For thin-fi lm solar cells, light absorption is usually proportional to the fi lm thickness. However, if freely propagating sunlight can be transformed into a guided mode, [ 1 ] the optical path length signifi cantly increases and results in enhanced light absorption within the cell. [ 2 ] We propose here a light absorber based on coupling from a periodic arrangement of resonant dielectric nanospheres. It is shown that whispering gallery modes in the spheres can be coupled into particular modes of the solar cell and signifi cantly enhance its effi ciency. We numerically demonstrate this enhancement using full-fi eld fi nite difference time-domain (FDTD) simulations of a nanosphere array above a typical thin-fi lm amorphous silicon (a-Si) solar cell structure. The in-coupling element in this design is advantageous over other schemes as it is composed of a lossless material, and its spherical symmetry naturally accepts large angles of incidence. Also, the array can be fabricated using simple, well-developed methods of self assembly and is easily scalable without the need for lithography or patterning. This concept can be easily extended to many other thin-fi lm solar cell materials to enhance photocurrent and angular sensitivity.Thin-fi lm photovoltaics offer the potential for a signifi cant cost reduction [ 3 ] compared to traditional, or fi rst generation, photovoltaics usually at the expense of high effi ciency. This is achieved mainly by the use of amorphous or polycrystalline optoelectronic materials for the active region of the device, for example, a-Si. The resulting carrier collection effi ciencies, operating voltages, and fi ll factors are typically lower than those for single-crystal cells, which reduce the overall cell effi ciency. There is thus great interest in using thinner active layers combined with advanced light trapping schemes to minimize these problems and maximize efficiency. A number of light trapping schemes have been proposed and demonstrated including the use of plasmonic gratings, [ 4 , 5 ] arrays of metal cavities that support void plasmons, [ 6 ] photonic crystals, [ 7 ] nano-and microwires, [ 8 , 9 ] nanodomes, [ 10 ] aggregates of nanocrystallites, [ 11 ] and dielectric diffractive structures. [ 12 ] A previous report [ 12 ] described the use of sub-wavelength dielectric spheres and other scattering mechanisms for enhancing light scattering and absorption. Here, we propose a new concept for light trapping in thin-fi lm solar cells through the use of wavelength-scale resonant dielectric nanospheres that support whispering gallery modes to enhance absorption and photocurrent.Wavelength-scale dielectric spheres [ 13 ] are interesting photonic elements because they can diffractively couple light from free space and also support confi ned resonant modes. Moreover, the periodic arrangement of nanospheres can lead to coupling between the spheres, resulting in mode splitting and rich bandstructure. [ 14 , 15 ] The coupling originates from whispering gallery modes (WGM) inside the spheres...

The spatial confinement of surface plasmon polaritons is a promising route for realizing optical on-board interconnects. However, mode losses increase with the confinement factor. To overcome this road block, we investigate propagation assisted by stimulated emission in a polymer strip-loaded plasmonic waveguide doped with nanocrystals. We achieve 27% increase of the propagation length at telecom wavelength corresponding to a 160 cm(-1) optical gain coefficient. Such a configuration is a step toward integrated plasmonic amplifiers.

The realization of practical on-chip plasmonic devices will require efficient coupling of light into and out of surface plasmon waveguides over short length scales. In this letter, we report on low insertion loss for polymer-on-gold dielectric-loaded plasmonic waveguides end-coupled to silicon-on-insulator waveguides with a coupling efficiency of 79 ± 2% per transition at telecommunication wavelengths. Propagation loss is determined independently of insertion loss by measuring the transmission through plasmonic waveguides of varying length, and we find a characteristic surface-plasmon propagation length of 51 ± 4 μm at a free-space wavelength of λ = 1550 nm. We also demonstrate efficient coupling to whispering-gallery modes in plasmonic ring resonators with an average bending-loss-limited quality factor of 180 ± 8.