Abstract
Long-period fiber gratings (LPGs) have been inscribed in nitrogen-doped fibers by electrical arc discharge. The influence of drawing tension as well as external load applied during arc discharge on coupling strength has been investigated. The influence of drawing tension on the grating's coupling strength is found to be negligible, whereas the coupling strength increases considerably with external load. Tomographic stress profiles of the fiber have been recorded before and after electric arc discharge. The axial stress modulation in the core region of the grating was found to be smaller than 10 MPa and is thus too small to be the dominating mechanism for grating formation.

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
The electric arc technique is used to apodize fiber Bragg gratings (FBGs). Arc discharges applied to the ends of the grating produce a smoothing of the refractive-index modulation profile reducing the sidelobes of the reflection spectrum at longer wavelengths. A sidelobe reduction of 17 dB was obtained. (c) 2007 Wiley Periodicals, Inc.

Abstract
Long-period gratings were written in a pure-silica-core fiber using the electric arc technique. To assess the influence of stress relaxation on grating formation, tomographic stress measurements were performed inside the grating. No stress annealing could be observed within the accuracy of the stress measurement, suggesting a negligible photo-elastic contribution to the arc-induced perturbation of the index profile. In contrast, stress relaxation was found inside a splice of pure-silica-core fiber where discharge conditions are different, indicating the general potential to alter the fibers stress and thus the index profile using an electric arc.

Abstract
Fiber Bragg grating (FBG) arrays in pure silica four-leaf-clover-shaped suspended core fibers were inscribed with two-beam interference and a deep UV femtosecond laser source. The target fibers are pure silica and do not contain any dopants, nor were they treated with hydrogen before grating inscription. The inscription method is appropriate to measure the effective mode field index of the fiber and allows confinement factors of the guided modes to be derived. Applications of such FBGs can be expected especially for fiber sensing.

Abstract
Cyanobacteria deteriorate the water quality and are responsible for emerging outbreaks and epidemics causing harmful diseases in Humans and animals because of their toxins. Microcystin-LR (MCT) is one of the most relevant cyanotoxin, being the most widely studied hepatotoxin. For safety purposes, the World Health Organization recommends a maximum value of 1 mu g L(-1) of MCT in drinking water. Therefore, there is a great demand for remote and real-time sensing techniques to detect and quantify MCT. In this work a Fabry-Perot sensing probe based on an optical fibre tip coated with a MCT selective thin film is presented. The membranes were developed by imprinting MCT in a sol-gel matrix that was applied over the tip of the fibre by dip coating. The imprinting effect was obtained by curing the sol-gel membrane, prepared with (3-aminopropyl) trimethoxysilane (APTMS), diphenyl-dimethoxysilane (DPDMS), tetraethoxysilane (TEOS), in the presence of MCT. The imprinting effect was tested by preparing a similar membrane without template. In general, the fibre Fabry-Perot with a Molecular Imprinted Polymer (MIP) sensor showed low thermal effect, thus avoiding the need of temperature control in field applications. It presented a linear response to MCT concentration within 0.3-1.4 mu g L(-1) with a sensitivity of -12.4 +/- 0.7 nm L mu g(-1). The corresponding Non-Imprinted Polymer (NIP) displayed linear behaviour for the same MCT concentration range, but with much less sensitivity, of -5.9 +/- 0.2 nm L mu g(-1). The method shows excellent selectivity for MCT against other species co-existing with the analyte in environmental waters. It was successfully applied to the determination of MCT in contaminated samples. The main advantages of the proposed optical sensor include high sensitivity and specificity, low-cost, robustness, easy preparation and preservation.