Z.Y. Zhong

Engineering ultra-flattened-dispersion photonic crystal fibers with uniform holes by rotations of inner rings

We present a novel method for engineering ultra-flattened-dispersion photonic crystal fibers with uniform air holes by rotations of inner air-hole rings around the fiber core. By choosing suitable rotation angles of each inner ring, theoretical results show that normal, anomalous, and nearly zero ultra-flattened-dispersion fibers in wide spectra ranges of interest can be obtained alternatively. Moreover, in our dispersion sensitive analysis, these types of fibers are robust to variations from optimal design parameters. The method is suitable for the accurate adjustment of fiber dispersion within a small range, which would be valuable for the fabrication of ultra-flattened-dispersion fibers and also have potential applications in wide-band high-speed optical communication systems.

Slow Light in Square-Lattice Chalcogenide Photonic Crystal Holey Fibers

Slow light in square-lattice chalcogenide photonic-crystal (PC) holey fibers with uniform longitude geometry are proposed and theoretically investigated. By using the planewave-expansion method, a largest normalized complete 2-D photonic bandgap (CPBG) width of about 7.4% is found in an optimized connected-rod square-lattice chalcogenide PC, and the CPBG remains open with a refractive-index contrast as low as 2.48:1. We then consider the PCs as cladding layers to form holey fibers, and group indices up to several hundreds are predicted.

Working Pressure Dependence of Structure and Optical Performance of Zinc Oxide Thin Films by Magnetron Sputtering

Zinc oxide (ZnO) thin films were grown by magnetron sputtering onto glass substrates employing a sintered ceramic target and pure argon gas. The influence of working pressure on structure and optical performance of the thin films were studied by the measurements of X-ray diffraction (XRD) patterns and optical transmission spectra. The optical energy gap of the ZnO thin film were calculated according to the Taucs law. The results demonstrate that all the ZnO thin films have preferred orientation along (002) direction. The working pressure affects not only the structure parameters such as lattice constant, strain and stress in the plane of the film, but also the optical transmittance and energy gap of the ZnO thin films. The ZnO thin film deposited at the working pressure of 0.5 Pa exhibits the maximum average visible transmittance of 86.6%, a compressive stress of 1.72×109 Pa, and an optical energy gap of 3.273 eV.

Preparation, structure and optical properties of transparent conducting gallium-doped zinc oxide thin films

Abstract Highly conductive gallium-doped zinc oxide (GZO) transparent thin films were deposited on glass substrates by RF magnetron sputtering. The deposited films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe and UV-Vis spectrophotometer, respectively. The effect of growth temperature on the structure and optoelectrical properties of the films was investigated. The results demonstrate that high quality GZO films oriented with their crystallographic c-axis perpendicular to the substrates are obtained. The structure and optoelectrical properties of the films are highly dependent on the growth temperature. It is found that with increasing growth temperature, the average visible transmittance of the deposited films is enhanced and the residual stress in the thin films is obviously relaxed. The GZO films deposited at the growth temperature of 400°C, which have the largest grain size (74.3 nm), the lowest electrical resistivity (1.31×10-3 Ω·cm) and the maximum figure of merit (1.46×1O-2Ω-1), exhibit the best optoelectrical properties. Furthermore, the optical properties of the deposited films were determined by the optical characterization methods and the optical energy-gaps were evaluated by extrapolation method. A blue shift of the optical energy gap is observed with an increase in the growth temperature.

Absorption Enhancement in Thin-Film Amorphous Silicon Solar Cells by Symmetric Sub-Structure Binary Gratings

Absorption enhancement in thin-film amorphous silicon solar cells with symmetric sub-structure binary gratings is investigated by rigorous coupled wave analysis, and up to 1.77 times absorption is obtained in a preliminary optimized structure.

Effect of Argon Gas Pressure on Optical Properties of Zinc Oxide Thin Films Deposited by RF Magnetron Sputtering Technique

Zinc oxide (ZnO) thin films were deposited by radio frequency (RF) magnetron sputtering technique on glass substrates in pure argon gas. The optical transmission stectra of the films were measured by ultraviolet-visible spectrophotometer. The effects of argon gas pressure on optical properties of the deposited films were investigated. The optical band-gap of the films was evaluated in terms of the Taucs law. The results show that the argon gas pressure has slightly affected the optical band-gap of the deposited films. Furthermore, the refractive index and extinction coefficient of the films were determined by means of the optical characterization methods. Meanwhile, the dispersion behavior of the refractive index was studied by the single-oscillator model of Wemple and DiDomenico, and the physical parameters of the average oscillator strength, average oscillator wavelength, oscillator energy, the refractive index dispersion parameter and the dispersion energy were obtained.

Preparation and Microstructural Properties of Gallium Doped Zinc Oxide Thin Films for Organic Solar Cells

Transparent conducting gallium doped zinc oxide (GaZnO) films were prepared by magnetron sputtering technique. The influence of growth temperature on the microstructural and optical properties of the films were investigated by means of X-ray diffraction (XRD), spectrophotometer and optical characterization method, respectively. The results show that all the samples are polycrystalline in nature having a hexagonal wurtzite type crystal structure with a preferred grain orientation in the (002) direction. The growth temperature significantly affects the crystal structure and optical properties of the samples. The film deposited at the growth temperature of 670 K possesses the largest grain grain, the minimum dislocation density and the lowest microstrain. The average visible transmittance and optical energy gap of the samples increase gradually with the increment of growth temperature.

Study on Structural Properties of Gallium and Titanium Doped Zinc Oxide Films Deposited by Magnetron Sputtering

Thin films of transparent conducting gallium and titanium doped zinc oxide (GTZO) were prepared on glass substrates by magnetron sputtering technique using a sintered ceramic target. The microstructural properties of the deposited thin films were characterized with X-ray diffraction (XRD). The results demonstrated that the polycrystalline GTZO thin films consist of the hexagonal crystal structures with c-axis as the preferred growth orientation normal to the substrate, and that the working pressure significantly affects the crystal structures of the thin films. The GTZO thin film deposited at the working pressure of 0.4 Pa has the best crystallinity, the largest grain size and the lowest stress.

Wideband slow light in one-dimensional chirped silicon grating waveguide with round-corners

One-dimensional chirped silicon grating waveguide with round-corners has been designed to obtain wideband slow light. Wide bandwidth up to 9.6-nm slow light with group index of 40.7 can be obtained in an optimized waveguide.

Investigation of Optical Properties of Aluminium Doped Zinc Oxide Thin Films Deposited by Magnetron Sputtering

Aluminium doped zinc oxide (AZO) thin films were prepared by magnetron-sputtering. The optical and structural properties of the films were investigated by optical transmission spectra and X-ray diffraction (XRD) measurements, respectively. The results indicate that the AZO films have hexagonal wurtzite structure with highly c-axis preferred orientation. The optical and structural properties of the films are observed to be subjected to the argon pressure. The AZO film prepared at the argon pressure of 0.5 Pa exhibits the largest crystallite size and the highest average visible transmittance. Also, the refractive index and optical energy-gap of the films were determined by optical characterization methods. The dispersion behavior of the refractive index was studied using the Sellmeier’s dispersion model.