By exciting a plasmonic lens with femtosecond laser and utilizing the optical nonlinearity of the gold, an ultrasmall and ultrafast all-optical modulation spot was achieved inside a thin gold film. Near-field pump-probe measurements indicated a modulation spot size of about 600 nm, and a response time of about 1.5 ps. Even smaller spot size of about 300 nm was inferred from numerical simulations, beyond the diffraction limit given an incident wavelength of 1000 nm. Moreover, the optical nonlinearity and the modulation depth were increased by one order of magnitude at the focus compared to that at positions without structures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581895]
By coating a metal with a finite-thickness dielectric film, evident differences in the wave-vector magnitude between surface plasmon polaritons (SPPs) and quasicylindrical waves (quasi-CWs) emerge. This brings modulation patterns to the total field on the metal surface near the electromagnetic source. Based on such an effect, an ultracompact SPP splitter with a lateral dimension of only 800 nm is experimentally demonstrated at wavelengths of 740 nm and 832 nm in a dielectric-film-coated asymmetric single nanoslit. These results imply that the additional modulation of quasi-CWs to the total field provide new possibilities for the design of ultracompact plasmonic devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3564935]
Ultrahigh spatiotemporal resolved pump-probe signal near a gold nano-slit is detected by femtosecond-SNOM. By employing two-color pump-probe configuration and probing at the interband transition wavelength of the gold, signal contributed by surface plasmon polariton is avoided and spatiotemporal evolvement of excited electrons is successfully observed. From the contrast decaying of the periodical distribution of the pump-probe signal, ultrafast diffusion of excited electrons with a time scale of a few hundred femtoseconds is clearly identified. For comparison, such phenomenon cannot be observed by the one-color pump-probe configuration. (C) 2010 Optical Society of America
An asymmetric single-nanoslit composed of a conventional nanoslit with a nanogroove next to it in a metallic film is proposed to generate unidirectional surface plasmon polaritons (SPPs) efficiently with back-side illumination. Numerical simulations show that due to the different interference processes of SPPs to opposite directions, efficient unidirectional SPP generation can be achieved. Experimentally, an extinction ratio of about 30:1 for SPPs to opposite directions and a generation efficiency of about 1.8 times that of the symmetrical case are demonstrated at wavelength of 830 nm with the lateral dimension of the asymmetric single-nanoslit of only 370 nm. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3472251]
Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide (DLSPPW) based 1/4 circle is calculated for a 90 degrees bend model and a 270 degrees bend model, respectively. It is found that the 270 degrees bend model gives almost pure bending loss while the 90 degrees bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators (WRRs) and the results of the 270 degrees bend model agree well with direct simulating results of the WRRs. Thus the 270 degrees bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.
Ultrahigh spatiotemporal resolved pump-probe signal on a metal nanostructure is detected by femtosecond-SNOM. By using two-color pump-probe configuration, ultrafast hot electron transportation is clearly observed on a time scale of a few hundred femtoseconds. (C) 2010 Optical Society of America
We propose a refractive index sensor based on the interference of two surface-plasmon waves on both surfaces of a gold film with a two-slit structure. The phase of the interference was solved, and the dispersion relation of the real part of Au dielectric function was considered. The sensor was performed with NaCl-H(2)O solutions of different concentrations and exhibited a linear response and a high sensitivity of 4547 nm/RIU (refractive index unit) to the refractive index change. (c) 2009 Optical Society of America
A finite width dielectric-metal-dielectric (DMD) waveguide placed on a substrate is numerically investigated near the telecom wavelength lambda = 1550 nm by the finite element method. With proper waveguide sizes, the asymmetrical DMD waveguide can support hybrid long-range surface plasmon-polariton modes which have tight field confinement (similar to 700 nm) and long propagation lengths (L> 300 mu m) simultaneously. Compact plasmonic waveguide-ring resonators (WRRs) based on such asymmetrical DMD waveguide show high quality factors compared with dielectric-loaded surface plasmon-polariton, channel plasmon polariton, plasmonic whispering-gallery microcavity, and pure dielectric waveguide cases. (C) 2009 Optical Society of America
Long-range surface plasmon polariton (LRSPP) modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoretically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thicknesses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.
A simple, high efficiency and mini-sized surface plasmon polariton (SPP) modulator based on electro-optic polymer is proposed. The modulator is constructed by metallic stripes of Mach-Zender (M-Z) interferometric structure and with electro-optic polymer surrounding the stripes. The reflectivity index of the eleetro-optic polymer is modulated when the modulating voltage is applied to the two arms of the M-Z interferometer. Through the M-Z interferometer, the modulation of the reflectivity index can be transferred into the modulation of the SPP intensity. By calculating the electric field near the metallic stripes and taking the distribution of SPP field into account, the working principle of the SPP modulator is demonstrated in detail and the half-wave modulating voltage is evaluated as 2.8 V.