PHOTOINDUCED REFRACTIVE INDEX CHANGE AND SECOND HARMONIC GENERATION IN MCVD GERMANOSILICATE CORE FIBRES FABRICATED IN REDUCED (NITROGEN AND HELIUM) ATMOSPHERES

Abstract

Single-mode germanosilicate-core optical fibres were fabricated by the MCVD process modified by sintering of the deposited soot in a reduced atmosphere (helium- or nitrogen-containing one). The fibres showed a higher photoinduced refractive index: change and a higher efficiency of chi ((2)) formation as compared to an ordinary germanosilicate fibre. The sintering process in nitrogen and helium atmospheres was shown to increase the concentration of germanium oxygen-deficient centres. Besides, nitrogen appears to enter into the glass network in a sufficient concentration to modify the glass network and to additionally increase photosensitivity of the fibres.