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We have studied the gamma-radiation induced effect on the Bragg peak position in fiber gratings. For the first time, to the best of our knowledge, a short-wavelength shift was observed for the Type I gratings written in an intrinsically photosensitive fiber. Based on the kinetics of the peak shift observed under irradiation and during post-irradiation annealing, we propose that two different types of defects are generated by ionizing radiation. One type is responsible for the refractive index increase during irradiation, while the creation of the defects of another type results in the index decrease. The concurrence of the two types of defects can be a way to obtain high stability of the gratings under irradiation. [ABSTRACT FROM AUTHOR]

In this paper, we present an experimental analysis of the effects induced in the transmitted spectrum by depositing a uniform high refractive index (HRI) thin coating on weakly tilted fiber Bragg gratings (TFBGs). Experiments were conducted on two weakly TFBGs presenting different tilt angles (5deg and 7deg) covered by two different coating thicknesses using the dip-coating technique. The transmission spectra of the obtained structures were collected as the surrounding refractive index (SRI) changed in the range 1-1.47. The coated gratings present some interesting differences in their spectral evolution in comparison to bare gratings. An important effect of HRI coatings is indeed to enhance the SRI sensitivity of the spectral position of the dips corresponding to cladding modes couplings, leading to an improvement of the efficiency of previous demodulation techniques exploited in the case of bare TFBGs. [ABSTRACT FROM PUBLISHER]

In this letter, a novel demodulation technique based on the monitoring of the polarization-dependent loss in a 1-nm wavelength range is proposed to measure the surrounding refractive index by means of weakly tilted fiber Bragg gratings. A 110-3 refractive index resolution as well as a temperature-insensitive behaviour are reported. [ABSTRACT FROM PUBLISHER]

This work reports on the experimental investigation of the spectral effects induced by uniform high refractive index nano-coatings deposited on weakly tilted fiber Bragg gratings (TFBGs). To this aim, weakly TFBGs with different tilt angles were fabricated and then coated with thin overlays of syndiotactic polystyrene. Automated dip coating technique was used to obtain ring-shaped coatings with thickness ranging in hundreds of nanometers. The transmission spectra of the obtained devices were collected in order to outline the effects of thickness, tilt angle, and surrounding refractive index. Experimental results reveal interesting differences with respect to the uncoated case, both in terms of spectral envelope and wavelength shifts related to cladding modes coupling. [ABSTRACT FROM PUBLISHER]

In this letter, a demodulation technique is presented in order to measure the surrounding refractive index in the range 1-1.45 by means of a weakly tilted fiber Bragg grating. This technique is based on the global monitoring of the cladding modes in the transmitted spectrum and on the computation of two statistical parameters. We report a resolution of 210-4 in terms of the refractive index as well as a temperature-insensitive behavior. [ABSTRACT FROM PUBLISHER]