Guofeng Song

Design of plasmonic back structures for efficiency enhancement of thin-film amorphous Si solar cells

Metallic back structures with one-dimensional periodic nanoridges attached to a thin-film amorphous Si (a-Si) solar cell are numerically studied. At the interfaces between a-Si and metal materials, the excitation of surface-plasmon polaritons leads to obvious absorption enhancements in a wide near-IR range for different ridge shapes and periods. The highest enhancement factor of the cell external quantum efficiency is estimated to be 3.32. The optimized structure can achieve an increase of 17.12% in the cell efficiency.

Plasmonic surface-wave splitter

The authors present an analysis of a plasmonic surface-wave splitter, simulated using a two-dimensional finite-difference time-domain technique. A single subwavelength slit is employed as a high-intensity nanoscale excitation source for plasmonic surface waves, resulting in a miniaturized light-surface plasmon coupler. With different surface structures located on the two sides of the slit, the device is able to confine and guide light waves of different wavelengths in opposite directions. Within the 15 mu m simulation region, it is found that the intensity of the guided light at the interface is roughly two to eight times the peak intensity of the incident light, and the propagation length can reach approximately 42 and 16 mu m and at the wavelengths of 0.63 and 1.33 mu m, respectively. (c) 2007 American Institute of Physics.

Observation of ultra-narrow band plasmon induced transparency based on large-area hybrid plasmon-waveguide systems

We report the observation of an ultra-narrow band plasmon induced transparency resonance which is realized in a large area hybrid plasmon-waveguide system consisting of a gold nanowire array embedded in a slab waveguide. Due to the destructive interference between optical modes supported by the hybrid system, an ultra-narrow plasmon induced transparency resonance with a bandwidth of 8 nm at the wavelength of 966 nm was obtained (i.e., ∼1/120 of the peak wavelength at the incident angle of 60°). The group velocity is estimated to be ∼76, which is promising for miniaturized slow-light components.

Hybrid plasmonic waveguide with gain medium for lossless propagation with nanoscale confinement

In this Letter, we propose a hybrid plasmonic nanosystem consisting of a silver cladding layer with a semicylinder bump on top of InGaAsP nanowire. Because of the coupling between the dielectric waveguide mode and surface plasmon polariton mode, the hybrid plasmonic mode can exhibit low loss with strong field localization. The finite element method numerical simulations are employed to evaluate the performances of the hybrid mode. In order to achieve the lossless propagation of the hybrid mode with the mode area of 0.0058(λ²/4) at 1.55 μm, the material gain of 200 nm × 300 nm InGaAsP nanowire should reach 1223 cm⁻¹.

Slow light at terahertz frequencies in surface plasmon polariton assisted grating waveguide

A subwavelength grating waveguide (GW) consisting of two parallel metallic slabs with periodic corrugations on their inner boundaries is developed to slow down the speed of light at terahertz frequencies. Assisted by a tapered input port, our structure has a transfer efficiency of about 80% over a broad bandwidth and strong confinement in the subwavelength scale. Based on the GW, three graded GWs are designed to demonstrate that the spoof surface plasmon polaritons are slowed down and asymptotically stopped when they tend to the location, where the local cutoff frequency is the same as the frequency of the incident light.

Plasmonic very-small-aperture lasers

The fabrication of plasmonic very-small-aperture lasers is demonstrated in this letter. It is an integration of the surface plasmon structures and very-small-aperture lasers (VSAL). The experimental and numerical results demonstrate that the transmission field can be confined to a spot with subwavelength width in the far field, and the power output can be enhanced 140% of the normal VSAL. Such a device can be useful in the application of a high resolution far-field scanning optical microscope.

Double Plasmon-Induced Transparency in Hybrid Waveguide-Plasmon System and Its Application for Localized Plasmon Resonance Sensing with High Figure of Merit

We demonstrate multispectral sharp plasmon-induced transparency response in a hybrid waveguide-plasmon system. By using the classical mechanical model of coupled damped harmonic oscillators, a clear and intuitive interpretation of the construction of the double-electromagnetically induced transparency (EIT)-like phenomenon is provided. High figure of merit up to 28.8 of the system for localized plasmon resonance refractive index sensing is obtained. Narrow polarization-independent double EIT-like spectral response is constructed, which provides an efficient tool for possible applications on slow light, enhanced nonlinear effect, nanoplasmonic functional devices, and integrated optical circuit.

Omnidirectional absorption enhancement in hybrid waveguide-plasmon system

We investigate the omnidirectional absorption enhancement induced by the excitation of the localized surface plasmon in the hybrid system consisting of a gold nanowire array embedded in a slab waveguide. Assisted by the waveguide layer, the hybrid system can support the localized waveguide-plasmon resonances for a wide range of incident angles. Theoretical and experimental results are both presented to demonstrate the omnidirectional absorption enhancement which could find important applications on plasmonic-assisted photovoltaic devices or photodetectors.

Slow Surface Plasmons in Plasmonic Grating Waveguide

A metal/air/metal (MAM) plasmonic grating waveguide (PGW) consisting of two parallel silver slabs with periodic corrugations on their inner boundaries is developed to slow down the group velocity of surface plasmon polaritons (SPPs) excited at near-infrared frequencies. For a Gaussian pulse excitation with the full width at half maxim (FWHM) of 222 fs and the center wavelength of 1.58 μm, the group velocity of 0.034c and the group velocity dispersion (GVD) of 0.8 ps/mm/nm can be achieved in finite-difference time-domain (FDTD) simulations with pulse excitation. Furthermore, a chirped PGW with varying groove depth is also demonstrated as a way to trap light by adopting continuous excitation.

Hybrid waveguide-plasmon resonances in gold pillar arrays on top of a dielectric waveguide.

We propose a hybrid waveguide-plasmon system consisting of gold pillar arrays on top of a dielectric waveguide. The formation of extraordinary transmissions induced by the hybrid waveguide-plasmon resonances is investigated by rigorous coupled-wave analysis. The characteristics of the hybrid resonances can be predicted by introducing the photonic crystal slab theory. Extremely narrow absorption peaks and the electromagnetically induced transparency-like optical property are demonstrated in our hybrid system.