Radiation-induced effects on UV-written LPGs inscribed in B-Ge doped optical fiber for experiments running at CERN

In this contribution, we provide an overview of our recent results concerning the proton radiation-induced effects of a bare Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser. Experimental data collected during an extensive irradiation campaign performed at the European Organization for Nuclear Research (with a fluence of 4.4·1015 p∙cm-2) have been combined with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the high dose proton exposure. A maximal radiation-induced variation of the core effective refractive index of ~1.61·10-4, responsible for a resonance wavelength red shift of ~44 nm, was retrieved at the maximal absorbed dose of 1.16 MGy. At the same time, a relevant decrease of ~0.93·10-4 in the grating refractive index modulation was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The spectral response of the LPG and the optical fiber parameters were analyzed also during the relaxation phase, showing a partial recovery of the wavelength shift due to a decrease of the core refractive index, without any relevant change in the dip visibility as a consequence of the constant grating modulation.