Abstract
We compare the thermal tuning capabilities of two type I gratings written in unloaded and in hydrogen-loaded germanium-doped silica fibers, and a type IIa grating written in unloaded fiber. The hydrogen-loaded grating is annealed after writing, to remove any unreacted hydrogen. We further study the gratings' response stability with temperature, an important property when these devices are used as optical filters in wavelength division multiplexing systems. Experimental results show that the worst option is the type I grating in unloaded fiber, which presents the highest bandwidth and group delay variations with temperature, so that it is the least suitable as a thermotunable optical filter in wavelength-multiplexed systems. For the other two options, the bandwidth and group delay variations are much smaller, the lowest values being obtained with the hydrogen-loaded type I grating, and the best thermal tuning efficiency with the type IIa grating. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Abstract
Bragg gratings written in high-birefringence fibre optics are a key element in the simultaneous measurement of transversal strain components and temperature, and they have several applications as single polarisation optical filters for wavelength division multiplexing (WDM) applications. Precise determination of grating characteristics is needed to aid device design, particularly taking into account the polarisation of the illuminating light. The authors report results concerning the production and characterisation of Bragg gratings in high birefringence fibre. Birefringence is measured by the wavelength dependence of the beat length, and from the Bragg grating reflection bands, for three common high birefringence fibres. Characterisation of the gratings when subjected to transversal strain and temperature is described, as well as results of the use of the grating to measure, simultaneously, those two parameters.

Abstract
In this contribution we compare the thermal stability of type I and type IIa gratings written in germanosilicate fibers. We study and compare their central wavelengths drifts and variations of the maximum reflectivity with temperature. Also, two other important factors, the bandwidth and group delay characteristics are characterized, compared, and the differences justified, based on the gratings physical structure.

Abstract
Fiber Bragg grating (FBG) written in normal and reduced diameter high birefringence (HiBi) optical fibers have been studied. Chemical etching is used to reduce the fiber diameter while the optical properties of the FBG spectrum are measured. The obtained results agree qualitatively with the stress enhanced chemical etching. They also permit to determine the birefringence of the fiber as a function of the diameter. Optical characterization of the FBG under transversal strain and temperature is performed. The obtained results permit the simultaneous measurement of those parameters with a HiBi FBG sensor.

Abstract
In this paper we report the implementation of fiber Bragg gratings with variable negative mean refractive index perturbation, in a highly germanium-doped fiber, resultant from a type IIa exposition regime. The obtained grating presents a favorable group delay characteristic for dispersion compensation applications with reduced bandwidth.

Abstract
We propose and demonstrate an architecture of a 2 x 2 port optical cross-connect (OXC) using tuneable fibre Bragg gratings and optical circulators. The proposed OXC is scalable to N x N ports owing to the cascadability of individual routing modules, which perform routing of specific wavelength channels. The performance of the cross-connect is also experimentally evaluated.