Abstract
We report on the use of CHF3, C2F6, and SF6 as etch gases for deep reactive ion etch processing of germano-boro-silicate glass films prepared by flame hydrolysis deposition (FHD). The glass film under study had a composition of 83 wt % SiO2, 12 wt % GeO2, and 5 wt % B2O3. The scope of the study was to identify the benefits and drawbacks of each gas for fabrication of deep structures (>10 mu m) and to develop an etch process in each peas system. The etch rate, etch profile, and surface roughness of the FHD glass films were investigated for each gas. Etch rates and surface roughness were measured using a surface profiler and etch profiles were assessed using a scanning electron microscope. It was found that SF6 had the highest FHD glass etch rate and nichrome mask selectivity (>100:1) however, it had the lowest photoresist mask selectivity (<1:2) and highest lateral erosion. CHF3 had the lowest FHD glass etch rate but high selectivity over both nichrome (>80:1) and photoresist (>10:1) and the etch profile was found to be smooth and vertical. C2F6 had a similar etch profile to that of CHF3, but the selectivity over both mask materials was lower than in CHF3. Fused silica was used as a reference material where it was found the percentage drop in etch rate in C2F6, SF6, and CHF3 was -12%, -15%, and -37%, respectively. From the results presented here CHF3 proved to be the most versatile etch process as either photoresist or nichrome masks could be used to attain depths of 20 mu m, or more. (C) 1998 American Vacuum Society.

Abstract
Fluorescence lifetimes and scatter losses for Er3+ doped, silica waveguides formed by aerosol doping and flame hydrolysis deposition are reported. The fast decay component and out of plane scatter decreased markedly with optimisation of the deposition technique, sintering process and co-doping regime. (C) 1998 Elsevier Science B.V.

Abstract
The simultaneous production of both a 2-D waveguide and a Bragg grating is reported. The samples used consisted of a three layer slab structure produced by flame hydrolysis deposition. They were exposed to a focused KrF excimer laser beam. The exposure was done through a non-absorbing quartz plate which contained a 6 mm long phase mask with a period of 1066 nm on its central part. A type II grating was obtained, with the periodic perturbation clearly observed under a microscope.

Abstract
Propagation of short laser pulses in gases resulting in relativistic ionization fronts is studied numerically using a kinetic formulation based in the photon number phase-space distribution function. With this approach we are able to follow the dynamics of the laser pulse both in time and spectral content. The advance of the photon number is obtained by solving a Klimontovich type equation. The properties of the emergent laser pulse, responsible for the ionization front, such as duration, chirp and spectrum are continuously monitored by adequate diagnostics of the photon number phase-space distribution. In particular, a detailed analysis of the evolution of the laser pulse velocity is presented.

Abstract
The growth dynamics of UV induced IR absorption and related refractive index change in hydrogen loaded GeO2-doped fibers have been studied. We report a higher initial rate and strong saturation for Ge-OH generation compared with Si-OH formation under UV exposure. A close correlation was found between the Ge/Si-OH groups concentration and the induced index change as a function of the UV exposure time. (C) 1998 American Institute of Physics.

Abstract
A systematic investigation of erbium diffusion in lithium niobate (LiNbO3) crystal as a function of crystal cut-direction, diffusion process parameters (temperature and time), and initial film thickness is reported. Depth concentration profiles of erbium are obtained by secondary ion mass spectrometry (SIMS). Combining experimental data with diffusion theory, the relevant diffusion parameters are derived. Diffusion from an infinite source of erbium ions is studied to evaluate the solid solubility lower limit of Er in LiNbO3. A thin film diffusion regime, with complete depletion of ion source. is also investigated. A comparison of Er diffusion with Er/Ti codiffusion in LiNbO3 crystals is reported.