Abstract
The symmetry of cladding modes excited in microbend and arc-induced long-period fiber gratings is investigated. An optimization technique is developed to determine the fiber parameters and to associate grating resonances with cladding modes of a particular symmetry. Using this optimization procedure, we show that the gratings induced in a standard fiber by arc discharges and microbends couple light to the antisymmetric cladding modes. In the case of a boron-germanium codoped fiber, the cladding modes excited by arc-induced gratings are found to be symmetric. Measurements of the near-field intensity distribution of cladding modes confirm the mode symmetry ascertained by the optimization technique. (c) 2006 Optical Society of America

Abstract
Long-period gratings were written using arc discharges in pristine nitrogen doped fibres. Comparison of the resulting gratings spectra show that the resonant positions of gratings in fibres pre-annealed at 1050 degrees C for 30 min are shifted towards shorter wavelengths and their coupling strength is considerably higher. The refractive index and residual stress profiles were measured before and after annealing, as well as the two-dimensional stress profiles inside the grating region. Arc discharges induce periodic and strong asymmetric stresses in the fibre core of the pre-annealed nitrogen doped fibre.

Abstract
By measuring intensity distributions of cladding modes and using an optimization technique we show that the perturbation which forms arc-induced gratings in standard fibers is antisymmetric, while the perturbation in boron-germanium codoped fibers is symmetric. © 2006 Optical Society of America.

Abstract
The fabrication and characterization of long-period gratings (LPGs) in fiber tapers is presented alongside supporting theory. The devices possess a high sensitivity to the index of aqueous solutions due to an observed spectral bifurcation effect, yielding a limiting index resolution of +/- 8.5 x 10(-5) for solutions with an index in the range 1.330-1.335.

Abstract

Abstract
A versatile time-domain OCT system is presented which, for the first time, can generate cross-section images (B-scans) by using either transverse priority (T-scans) or depth priority (A-scans). Images from the optic nerve are obtained with either regime, with the same system. In different scanning regimes, different values are allowed for the maximum power to be launched to the eye. We present the maximum exposure level for a variety of scanning procedures, such as generation of cross section images and 3D volumes employing either A or T scanning.