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.

Abstract
A pseudoheterodyne, open-loop demodulation technique? for detecting wavelength shifts in wavelength encoded fiber Bragg grating sensors is presented, The scheme uses a processing Bragg grating that is identical to one used as a sensor, When the processing fiber grating is stretched periodically, the system of two gratings produces a carrier at this frequency with its phase modulated by the measurand signal applied to the sensing grating, The demodulation technique is intrinsically immune to fluctuation of optical power in the system and is independent of the source spectral profile characteristics. A resolution of approximate to 1 mu epsilon/root Hz for static axial strain was achieved.

Abstract
A passive all-fibre technique for fibre Bragg grating wavelength shift detection which has been discussed previously is used here for the demodulation of two Bragg sensors placed in a tree topology and addressed in time. The scheme involves a light source with a particular spectral profile that allows the direct tracking of the Bragg wavelength shifts, providing satisfactory resolution over a large dynamic range and a direct application in demultiplexing fibre sensing systems. Experimental results are presented relative to the measurement of static and dynamic strain, as well as temperature.