon comes from destructive interference in a narrow frequency range, and it can lead to a high figure of merit of ∼9786. A simple model for sensitivity is presented, and the sensitivity can reach up to 7885u2009nm/RIU. Besides, the Fano peak becomes more and more unobvious as symmetry breaking slowly recovers. We use an appropriate theoretical theory to explain the generation of Fano phenomena. Our proposed structure and investigation may pave the way for fundamental research of nanosensor applications and designs in highly integrated optical circuits.