Planar Plasmonic Metamaterials Research Articles

Ultra-wideband chiroptical response by tri-layer anisotropic plasmonic metamaterial

The use of plasmonic chiral metamaterials for the control of circular polarization has the potential to replace conventional optical equipment for polarization-related applications. The ultra-broadband chiroptic response using plasmonic constituents is delivered by elaborate three-dimensional (3D) helical structures, nevertheless, their implementation is complicated, time-consuming, and poses a significant scaling difficulty at the nano level. Ultra-broadband response from planar constituents is particularly necessary as a means to circumvent the challenges of 3D metamaterials. Here we present a planar plasmonic structure composed of tri-layer anisotropic arrays constituting nanowires and cut-wires to generate dual overlapped chiral bands. Based on this tri-layer approach, we numerically realized ultra-broadband planar plasmonic metamaterials to function in the near- and mid-infrared regions with a bandwidth range of 1.38–3.07 µm and 4.00–8.10 µm, and maximum circular dichroism performance of 0.90 and 0.92 respectively. The structures are ultracompact, misalignments tolerant, and can be extended to additional spectral regions through structural engineering. The proposed metamaterial has the potential to be used in the creation of ultra-compact, high-performance devices for a wide variety of uses, such as those in the fields of optical communication, biological diagnosis, high-contrast polarization imaging, high-accuracy polarimetric measurements, and spectroscopy.

Localized surface magnetic modes transfer along bend and T-splitter chain arrays of subwavelength metamaterial resonators

We present a coupled resonator optical waveguide (CROW) based on planar plasmonic metamaterials, which consists of metallic spiral structures arrays. The waveguide can confine the energy in subwavelength scale and transport spoof magnetic LSPs modes. Attributing to these features, the bend waveguide and T-splitter are designed. To verify the functionality and performance of the proposed waveguides, we implemented microwave simulations and experiments. The tested waveguide performances have clearly validated the functionality of our designs. It is believed to be applicable for future plasmonic circuit in microwave and THz ranges.

Optical magnetism and optical activity in nonchiral planar plasmonic metamaterials.

We investigate optical magnetism and optical activity in a simple planar metamolecule composed of double U-shaped metal split ring resonators (SRRs) twisted by 90° with respect to one another. Compared to a single SRR, the resonant energy levels are split and strong magnetic response can be observed due to inductive and conductive coupling. More interestingly, the nonchiral structures exhibit strong optical gyrotropy (1100°/λ) under oblique incidence, benefiting from the strong electromagnetic coupling. A chiral molecule model is proposed to shed light on the physical origin of optical activity. These artificial chiral metamaterials could be utilized to control the polarization of light and promise applications in enantiomer sensing-based medicine, biology, and drug development.

K-dispersion engineering of spoof surface plasmon polaritons for beam steering.

In this paper, we propose to achieve beam steering by k-dispersion engineering of spoof surface plasmon polaritons (spoof SPP) at microwave frequencies. The planar plasmonic metamaterials (PPMs) are employed to couple and guide spoof SPP. High-efficiency transmission based on spoof SPP coupling is realized via matching the wave-vectors of the spoof SPP and the space wave. The transmission phase can be modulated by k-dispersion engineering of the spoof SPP with great freedom. Due to the independent phase shift produced by the spoof SPP on the PPMs, the phase gradient achieved by using the PPMs as the sub-unit cells can be altered by changing the repetition period of the sub-unit cells. Two phase gradient materials (PGMs) are achieved by using nine different PPMs as the sub-unit cells with the repetition period q = 4mm and 4.5mm. Both the simulated and measured results demonstrated the excellent performances of the PGMs on high efficiency, wideband, tunable beam steering.

Ultra-wideband surface plasmonic Y-splitter.

We present an ultra-wideband Y-splitter based on planar THz plasmonic metamaterials, which consists of a straight waveguide with composite H-shaped structure and two branch waveguides with H-shaped structure. The spoof surface plasmonic polaritons (SSPPs) supported by the straight waveguide occupy the similar dispersion relation and mode characteristic to the ones confined by the branch waveguides. Attributing to these features, the two branch waveguides can equally separate the SSPPs wave propagating along the straight plasmonic waveguide to form a 3dB power divider in an ultra-wideband frequency range. To verify the functionality and performance of the proposed Y-splitter, we scaled down the working frequency to microwave and implemented microwave experiments. The tested device performances have clearly validated the functionality of our designs. It is believed to be applicable for future plasmonic circuit in microwave and THz ranges.

Optical Tamm state and related lasing effect enhanced by planar plasmonic metamaterials

