evaluating-plasmonic-transport-in-current-carrying-silver-nanowires

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information ...

University of Science and Technology of China

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.

Numerical simulation of nanolithography with the subwavelength metallic grating waveguide structure.

Phase modulation of surface plasmon polaritons (SPPs) is studied as a function of geometric length and thickness of surface relief dielectric structures on a metal film. The results indicate that the SPPs are analogous to conventional free-space light waves in terms of phase modulation by geometric sizes and refractive indices. An SPP Fresnel zoneplate is considered as an example to employ the phase modulation method for focusing enhancement at the focal point. It is found that the phase modulation optimized zoneplate has obtained 130% higher electric field intensity at the focal point than that of an amplitude-modulated zoneplate.

Phase modulation of surface plasmon polaritons by surface relief dielectric structures.

Leakage radiation microscopy (LRM) is used to directly image surface-plasmon-coupled emission (SPCE). When compared with the prism-based setup commonly used in SPCE research, LRM has the advantages of directly giving out the emitting direction without angle scanning, and the image generated of surface plasmon polariton (SPPs) propagation, which helps to understand the optical process of SPCE. LRM also can give a clearer SPCE image than that obtained by a prism-based setup. Based on the LRM, we find that the SPCE pattern and propagation of SPPs can be modified by the shape of PMMA films containing fluorescence molecules.

Direct image of surface-plasmon-coupled emission by leakage radiation microscopy.

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.

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

Using dual-plane leakage radiation microscopy, we investigate plasmon propagation in individual penta-twinned crystalline silver nanowires. By measuring the wavevector content of the light emitted in the substrate, we unambiguously determine the effective index and the losses of the mode propagating in these structures. The experimental results, in particular, the unexpectedly low effective index, reveal the direct influence of the nanowire crystallinity and pentagonal structure on the observed plasmon modes. By analogy with molecular orbitals of similar symmetry, the plasmon modes are also determined numerically in good agreement with the observed values. We further investigate the effect of wire geometry (length, diameter) on the effective index and propagation loss. Our results show that, beyond dissipation concerns, the morphological and structural control obtained in crystalline colloidal plasmonic nanostructures can be exploited to finely tune their optical properties.

Imaging symmetry-selected corner plasmon modes in penta-twinned crystalline Ag nanowires.

We demonstrate the realization of a coherent random fiber laser (RFL) in the extremely weakly scattering regime, which contains a dispersive solution of polyhedral oligomeric silsesquioxanes nanoparticles (NPs) and laser dye pyrromethene 597 in carbon disulfide that was injected into a hollow optical fiber. Multiple scattering of polyhedral oligomeric silsesquioxanes NPs greatly enhanced by the waveguide confinement effect was experimentally verified to account for coherent lasing observed in our RFL system. This Letter extends the NPs-based RFLs from the incoherent regime to the coherent regime.

Coherent random fiber laser based on nanoparticles scattering in the extremely weakly scattering regime.

Although surface-plasmon-coupled emission-based fluorescence microscopy proves high sensitivity for surface imaging, its donut shape point spread function (PSF) leads to low optical resolution and inefficient signal collection. In this Letter, we experimentally demonstrate the feasibility of solving this problem by the use of a liquid-crystal plate, which could convert the polarization state of surface-plasmon-coupled fluorescence from radial to linear. After being focused by the collection lens, an Airy disk-like PSF of small size can be realized. Experimental results reveal that both the lateral resolution and the signal-to-noise ratio can be enhanced simultaneously.

Surface-plasmon-coupled emission microscopy with a polarization converter.

In this paper, a high-Q/Veff gap-mode plasmonic Fabry-Perot nanocavity, which is composed of a silver nanowire on a flat silver substrate spaced by patterned dielectric distributed Bragg gratings, is investigated both analytically and numerically. The design parameters and properties of the nanocavity are exploited with the use of generalized Fabry-Perot model. The Veff ~0.0026 (λ/n)³ and Q/Veff ~1.4 × 10⁵/μm³ of the nanocavity can be achieved. Such a gap-mode plasmonic Fabry-Perot nanocavity design provides a promising realization for wide novel band filters and spaser.

High-Q/Veff gap-mode plasmonic FP nanocavity.

We have demonstrated the realization of a random polymer fiber laser (RPFL) based on laser dye Pyrromethene 597-doped one-dimensional disordered polymer optical fiber (POF). The stabilized coherent laser action for the disordered POF has been obtained by the weak optical multiple scattering of the polyhedral oligomeric silsesquioxanes nanoparticles in the core of the POF in situ formed during polymerization, which was enhanced by the waveguide confinement effect. Meanwhile, the threshold of our RPFL system is almost one order of magnitude lower than that of the liquid core random fiber laser reported previously, which promotes the development of random lasers.

Douguo Zhang

Department of Optics and Optical Engineering

University of Science and Technology of China

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires