Yueke Wang

Plasmonic-Induced Transparency in Metal–Dielectric–Metal Waveguide Bends

We have numerically investigated an analog of electromagnetically induced transparency (EIT) in a metal–dielectric–metal (MDM) waveguide bend. The geometry consists of two asymmetrical stubs extending parallel to each arm of a 90° MDM waveguide bend. Finite-difference time-domain (FDTD) simulations show that a transparent window is located at 1550 nm, which is the phenomenon of plasmonic-induced transparency (PIT). The large group index up to 63 can be obtained at the PIT window. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. Our proposed configuration may thus be applied to storing and stopping light in plasmonic waveguide bends.

Transmittance characteristics and tunable sensor performances of plasmonic graphene ribbons

We investigate the transmittance characteristics of graphene ribbons numerically. It is found that the transmission dips originate from the transverse and longitudinal resonances of edge graphene plasmon modes, supported by the graphene ribbon resonator. The environmental refractive index changes are detected by measuring the resulting spectral shifts of the resonant transmission dip, so the graphene ribbons can be applied to plasmonic sensor in infrared. Simulation results show that sensing performances for each resonant mode are similar, and figure of merit can be up to 6. Beside, thanks to the tunable permittivity of graphene by bias voltages, the transmittance spectra and sensor performances can be easily tuned.

Detuned square ring resonators for multiple plasmon-induced transparencies in metal–insulator–metal waveguide

We propose a metal–insulator–metal (MIM) waveguide with two detuned square ring resonators to achieve on-chip multiple plasmon-induced transparencies (PITs). PITs can be explained by a well-defined phase coupling that can be established between detuned resonances. For third-order detuned resonances, there is one PIT window. For second-order detuned resonances, there are one, two, or three PIT windows, depending on the detuning degree between the two square ring resonators. Electromagnetic simulation based on the finite element method is carried out to calculate the PIT transmission spectrum and electromagnetic field distribution.

A dual-way directional surface-plasmon-polaritons launcher based on asymmetric slanted nanoslits

We theoretically design a device composed of two asymmetric slanted nanoslits to achieve the directionality of surface plasmon polaritons (SPPs). With proper inclination of the two slits, the desirable relative phase delay can be obtained. When the structure is illuminated by normal incident light, the SPPs can be controlled to deflect the specific direction due to light interference. The SPPs can be altered to the opposite direction when the illuminating light is changed inversely. We develop another way to tailor the relative phase delay by choosing the specific effective index for each slanted slit. In order to acquire higher directional excitation efficiency, our designs have been extended to periodic structures with the pairs of slanting slits. The finite element method is carried on to verify our designs. The simulations show that the best proportion of the SPP field intensity along two opposite directions reaches to around 30.

Actively controlled plasmonic Bragg reflector based on a graphene parallel-plate waveguide

We investigate theoretically and numerically a graphene parallel-plate waveguide structure with two alternate chemical potentials (which can be realized by alternately applying two biased voltages to graphene). A plasmonic Bragg reflector can be formed in infrared range because of the alternate effective refractive indexes of SPPs propagating along graphene sheets. By introducing a defect into the Bragg reflector, and then the defect resonance mode can be formed. Thanks to the tunable permittivity of graphene by bias voltages, the central wavelength and bandwidth of SPPs stop band, and the wavelength of the defect mode can be tuned.

Two-Way Directional Plasmonic Excitation with Two Unsymmetrical Metallic Slits

The model of two-way directional plasmonic excitation is firstly proposed in theory. The structure is composed of a silver film, perforated with two unsymmetrical nanoslits. Under the designed parameters based on surface plasmon polaritons (SPPs) interference, the SPPs are excited unidirectionally under the backside illumination. The unidirectional propagation direction of the SPPs can be tuned to the opposite when the excited light is changed from one surface of the silver layer to another. The field distribution of the structure is investigated by using the finite-difference time-domain (FDTD) method to verify our design.

Transmission characteristics and transmission line model of a metal-insulator-metal waveguide with a stub modified by cuts.

We propose a structure of a metal-insulator-metal (MIM) waveguide with a stub modified by cuts. Our simulation results, conducted by the finite element method, show that the wavelengths of transmission dip vary with the position of the cuts and form the zigzag lines. A transmission line model is also presented, and it agrees with simulation results well. It is believed that our findings provide a smart way to design a plasmonic waveguide filter at the communication region based on MIM structures.

Tunable plasmon-induced transparency with graphene-sheet structure

We investigate theoretically and numerically the tunable plasmon-induced transparency (PIT) phenomenon in graphene-sheet system in infrared range. We show that when surface plasmon polaritons (SPPs) propagate along a monolayer graphene sheet with two detuned side-coupled resonators, the PIT-like transmission spectra of SPPs appear. Thanks to the tunable permittivity of graphene by bias voltages, the resonant wavelength of side-coupled resonators can be changed. So the transmission spectra can be tuned dynamically and the tunable PIT phenomenon is achieved. Numerical simulation by finite element method is conducted to verify our design.

Accurate focal spot diagnostics based on a single shot coherent modulation imaging

A single-shot method based on coherent modulation imaging is presented for the diagnostics of the focal spot of laser facilities. The laser beam to be measured first illuminates a highly random phase plate with a known structure and subsequently the intensity of the resulting diffraction pattern is recorded by a charge-coupled device positioned behind the phase plate. Intensity distribution at the focus of the laser beam is accurately reconstructed with the coherent modulation imaging method. The feasibility of this method is demonstrated with an experiment involving a He–Ne laser.

Scattering-Suppressed Plasmonic Bends and Adapters with Gradient Refractive Index Medium

We propose the designs of plasmonic bends and adapters with low scattering loss in visible region theoretically. Tens of nanometers thick gradient refractive index medium is deposited on the metallic surface, which can confine and release the surface plasmon polaritons (SPPs). When SPPs can be strongly confined the metallic surface and propagate along the corners of the plasmonics devices, the scattering loss can be dramatically suppressed. Full wave simulations based on a finite element method have been performed to validate our proposal. Compared with the same class of design, our method can be achieved only with isotropic materials.