Search

A simple numerical method based on finite differences to solve the scalar wave equation encountered in optical fibers is presented. The method uses the Ricatti transformation to the scalar wave equation and is capable of analyzing fibers of arbitrary refractive index profiles. Achieving errors as low as 0.005% for propagation constants is possible for lower-order modes. However, the error seems to increase for frequencies closer to cutoff.

The effects of doping on the electrical and optical properties of RF-sputtered a-Si/sub x/Ge/sub 1-x/:H (x=0.70) are investigated. The films were deposited at a constant substrate temperature of 200 degrees C, and n and p-doped samples were obtained by introducing controlled amounts of phosphine and diborane, respectively, in the sputtering atmosphere. The conductivity increased by about two orders of magnitude for the n-type samples and by one order of magnitude for the p-type samples. Thermoelectric power measurements confirmed that doping was achieved. The optical gap did not seem to vary upon doping. The presence of germanium and oxygen is responsible for an increase of the localized states in the gap and of the width of the conduction band tail states. Therefore, these films show less sensitivity to doping than those of a-Si:H deposited under similar conditions. A model for the density of states in the gap, which includes the effects of impurities (oxygen), , is presented in order to explain the observed results. >

Amorphous thin films of Si x Ge 1- x :H:O ( x = 0.70) were prepared by RF-sputtering at several substrate temperatures. The structural properties of these films were studied by IR spectroscopy and revealed features characteristic of hydrogen and/or oxygen bonded to silicon. The optical constants ( n, k ) were determined from reflection and transmission measurements at near-normal incidence for photon energies in the range of 1 and 2.6 eV. The optical gap was derived from the Tauc plot and correlated with the composition of the samples. The increase of hydrogen and/or oxygen decreases the value of refractive index and increases the optical gap. The room temperature DC conductivity can be reduced by as much as four orders of magnitude by combining the effects of hydrogen and oxygen compensation and for the concentrations used. The dependence of the conductivity on the atomic concentrations of hydrogen and/or oxygen follows a similar trend as the refractive index.

Samples of ZBLA and HBLA glasses were subjected to various fluences of neutron irradiation, and the spectral dependence of optical absorption was measured before and after irradiation. The IR edge was found to be unaffected by neutron irradiation for the fluences used. However, a red shift occurred at the UV edge which slightly recovered after three weeks.