Optical Transmission Through Multilayered Ultra-Thin Metal Gratings

Optical transmission properties of multilayered ultra-thin metal gratings are numerically studied. The transmission spectrum has a broad stop-band with extremely low transmittance compared to that of a single-layer one for TM polarization. The stop-band is shown to be formed by multiple-interference tunneling and various plasmon resonance processes in ultra-thin-metal and dielectric multilayers. That is on the transmission background of non-apertured metal/dielectric multilayer structures that have low transmission in the long-wavelength range due to destructive multiple-interference tunneling, the transmission is further suppressed in the stop-band by plasmon resonances in the top metal/dielectric layers, e.g., the anti-symmetric bound surface plasmon mode in the ultra-thin metal layer and the gap surface plasmon mode in the metal-sandwiched dielectric layer. High transmission beyond the stop-band is due to coupled gap surface plasmon mode in the entire multilayer structures. Applications of the optical properties of the multilayered ultra-thin metal gratings are suggested for optical filtering (wavelength or polarization selective).     

Surface Plasmon Polaritons Probed with Cold Atoms

Plasmonics - We report on an optical mirror for cold rubidium atoms based on a repulsive dipole potential created by means of a modified recordable digital versatile disc. Using the mirror, we have...     

Complicated Wavefront Shaping of Surface Plasmon Polaritons on Metal Surface by Holographic Groove Patterns

Surface plasmon polaritons (SPPs) manipulation on metal surfaces is important for constructing ultracompact integrated micro/nano-optical devices and systems. We employ the methodology of surface electromagnetic wave holography (SWH) to design holographic groove patterns for controlling SPPs with complicated wavefronts traveling on metal surface. SPPs are scattered by these deli groove patterns and interfere with each other to form desired SPP wavefronts. Several devices are demonstrated to control the intensities and phases of SPPs, such as focusing a plane SPP or diverging SPPs to two points with different phases, and focusing SPPs with complicated beam profile to a point. The finite-difference time-domain simulations show that in all cases, the predesignated functionalities are fully achieved by the designed plasmonic holographic structures. The results strongly support the power of SWH for shaping the complicated wavefront of in-plane transporting SPPs.     

Graphene Hybrid Surface Plasmon Waveguide with Low Loss Transmission

In this paper, a novel graphene hybrid surface plasmon waveguide structure is designed. Based on the finite element method, the mode characteristics, the quality factor, and the gain threshold of the waveguide structure are analyzed. The results show that the optical field constraint of the designed waveguide can reach a better level of deep sub-wavelength under the optimal parameters of 1550-nm working wavelength. The structure is applied to a laser, and the high quality factor, the low energy loss, the low threshold limit, and the ultra-small effective mode field area are obtained by adjusting waveguide design parameters. Compared with the common waveguide structure, this structure has stronger optical field limiting ability and microcavity binding ability. It provides theoretical and technical support for the development of new high-efficiency nano-laser devices and is expected to be applied to fields such as on-chip interconnects, photonic integrated circuits, optical storage, and optical signal processing.

     

Spectral Shifting in Extraordinary Optical Transmission by Polarization-Dependent Surface Plasmon Coupling

Plasmonics - Nanoapertures in a metallic film exhibit extraordinary optical transmission (EOT) owing to the surface plasmon resonance. Their transmission properties are known to be dependent on the...     

An Efficient Large-Area Grating Coupler for Surface Plasmon Polaritons

We report the design, fabrication, and characterization of a periodic grating of shallow rectangular grooves in a metallic film with the goal of maximizing the coupling efficiency of an extended plane wave (PW) of visible or near-infrared light into a single surface plasmon polariton (SPP) mode on a flat metal surface. A PW-to-SPP power conversion factor >45% is demonstrated at a wavelength of 780?nm, which exceeds by an order of magnitude the experimental performance of SPP grating couplers reported to date at any wavelength. Conversion efficiency is maximized by matching the dissipative SPP losses along the grating surface to the local coupling strength. This critical coupling condition is experimentally achieved by tailoring the groove depth and width using a focused ion beam.     

Low-Frequency Surface Plasmon Polaritons Guided on a Corrugated Metal Striplines with Subwavelength Periodical Inward Slits

A new type of stripline-based microwave transmission, which has relatively lower crosstalk compared with the conventional striplines, is proposed. The structure is formed by corrugated inward slit that is subwavelength scale on the edge of the stripline via the photolithography techniques. Numerical simulation is used to analyze the transmission and dispersion properties of this new stripline structure, and the results are experimentally verified in the frequency range from 200 MHz to 8 GHz. We found that spoof surface plasmon polaritons are supported on the new stripline structure whose electromagnetic fields are highly localized near the stripline, and hence the coupling is suppressed between the present type of stripline and the conventional stripline. For a structured stripline and a conventional stripline which are parallelly placed and separated by a distance of the stripline width, the crosstalk between them ranges from −17.13 to −64.89 dB, which is much lower than the crosstalk between two coupled conventional striplines. As this new type of stripline has such an important advantage, it would be applicable to high-density microwave circuits or high-speed circuits.     

Deep-subwavelength Guiding and Superfocusing of Spoof Surface Plasmon Polaritons on Helically Grooved Metal Wire

Deep-subwavelength guiding and superfocusing of spoof surface plasmon polaritons (SSPPs) realized on a helically grooved metal wire at microwave frequencies are presented in this paper. Two smooth bridges with gradient helical grooves decorated on the cylindrical and conical metal wire are proposed and designed, respectively. High-efficiency and broadband mode conversion from the traditional guided waves to the SSPPs and superfocusing of SSPPs are reported. Numerical simulations quantitatively show that the amplitudes of electric field at the tip of the conical wire with gradient helical grooves can be magnified 50 times more than that of the input signal in broadband. Moreover, the second transition structure ensures that the depth of helical groove can be tuned flexibly and arbitrarily, making it compatible with all kinds of N-type coaxial connectors. Strong field concentration and superfocusing of these two structures can be easily extended to terahertz (THz) frequencies by tuning the geometrical parameters and can find important applications in sensing, spectroscopy and near-field imaging in the microwave and THz frequencies.     

