Research interest in ZnO nanostructures derives from their excellent luminescent properties and availability of low cost fabricating and processing,which hold promise for the development of electronic and optoelectronic nanodevices.In this review,we focus on the progress in synthesis,properties and nanodevices of ZnO nanorod(NR)arrays and nanotetrapods(NTPs).Recent work done by the authors are also presented.After a brief introduction to the controlled fabrication methods for the highly-ordered ZnO NR arrays and NTPs,we present some aspects of the fundamental properties,especially optical performance,of ZnO NRs/NTPs.Then,we provide an overview of the applications to functional nanodevices based on individual NR and NTP of ZnO.It is demonstrated that different morphologies of ZnO nanostructures have salient effects on their properties and applications.Although much progress has been achieved in the fundamental and applied investigations of ZnO NRs/NTPs over the past decade,many obstacles still remain,hampering further development in this field.Finally,some longstanding problems that warrant further investigation are addressed.
By employing 2D plane wave expansion (PWE) and finite difference time domain (FDTD) methods,a photonic crystal waveguide (PCW) based on the compound square lattice structure is presented. Band-gap can be observed for TM polarization and compared with the simple lattice structure based on the same material,the band-gap is increased by 62.7%. Byoptimizing the parameters we get the PCW with the propagation only near the wavelength of 1.55 μm and a flat group indexcurve in a wide wavelength range of 40 nm. And the group velocity dispersion compensation can be realized by thestructure optimization. The results provide a reference for the study and application of photonic crystal waveguide based on the compound lattice structure.
A slotted single-mode photonic crystal waveguide with a linear tapered slot is presented to realize slow light,whose dispersion curve is shifted by changing the slot width.When the slot width is reduced,the band curve shifts in the tapered structure,and the group velocity of light approach zero at the cut-off frequency.Therefore,different frequency components of the guided light are slowed down even localized along the propagation direction inside a tapered slot photonic crystal waveguide.Furthermore,this structure can confine slow light-wave in a narrow slot waveguide,which may effectively enhance the interaction between slow light and the low-index wave-guiding materials filled in the slot.In addition,this tapered slot structure can be used to compensate group velocity dispersion of slow light by modifying the structure,thus opening the opportunity for ultra-wide bandwidth slow light.
WU Jun LI YanPing YANG ChuanChuan PENG Chao WANG ZiYu
