Extraordinary characteristics for one-dimensional parity-time-symmetric periodic ring optical waveguide networks

In this paper, we design a one-dimensional(1D) parity-time-symmetric periodic ring optical waveguide network(PTSPROWN) and investigate its extraordinary optical characteristics. It is found that quite different from traditional vacuum/dielectric optical waveguide networks, 1D PTSPROWN cannot produce a photonic ordinary propagation mode, but can generate simultaneously two kinds of photonic nonpropagation modes: attenuation propagation mode and gain propagation mode. It creates neither passband nor stopband and possesses no photonic band structure. This makes 1D PTSPROWN possess richer spontaneous PT-symmetric breaking points and causes interesting extremum spontaneous PT-symmetric breaking points to appear, where electromagnetic waves can create ultrastrong extraordinary transmission, reflection, and localization, and the maximum can arrive at 6.6556 × 10^(12) and is more than 7 orders of magnitude larger than the results reported previously.1D PTSPROWN may possess potential in designing high-efficiency optical energy saver devices, optical amplifiers, optical switches with ultrahigh monochromaticity, and so on.

Fabrication and near-infrared optical responses of 2D periodical Au/ITO nanocomposite arrays

Two-dimensional(2D) periodical Au and indium tin oxide(ITO) nanocomposite arrays have been fabricated based on a self-assembled nanosphere lithography technique. A button-shaped Au nanoparticle was formed on each hollow hemisphere-shaped ITO shell. Importantly, the underlying formation mechanism during the thermal treatment has been thoroughly explored by comparing structures resulting from different deposition conditions in detail. Compared to the Au nanoparticle arrays without ITO shells, the Au/ITO nanocomposite arrays showed a stronger localized surface plasmon resonance effect and higher absorption in the near-infrared(NIR) region, benefiting from the free-electron interaction enhancement between Au and ITO. The nonlinear optical properties were investigated using a modified femtosecond intensity-scan system, and the results demonstrated Au/ITO nanocomposite arrays with a remarkable two-photon absorption saturation effect for femtosecond pulses at 1030 nm. The versatile NIR optical responses indicate the great potential of the elaborately prepared 2D periodical Au/ITO nanocomposite arrays in many applications such as solar cells, photocatalysis,and novel nano optoelectronic devices.