Metasurface Lens for both Surface Plasmon Polaritons and Transmitted Wave

Metasurface lenses which could simultaneously focus both surface plasmon polaritons (SPPs) and transmitted wave are designed. This kind of device is composed of slit antennas and is optimized with the simulated annealing algorithm to realize a single-focus or double-focus lens. Interestingly, the focusing of SPPs is polarization dependent while the focusing of the transmitted wave is immune from the polarization of incident light. The proposed methodology may inspire more designs of device steering both surface wave and transmitted wave.     

Conditions for Loss Compensation of Surface Plasmon Polaritons Propagation on a Metal/Gain Medium Boundary

One way to compensate for the surface plasmon polariton (SPP) propagation losses is to use a gain medium. However, simply ensuring high enough gain is not sufficient because it may violate the bounded character of the wave. Therefore, a detailed theoretical analysis is needed for the determination of the conditions for lossless or amplified SPP propagation. Here presented is an exact theoretical analysis of the SPP propagation in the case of an infinite metal/gain medium boundary. It is shown that the conditions for lossless/amplified SPP propagation can be conveniently examined and presented as a simply connected region in the complex plane of the gain medium dielectric function. Effective and minimum gain parameters are introduced, which facilitates the simultaneous analyses of different gain media/metals combinations. The practical application of these results is illustrated for several gain media/metal (silver, gold and aluminium) systems.     

Metal-Dielectric Composite Holography for Controlling the Propagations of Surface Plasmon Polaritons

Plasmonics - Controlling the propagations of surface plasmon polaritons (SPPs) is important for many applications. Now, mainly structures for controlling SPPs are etched directly in the metal...     

Design of a Slit-Groove Coupler for Unidirectional Excitation of the Guided Surface Plasmon Polaritons Through a Plasmonic Slot Waveguide

In this paper, a plasmonic-photonic nanostructure has been introduced for efficient unidirectional coupling of free-space radiation to surface plasmon polariton (SPP) waves under normal illumination on a subwavelength slit. The structure consists of a conventional metallic slit-groove nanostructure integrated with a plasmonic waveguide to support SPP waves along the desired direction with a remarkable lateral confinement. The unidirectional coupling is achieved by using an integrated plasmonic distributed reflector designed under Bragg condition. This reflector basically distributes part of the light coupled through the slit into the SPP modes of the waveguide. Numerical simulations show that up to 26 % of the normally incident light couples to the transversely localized field of the surface plasmon. In addition, the ratio of mode current density of the surface plasmon, launched in the desired direction, to that in the opposite direction can reach about 23 times. This structure shows a 2.5-fold improvement in coupling efficiency relative to a standard slit-groove structure. Also, the transmission distance for the new nanostructure is shown to be more than 8 times greater than that of the standard nanostructure.     

Combination of Surface Plasmon Polaritons and Subwavelength Grating for Polarization Beam Splitting

Plasmonics - A polarization beam splitter (PBS) based on the plasmonic subwavelength grating (PSWG) is proposed and investigated. The PBS is composed by a directional coupler with a PSWG as the...     

Enhanced Directed Radiative Surface Plasmon Emission from Periodically Corrugated Noble Metal Films

Plasmonics - Massively enhanced directed radiation emission from periodically corrugated thin gold and silver films at the surface plasmon resonance is reported. The optical setup comprises...     

3D-FDTD Modeling of Angular Spread for the Extraordinary Transmission Spectra of Metal Films with Arrays of Subwavelength Holes

Extraordinary transmission through a metal film with an array of subwavelength holes (mesh) can be modeled effectively using three-dimensional finite difference time domain (3D-FDTD) calculations. A simple 3D-FDTD model, where a plane wave of light at perpendicular incidence with no angular spread interacts with a periodic repeating mesh, models the shape and location of the transmission resonance peaks qualitatively but not quantitatively. The simple 3D-FDTD model gives peaks that are tall, sharp, and red-shifted compared to experimental measurements using a benchtop Fourier transform infrared (FTIR) spectrometer. It was discovered that the simple model does not account accurately for diffraction order scattering by the mesh or the angular spread of the actual FTIR beam. This work describes a more sophisticated model that accounts for these factors and agrees quantitatively with experimental FTIR results.     

Coated Drop-Shaped Nanowires for Guiding THz Surface Plasmon Polaritons with Nanoscale Confinement and Ultra-Long Propagation Distances

Focusing far beyond the diffraction limit is very important for terahertz (THz) wave applications due to its much longer wavelength compared with optical wave. Surface plasmon polaritons (SPPs) on metal wires are frequently used to attain this focusing. However, when the mode width is reduced down to the nanometer scale, the mode loss is very high. Here, a coated drop-shaped nanowire (CDSN) is proposed for guiding THz SPPs with both ultra-strong mode confinement (10 nm) and extreme-long propagation length (1~15 mm), which result from the distinctive mode fields around the top and bottom arcs, respectively, of the metal wire. The fantastic mode properties make the waveguide very useful in nanophotonics, bio-photonics, and highly integrated photonic circuits.     

Centrally Symmetric Focusing of Surface Plasmon Polaritons with a Rectangular Holes Arrayed Plasmonic Lens

Plasmonics - Nano rectangular holes etched in a gold thin film are optimized and arrayed to form a plasmonic lens. We demonstrate both theoretically and numerically that the proposed plasmonic lens...