Dynamics of the Refractive Index Induced in Germanosilicate Optical Fibres by Different Types of UV Irradiation

A Mach-Zehnder fibre interferometer, based on two photoinduced long-period gratings, was used in an investigation of the dynamics of the refractive index Delta n(ind) induced in the core of a germanosilicate optical fibre by different types of UV irradiation, It was found that the value of Delta n(ind) could be approximated satisfactorily by a power-law function of the radiation dose at all the investigated wavelengths. A comparative analysis of the dynamics of the refractive index in the case of singlet and triplet photoexcitation of germanium oxygen-deficient centres showed that the dominant mechanism of the change in the refractive index by low-intensity continuous UV irradiation was transformation of these centres from an excited triplet state.