There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space. Now plasmonics researchers are turning their attention to photovoltaics, where design approaches based on plasmonics can be used to improve absorption in photovoltaic devices, permitting a considerable reduction in the physical thickness of solar photovoltaic absorber layers, and yielding new options for solar-cell design. In this review, we survey recent advances at the intersection of plasmonics and photovoltaics and offer an outlook on the future of solar cells based on these principles.

Plasmonics for improved photovoltaic devices

Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

/pdf/plasmonics-fundamentals-and-applications-4syb9877sr.pdf

Plasmonics: Fundamentals and Applications

Electronic circuits provide us with the ability to control the transport and storage of electrons. However, the performance of electronic circuits is now becoming rather limited when digital information needs to be sent from one point to another. Photonics offers an effective solution to this problem by implementing optical communication systems based on optical fibers and photonic circuits. Unfortunately, the micrometer-scale bulky components of photonics have limited the integration of these components into electronic chips, which are now measured in nanometers. Surface plasmon-based circuits, which merge electronics and photonics at the nanoscale, may offer a solution to this size-compatibility problem. Here we review the current status and future prospects of plasmonics in various applications including plasmonic chips, light generation, and nanolithography.

/pdf/plasmonics-merging-photonics-and-electronics-at-nanoscale-3vxc7s7v4s.pdf

Plasmonics: merging photonics and electronics at nanoscale dimensions.

Recent years have seen a rapid expansion of research into nanophotonics based on surface plasmon–polaritons. These electromagnetic waves propagate along metal–dielectric interfaces and can be guided by metallic nanostructures beyond the diffraction limit. This remarkable capability has unique prospects for the design of highly integrated photonic signal-processing systems, nanoresolution optical imaging techniques and sensors. This Review summarizes the basic principles and major achievements of plasmon guiding, and details the current state-of-the-art in subwavelength plasmonic waveguides, passive and active nanoplasmonic components for the generation, manipulation and detection of radiation, and configurations for the nanofocusing of light. Potential future developments and applications of nanophotonic devices and circuits are also discussed, such as in optical signals processing, nanoscale optical devices and near-field microscopy with nanoscale resolution.

Plasmonics beyond the diffraction limit

Long-range surface plasmon polaritons (LRSPPs) are optical surface waves that
 propagate along a thin symmetric metal slab or stripe over an appreciable length
 (centimeters). Vigorous interest in LRSPPs has stimulated a large number of studies
 over three decades spanning a broad topical landscape. Naturally, a good segment of
 the literature covers fundamentals such as modal characteristics, excitation, and
 field enhancement. But a large portion also involves the LRSPP in diverse phenomena,
 including nonlinear interactions, molecular scattering, fluorescence,
 surface-enhanced Raman spectroscopy, transmission through opaque metal films and
 emission extraction, amplification and lasing, surface characterization, metal
 roughness and islandization, optical interconnects and integrated structures,
 gratings, thermo-, electro- and magneto-optics, and (bio)chemical sensing. Despite
 the breadth and depth of the research conducted to date, much remains to be
 uncovered, and the scope for future investigations is broad. We review the properties
 of the LRSPP, survey the literature involving this wave, and discuss the prospects
 for applications. Avenues for further work are suggested.

Long-range surface plasmon polaritons

The purely bound electromagnetic modes of propagation supported by asymmetric waveguide structures, comprised of a thin lossy metal film of finite width on a dielectric substrate and covered by a different dielectric superstrate, have been characterized at optical wavelengths. The dispersion of the modes with film thickness and width has been assessed and the effects caused by varying the difference between the superstrate and substrate dielectric constants on the characteristics of the modes have been determined. The modes are quite different from those supported by corresponding slab structures or similar finite-width symmetric waveguides. Unlike these limiting cases, the dispersion with film thickness can exhibit an unusual oscillatory character which is explained by a switching or swapping of the constituent interface modes. In addition, the four fundamental modes supported can evolve such that none has a diminishing attenuation with diminishing film thickness. This rather complex evolution of modes is unique to asymmetric finite-width structures. Under certain conditions, a long-ranging mode having a field distribution that is suitable to excitation using an end-fire technique can be supported. The long-ranging mode has a cutoff thickness below which it is no longer propagated, and its attenuation near cutoff decreases very rapidly, much more so than the attenuation related to the long-ranging mode in a comparable symmetric waveguide. Furthermore, its cutoff thickness is larger than that of the ${s}_{b}$ mode in the corresponding asymmetric slab waveguide, which implies that decreasing the film width increases the sensitivity of the mode to the asymmetry in the structure. This result is interesting and potentially useful in that the propagation characteristics of the mode can be affected by a smaller change in the dielectric constant of the substrate or superstrate compared with the ${s}_{b}$ mode guided by the corresponding slab structure.

Plasmon-polariton waves guided by thin lossy metal films of finite width: Bound modes of asymmetric structures

This Review provides an introduction to the compensation of loss and amplification of surface plasmons in waveguides and resonators. Future challenges, including how to overcome the large losses present in plasmonic systems that offer strong electromagnetic confinement, are also discussed.

Surface plasmon–polariton amplifiers and lasers

Surface plasmon–polaritions, collective electron oscillations coupled to light waves at the surface of a metal, show unique properties that are valuable in a broad range of scientific fields. However, the intrinsic propagation loss of these waves poses a fundamental problem to many potential applications. To overcome this drawback, researchers have explored the possibility of loss compensation by means of surface plasmon–polarition amplification. Here we provide the first direct measurement of gain in propagating plasmons using the long-range surface plasmon–polariton supported by a symmetric metal stripe waveguide that incorporates optically pumped dye molecules in solution as the gain medium. The measured mode power gain is 8.55 dB mm−1. Furthermore, it is shown that this new class of amplifier benefits from reduced spontaneous emission into the amplified mode, potentially leading to low-noise optical amplification. Researchers overcome the propagation loss of surface-plasmon polaritons, with this demonstration being the first direct gain measurement of propagating plasmons. Low-loss long-range modes of a metal stripe waveguide are amplified by using optically pumped dye molecules in solution as the gain medium. The mode power gain was measured to be 8.55 dB mm−1.

Amplification of long-range surface plasmons by a dipolar gain medium

What are believed to be the first experimental observations of the existence of long-range plasmon–polariton waves, guided by a thin metal film of finite width, are presented. A waveguide composed of an 8-µm-wide, 20-nm-thick, 3.5-mm-long Au metal film embedded in SiO2 was successfully excited at a free-space wavelength of 1.55 µm in an end-fire experiment. The theoretical nature of the phenomenon is described, and experimental observations of field confinement provided by this metal waveguide are presented in detail.

Pierre Berini

Papers

Long-range surface plasmon polaritons

Plasmon-polariton waves guided by thin lossy metal films of finite width: Bound modes of asymmetric structures

Surface plasmon–polariton amplifiers and lasers

Amplification of long-range surface plasmons by a dipolar gain medium

Experimental observation of plasmon–polariton waves supported by a thin metal film of finite width