Optical Tamm state (OTS) refers to a kind of interface state between the metal layer and the photonic crystal (PC) reflectors. Given the matching conditions being satisfied, the electromagnetic waves tend to tunnel through the metal-PC hetero-structure efficiently. Quite different from the conventional surface plasmon polaritons (SPPs) on metal surface, OTSs can be excited directly by normally incident propagating waves for both TE and TM polarizations to occur. In the meantime, strong electromagnetic (EM) localization around the interface can be achieved, leading to potential applications such as polariton lasers, enhancement of Faraday rotation, various nonlinear effects, and so on.#br#To further enhance the EM localization around the interface, some well designed artificial structures are patterned on the thin metal layer. For instance, confined Tamm plasmon modes with the aid of metallic microdisks are proposed by Gazzano et al. to control the spontaneous optical emission. Moreover, in 2013 it was also demonstrated that planar plasmonic metamaterials (PPM) with electromagnetically-induced-reflection-like (EIR-like) dispersion can boost the Q-factor of OTS tunneling mode, as well as the EM localization around the interface between planar plasmonic metamaterials and PC. Both these methods can be understood in the same scheme:the structure-induced dispersion provides exotic power of modulating the propagation of OTS.#br#In this paper, the enhancement of optical Tamm state and related lasing effect is investigated by introducing planar plasmonic metamaterials with EIR-like dispersion. The planar plasmonic metamaterials are achieved by periodic patterning some plasmonic units on the planar metal layer. Through fine tuning each unit cell, EIR-like dispersion can be achieved, making the properties of hetero-structure more tunable. One-dimensional photonic crystals composed of TiO2/SiO2 are also designed properly to support the optical Tamm state in PPM-PC hetero-structure. First, to analyze the possibility of enhancing local electromagnetic field density of optical Tamm state, a transfer matrix method is performed when EIR-like dispersion of PPM structure is hired. Next, full wave simulations based on FDTD method are also carried out to verify a hetero-structure composed of PPM and one-dimensional photonic crystal embbed with gain media. By introducing gain medium into (or near) the PPM structure, where the maximum local electromagnetic field density exists, the lasing effect is found obviously enhanced. Better emitting efficiency and monochromic response can be observed compared to the common metal-PC hetero-structure. These features make our structure promising to reduce the lasing threshold, enhance the fluorescence, and so on.

Spoof surface plasmon polaritons supported by ultrathin corrugated metal strip and their applications

AbstractIn this review, we present a brief introduction on the spoof surface plasmons supported on corrugated metallic plates with nearly zero thickness. We mainly focus on the propagation characteristics of spoof surface plasmon polaritons (SPPs), excitation of planar SPPs, and several plasmonic devices including the bending waveguide, Y-shaped beam splitter, frequency splitter, and filter. These devices are designed and fabricated with either planar or conformal plasmonic metamaterials, which are validated by both full-wave simulations and experiments, showing high performance. We also demonstrate that an ultrathin textured metallic disk can support multipolar spoof localized surface plasmons, either with straight or curved grooves, from which the Fano resonances are also observed.

Monopole resonators in planar plasmonic metamaterials.

We first present a new phenomenon: the quarter-wavelength resonance of an electromagnetic field in planar plasmonic metamaterials consisting of asymmetrically coupled air-slot arrays, which is essential for a monopole resonator. The anti-nodal electric field intensity of the quarter-wavelength fundamental mode is formed by strong charge concentrations at the sharp metallic edges of the crossing position of the air-slots, and the nodal point of the electric field intensity naturally occurs at the other end of the air-slot. By tuning the structural asymmetry, the quarter-wavelength resonances were successfully split from the half-wavelength resonance, experimentally and numerically.

Planar plasmonic metamaterial on a thin film with nearly zero thickness

We propose a planar plasmonic metamaterial on thin corrugated metal films in microwave and terahertz frequencies. From theoretical simulation and experiment, we show that spoof surface plasmon polaritons (SPPs) can propagate along a thin metal film by corrugating its edge with periodic array of grooves. We demonstrate that such a planar plasmonic metamaterial can sustain highly localized SPPs along two orthogonal directions. We have designed and simulated a planar ring resonator in the terahertz frequency, and made experiment in the microwave frequency, both of which exhibit excellent performance. The proposed planar plasmonic metamaterials can play important roles in integrated plasmonic circuits and systems.

Ultrathin dual-band surface plasmonic polariton waveguide and frequency splitter in microwave frequencies

We present an ultrathin dual-band plasmonic waveguide and frequency splitter experimentally based on designer surface plasmon polaritons (DSPPs) of planar composite periodic gratings. In such planar plasmonic metamaterials, the electromagnetic wave can be tightly confined around an ultrathin metallic grating, and the propagation of DSPPs strongly depends on the dispersion relation determined by the depth of groove. Based on such features, we design and fabricate an ultrathin composite grating to support two DSPP modes, which exhibit low bending loss in the bending surface plasmon polariton (SPP) waveguide. We further propose an ultrathin SPP frequency splitter by adjusting the groove depths of two branches. The experimental results are in good agreement to the numerical simulations.

Optical Tamm states in hetero-structures with highly dispersive planar plasmonic metamaterials

Optical Tamm states (OTSs) in hetero-structures consisting of highly dispersive planar plasmonic metamaterials and truncated photonic crystal (PC) are investigated numerically. Compared to conventional OTSs in metal-PC structures, the reflectance of tunneling mode can be reduced from −10.2 dB to −32.0 dB, with an optimized Q-factor up to 17 times higher simultaneously. Further study on electromagnetic (EM) field distribution confirms that EM waves are highly localized at some special points. The confinement along the propagating direction provided by OTSs and the in-plane localization originated from the planar plasmonic metamaterials give rise to the three-dimensional enhancement of sub-wavelength EM localization corporately. As the advantages above are not at a cost of extra device volume, this structure is promising to be applied in highly sensitive dielectric sensing, nonlinear optical devices, and so on.

Q-factor enhancement in a one-dimensional photonic crystal cavity with embedded planar plasmonic metamaterials

We report Q-factor enhancement in a one-dimensional (1D) photonic crystal (PC) cavity by embedding electromagnetic-induced-transparency (EIT) planar plasmonic metamaterials in the cavity. Microwave experiments show tenfold Q-factor enhancements, confirming the numerical simulations. More importantly, the Q-factor enhancement is mainly due to both the longitudinal and lateral confinements contributed by the 1D PC cavity and the planar EIT metamaterials, respectively. The combined PC-EIT structure with a prominent cavity figure of merit may find new applications in nonlinear optics, cavity quantum electrodynamics, and low-threshold lasers.