Abstract

Abstract
This paper reports a technical assessment of an all-optical 4×10 Gbps clock extraction technique in the context of fiber optic digital communication systems. The technique consists in putting a 1320 nm semiconductor laser in a self pulsating mode through injection locking to a CW source. The pulsations are triggered by a fast drive current step. The useful self pulsation region has been explored after extensive simulation providing a valuable knowledge for on-going experiments. Actual synchronization with optical data stream was observed both considering all ones and pseudo-random sequences. Phase sustaining of the clock over moderate-length sequences of zeros was noticed as the most encouraging result of this work.

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.