**1. Introduction**

Plasmonics has the fascinating ability to localize and guide light wave at the deep subwavelength scale, becomes an inter-discipline merging photonics with electronics [1–6]. Surface plasmons are free electron oscillations induced by optical methods at the metal surfaces. Both localized and propagated surface plasmons excited in metal nanoparticles and nanowires are of great interest. They not only break the diffraction limit but also allow

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

to guide light in various geometries such as 90° bending [1]. This promises the scaling of optical devices down to the diffraction limit for miniaturized photonic circuits. The localized surface plasmons have the functionality to scatter, absorb and squeeze light into nanometer scale, providing large enhancements of local near-fields [7]. It holds the potential applications in data storage, light energy generation, sub-wavelength optics, nano-optical tweezers, biophotonics and nanoscopy [8–11]. Gold nanoparticles with sphere/rod shapes and size below 100 nm are highly investigated for many useful applications, such as non/radiative enhancement of nano-crystals [12], inter-particle coupling effect [13], single particle plasmon spectroscopy [14–16], plasmonic sensing [17–19], plasmonic photocatalysis [20–22], and so on. Different from the localized surface plasmons of individual nanoparticles, the propagated surface plasmons existing at flat/curved surfaces in metallic planes, films, and wires also exhibit intriguing plasmonic phenomena [23]. The propagation length of surface plasmon modes is inevitably limited by metallic absorption, could also be strongly confined in the lateral section normal to propagation direction. This implies that plasmonic waveguides could transport larger bandwidth of information than that of conventional photonic waveguides. However, there is a trade-off between propagation loss and mode confinement in plasmonic waveguides [24]. To balance this trade off, an alternative method by seamlessly integrating photonic waveguides into plasmonic waveguides can be used [25]. Silver nanowires usually act as plasmonic waveguides with lateral size of 200−300 nm and axial length up to 10 μm, exhibiting many interesting applications. For example, plasmonic interference [26], waveparticle duality [27], remote excitation of Raman scattering [28–30], long-distance plasmonic gain [31–33], broadside nano-antennas [34], etc. It is impossible to introduce every result on plasmonics in this short chapter. In the following sections, we will specifically describe some novel results with gold nanorods/nanospheres and silver nanowires for achieving optical energy generation, propagation, and conversion.
