Wang Daobin

Full-vector improved effective index method for analysis of fiber Bragg gratings formed in photonic crystal fibers

The reflectivity and the Bragg wavelength of a fiber Bragg grating formed in a photonic crystal fiber with central pure core defect and a regular hexagonal array of microscopical holes cladding were investigated by the full vector improved effective index method, the calculated results indicate that the effective index of the FSFM decreases with increasing the filling factor, the reflectivity increases with the filling factor increasing, the Bragg wavelength decreases from 1544.133 nm to 1540.509 nm with the filling factor increasing.

Study on dispersion of optical fiber with cladding made of uniaxial crystal materials

The dispersion of the fiber with cladding made of uniaxial anisotropic crystal material with optical axis running along its length was investigated by means of numeric solution. The calculated results indicate that the parameter Kd has a strong impact on the dispersion and the zero dispersion wavelength of this kind of fiber, and the zero dispersion wavelength decreases with Kd increasing These studies provide an important basis for designing different zero dispersion fiber and for electric field or strain sensing.

Structures and electronic properties of SimN8-m(0 < m < 8) clusters: a density functional theory study

The geometries, electronic structures and related properties of SimN8-m(0 < m < 8) clusters are studied using density functional theory (DFT) with hybrid functional B3LYP. The calculated results reveal several trends. For any stoichiometric clusters, the lowest energy isomers with an alteration of N and Si atoms are favourable in energy if the numbers of Si and N atoms are large enough to form ... Si–N–Si–N... alternative chains. The bond lengths of single Si–N bonds are very close to the corresponding values of the bulk and other Si–N clusters. The geometries for N-rich and Si4N4 clusters are planar structures, but three-dimensional structures are favourable in energy for Si-rich clusters. With the increase of m, the isotropic polarizability and average polarizability increase, the total binding energies generally decrease, the HOMO-LUMO gap and vertical ionization potential oscillate with increasing number of valence electrons, and their values with even valence electrons are larger than those with odd valence electrons. The atomic charges, IR and Raman properties are also reported.

Effect of a magnetic field on the energy levels of donor impurities in the ZnO parabolic quantum well

Energy levels of a donor impurity in the ZnO parabolic quantum well under the magnetic field are investigated using the variational method. The binding energy of the ground state, the energies of 2p± state and 1s ! 2p transition energies of a hydrogenic donor in the ZnO parabolic quantum well are numerically calculated as a function of the strength of magnetic field for different parabolic potential fields. The results show that the external magnetic field has an obvious influence on the binding energies and the 1s ! 2p transition energies of a hydrogenic donor. The 1s to 2p transition energy increases linearly with the strength of magnetic field, but the 1s to 2p transition energy decreases when the strength of magnetic field increases for the small field strength. Compared to the GaAs parabolic well, the donors are more tightly bound to the ZnO parabolic well and the influence of external magnetic field on the binding energy of a donor is much stronger in the ZnO parabolic well.