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The emerging field of plasmonics is based on exploiting the coupling between light and collective electronic excitations within conducting materials known as surface plasmons. Because the so-called surface plasmon polariton (SPP) modes that arise from this coupling are not constrained by the optical diffraction limit, it is hoped that they could enable the construction of ultracompact optical components 1,2 . But in order that such potential can be realized, it is vital that the relatively poor light-SPP coupling be improved. This is made worse by the fact that the incident light that is conventionally used to launch SPPs in a metal film 3-6 is a significant source of noise, unless directed away from a region of interest, which then decreases the signal and increases the system's size. Back-side illumination of subwavelength apertures in optically thick metal films 7-13 eliminates this problem but does not ensure a unique propagation direction for the SPP. We propose a novel back-side slit-illumination method that incorporates a periodic array of grooves carved into the front side of a thick metal film. Bragg reflection enhances the propagation of SPPs away from the array, enabling them to be unidirectionally launched from, and focused to, a localized point.A picture of the proposed surface plasmon polariton (SPP) launcher is shown in Fig. 1. A periodic array of one-dimensional indentations is fabricated at the (output) metal surface close and parallel to the illuminated slit. The design of this device is based on two facts. The first one is that the reflection of SPPs by a periodic array of indentations presents maxima at the low-l edges of the plasmonic bandgaps [14][15][16] . For subwavelength indentations, the spectral locations of these edges can be obtained by folding the dispersion relation of SPPs for a flat metal surface into the first Brillouin zone, satisfying the following expression:where P is the period of the array, k p holds for the in-plane plasmon wavevector and m is the band index. Remarkably, although the reflectance maxima depend on the groove geometry (width and depth) and the number of grooves, their spectral locations do not. The second fact is that the phase picked up by the SPP on reflection is just mπ, precisely at the condition given by

Addressing the fundamental question of miniaturization of light guiding and routing towards nanoscale optics, we study experimentally surface plasmon propagation in silver and gold thin films of finite widths in the micrometer range. Spatially confined excitation of surface plasmons is realized by a prism coupling arrangement involving an opaque aluminum screen for a distinct separation of excitation and propagation (measurement) region. The surface plasmon propagation length as a function of film widths is measured by detecting stray light due to surface plasmon scattering with a conventional optical microscope.

We analytically and numerically analyze the fluorescence decay rate of a quantum emitter placed in the vicinity of a spherical metallic particle of mesoscopic size (i.e with dimensions comparable to the emission wavelength). We discuss the efficiency of the radiative decay rate and non-radiative coupling to the particle as well as their distance dependence. The electromagnetic coupling mechanisms between the emitter and the particle are investigated by analyzing the role of the plasmon modes and their nature (dipole, multipole or interface mode). We demonstrate that near-field coupling can be expressed in a simple form verifying the optical theorem for each particle modes.

We show that interfering surface plasmon polaritons can be excited with a focused laser beam at normal incidence to a plane metal film. No protrusions or holes are needed in this excitation scheme. Depending on the axial position of the focus, the intensity distribution on the metal surface is either dominated by interferences between counterpropagating plasmons or by a two-lobe pattern characteristic of localized surface plasmon excitation. Our experiments can be accurately explained by use of the angular spectrum representation and provide a simple means for locally exciting standing surface plasmon polaritons.

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The launching of surface plasmons by micro-gratings of subwavelength apertures milled in a thick metal film is important for the development of surface plasmon based circuits. By comparing the near-field optical images of such surface plasmon sources with the results of a Huygens-Fresnel principle based scattering model, we show that the properties of the locally launched SP beams such as divergence or uniformity can be tuned by adjusting the shape of the micro-gratings. This allows us to propose an optimized source array well adapted for providing a narrow, collimated and uniform beam.

We demonstrate an efficient thermo-optic dielectric loaded surface plasmon polariton waveguide (DLSPPW) 2 × 2 switch using a high thermo-optic coefficient polymer and a dual mode interference configuration. Unlike previous configurations relying on single-mode waveguide circuitry, the switch we consider is based on the interference between a plasmonic and a low-damping photonic mode of the DLSPPW, thus leading to the minimization of insertion losses of the device. Switching extinction ratios of 7 dB are measured for a compact 119 μm-long device. The overall device performances are in good agreement with numerical simulations performed using the beam propagation method.