Hai Ming

All-optical switching in subwavelength metallic grating structure containing nonlinear optical materials

All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmons enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.

Beam manipulating by metallic nano-optic lens containing nonlinear media.

Embedding nonlinear media in the slit region of metallic nano-optic lens is proposed as a new method of active modulating the output beam. Two important phenomena, beam deflection and focusing, have been studied in detail. A developed Finite Difference Time Domain (FDTD) method has been performed to account for the nonlinear response. The simulated results show that the deflection angle and focus length can be controlled easily by the intensity of incident light in the structures. The physical principle of the phenomena is explained by the Surface Plasmons (SPs) excitation and Fabry-Pérot (F-P) resonance in the nanoslit.

Optical bistability enhanced by highly localized bulk plasmon polariton modes in subwavelength metal-nonlinear dielectric multilayer structure

Optical bistability of subwavelength metal-nonlinear dielectric multilayer structure is numerically studied in this letter. It is found that very low intensity thresholds for optical bistability can be achieved due to the excitation of highly localized bulk plasmon polariton modes with TM polarized illumination. A bistability threshold of 6.9u2002MW/cm2 is obtained for BPP0 mode, which is much lower than the recently reported results based on the large local field enhancement at the band edge of metal-dielectric photonic band gap structure [A. Husakou and J. Herrmann, Phys. Rev. Lett. 99, 127402 (2007)].

Optical bistability in subwavelength metallic grating coated by nonlinear material

A developed two-dimensional Finite Difference Time Domain (FDTD) method has been performed to investigate the optical bistability in a subwavelength metallic grating coated by nonlinear material. Different bistability loops have been shown to depend on parameters of the structure. The influences of two key parameters, thickness of nonlinear material and slit width of metallic grating, have been studied in detail. The effect of optical bistability in the structure is explained by Surface Plasmons (SPs) mode and resonant waveguide theory.

Multimode interference splitter based on dielectric-loaded surface plasmon polariton waveguides.

We numerically demonstrated 1 x N multimode interference (MMI) splitters based on dielectric-loaded surface plasmon polariton waveguides (DLSPPW). The dependences of real part of effective index, propagation length and lateral mode profiles of the waveguides on the geometrical parameters are analyzed in detail. The transmission efficiency of the MMI splitter is as much as 60%, with their splitting length being in the range of several micrometers. The performance of the device is found in agreement with results predicted by theoretical MMI self-imaging theory. Such MMI splitter is important for implementation of high density photonic integration and lab-on-a-chip applications.

Plasmonic racetrack resonator with high extinction ratio under critical coupling condition

In this paper, an ultracompact plasmonic racetrack resonator based on single mode metal-insulator-metal plasmonic gap waveguide with high coupling efficiency is investigated both analytically and numerically. The coupling properties of a plasmonic waveguide to a racetrack resonator at 1.55u2002μm wavelength are studied with various coupling lengths. An extinction ratio of −34.5 dB and a free-spectral range of 303 nm at the critical coupling point can be achieved. Such a plasmonic resonator design provides a promising realization for highly effective modulators and wide band filters.

Numerical simulation of nanolithography with the subwavelength metallic grating waveguide structure

Metallic waveguide theory has been used to design subwavelength metallic grating waveguide structure which can excite the waveguide modes, especially the low frequency coupled surface plasmons mode, to achieve sub-50nm resolution lithography pattern by using the light with 436nm wavelength. The Finite Difference Time Domain method has been performed to analyze the performance of lithography pattern generated by two possible schemes. One named metal-layer scheme utilizes three different modes (two coupled surface plasmons and one non-coupled surface plasmons) on the metal layer to generate the lithography patterns with different resolution and visibility. The other named metal-cladding scheme excites the coupled mode in the metal-cladding region, which utilizes multi-layer coupled effect to generate the field with higher resolution (~ 34nm) and approximately same visibility compared with the metal-layer scheme. The effectively deviated range of grating period is also analyzed to keep the output pattern effective for the lithography.

Tunable plasmonic coupling between silver nano-cubes and silver nano-hole arrays

A quasi-three-dimensional (quasi-3D) system composed of Ag nano-cubes and Ag nano-hole arrays was fabricated through a low cost chemical process. The coupling of localized surface plasmons (LSPs) in the cube-hole array system has been investigated through surface-enhanced Raman scattering (SERS) from Rhodamine 6G (R6G) molecules. A SERS enhancement factor as large as 1.1 × 10(8) can be achieved due to this plasmonic coupling effect, and is highly sensitive to geometrical parameters, such as cube-hole array distance, hole diameter, inter-hole spacing and Ag film thickness.

Investigation of enhanced and suppressed optical transmission through a cupped surface metallic grating structure

Two-dimensional finite-difference time-domain (FDTD) method has been performed to numerically investigate the transmission through a one-dimension cupped surface metallic grating structure. The concept of coupling of optical modes in the notches and main slits, introduced by Crouse and Keshavareddy [1], is examined further in our work. Unexpected phenomenon is shown that even horizontal surface plasmons (HSPs) are inhibited, the transmission still can be enhanced or suppressed. And the periodicity of transmission depending on the phase change of the light striking on the grating surface is discovered. A hybrid optical mode combined by cavity mode and diffracted evanescent wave mode [2] is introduced to analyze the phenomenon.

A Planar Metallic Collimator Based on Controlling Surface Plasmons's Phase

We present numerical study of the optical transmission of a metal film perforated by slits array with different spacing. A planar metallic collimator with phase retardation controlled by the slits space is designed. The analysis results show this structure with appropriate space between the slits can collimate or deflect the transmitted beam, which is attributed to phase retardation of surface plasmons propagating from one slit to the other. The numerical analysis results demonstrate a useful deflecting or collimating function of a planar metallic film in the applied fields of optical storage, optical coupler, nano-optics.