Strong Localization of Surface Plasmon Polaritons with Engineered Disorder.

In this work, we experimentally demonstrate for the first time strong localization of surface plasmon polaritons (SPPs) at visible regime in metallic nanogratings with short-range correlated disorder. By increasing the degree of disorder, the confinement of SPPs is significantly enhanced, and the effective SPP propagation length dramatically shrinks. Strong localization of SPPs eventually emerges at visible regime, which is verified by the exponentially decayed fields and the vanishing autocorrelation function of the SPPs. Physically, the short-range correlated disorder induces strong interference among multiple scattered SPPs and provides an adequate fluctuation to effective permittivity, which leads to the localization effect. Our study demonstrates a unique opportunity for disorder engineering to manipulate light on nanoscale and may achieve various applications in random nanolasing, solar energy, and strong light-matter interactions.

Freely tunable broadband polarization rotator for terahertz waves.

A freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging.

Band modulation and in-plane propagation of surface plasmons in composite nanostructures.

In this work, we have experimentally and theoretically studied band modulation and in-plane propagation of surface plasmons (SPs) in composite nanostructures with aperture arrays and metallic gratings. It is shown that the plasmonic band structure of the composite system can be significantly modulated because of coupling between the aperture and grating. By changing the relative positions between these optical components, the resonant modes would shift or split. And the resonant SP modes launched on the structure surface can be effectively modified by the geometric parameters. Further, we provide an experimental observation to directly show the SP in-plane propagation by using far-field measurements, which agree with the simulated results. Our study offers a convenient way for observing the SP propagation in far field, and provides unique composite nanostructures for possible applications in subwavelength optodevices, such as optical sensors and detectors.

Dual-mode electromagnetically induced transparency and slow light in a terahertz metamaterial.

In this Letter, we construct a metamaterial with dual-mode electromagnetically induced transparency (EIT)-like behavior by introducing "bright atoms," "quasi-dark atoms," and "dark atoms" simultaneously. The dual-mode EIT-like behavior has been demonstrated both experimentally and theoretically in terahertz (THz) regime. At two EIT-like modes, slow light is also observed as two time-delayed wave packets, and the effective group refractive index can reach 10(2). Furthermore, stable dual-mode EIT-like behavior is verified in this metamaterial for a wide range of oblique incident angles. Our work provides a design approach to mimic dual-mode EIT, and such an approach may achieve potential applications on miniaturized and versatile THz devices.

Position-sensitive spectral splitting with a plasmonic nanowire on silicon chip.

On-chip nanophotonics serves as the foundation for the new generation of information technology, but it is challenged by the diffraction limit of light. With the capabilities of confining light into (deep) subwavelength volumes, plasmonics makes it possible to dramatically miniaturize optical devices so as to integrate them into silicon chips. Here we demonstrate that by cascading nano-corrugation gratings with different periodicities on silver nanowires atop silicon, different colors can be spatially separated and chronologically released at different grating junctions. The released light frequency depends on the grating arrangement and corrugation periodicities. Hence the nanowire acts as a spectral splitter for sorting/demultiplexing photons at different nano-scale positions with a ten-femtosecond-level interval. Such nanowires can be constructed further into compact 2D networks or circuits. We believe that this study provides a new and promising approach for realizing spatiotemporal-sensitive spectral splitting and optical signal processing on nanoscales, and for general integration of nanophotonics with microelectronics.

Tunable multimode and narrowband in a photonic quasicrystal waveguide.

In this work, we propose a photonic quasicrystal waveguide, which contains a hollow core surrounded by coaxial dielectric quasiperiodic multilayer. Due to the self-similarity in the cladding structure, multiple omnidirectional photonic band gaps (PBGs) exist in the waveguide. The light waves with the frequencies within the omnidirectional PBGs are totally reflected, thereafter, the transport of multimodes is achieved in the quasiperiodic waveguide. Further, it is shown that the centre frequency and the width of the omnidirectional PBG can be tuned by the refractive indexes or the generations of the quasiperiodic sequence in the cladding multilayer. As a consequence, both the quality factor and the confinement performance of the waveguide can be significantly enhanced by decreasing the width of the omnidirectional PBGs. The investigations make it possible to design miniaturized multifunctional optical devices, such as on-chip narrowband waveguide-based filters and laser resonators.