Study On Radiation Resistance Properties Of Silica Glass And Silica Optical Fibre

In recent years, the applications of silica glass and silica optical fibres in the radiation environment aroused extensive attention of the researchers. There are different opinions of the influence of material structure on the radiation resistance properties of silica glass and silica optical fibres. Arguments are never stopped on the radiation-induced defect in different radiation conditions. In this dissertation, the pure silica glass, doped silica glass and optical fibres fabricated with PCVD process are taken as the study objects, in order to further study the radiation-induced defect mechanism and concerned influence factors, to lay a foundation for the production of high quality radiation resistance optical fibres. The dopant influences on the structure of silica glass and radiation resistance properties are researched. The radiation resistance propertiesof optical fibres with different structures are compared. The relationship between radiation-induced losses of optical fibres and radiation conditions is studied. The improvement of optical fibre's radiation resistance properties is considered as well. The main contents and conclusions are as follows:(1) By analyzing the Si-F bond vibration absorption bands from the infra-red spectrum and Raman spectrum of Fluorine doped silica glass, it was found that Fluorine exists in silica networks as the formation of [SiO3F]. The introduction of Fluorine will increase the probability of bond broken, and decrease the structures of 3-fold rings and 4-fold rings. Consequently, the radiation resistance properties of silica glass will be improved with the increase of the Fluorine doped quantity. According to the UV-VIS spectrum combined with ESR test results, the absorptions of the pure silica glass and doped silica glass in 200 to 900 nm are mainly contributed by SiE' centers. In this dissertation, the formation principle of SiE' centers was researched. The functional relation of the SiE'absorbance and radiation dose was explained as well.(2) By analyzing the Raman spectrum of Ge doped silica glass, the Si-O-Si stretching band (1060cm-1), the overlap of bending vibration of Si-O-Si(420cm-1) and Ge-O-Ge(440cm-1) were observed. The vibration band of Ge-O-Si at 675cm-1 were observed as well. It has been proved that the linkage between [SiO4] and [GeO4] in Ge-doped silica glass exists. Based on the two level energy model, the change of 3-fold rings and 4-fold rings band was explained. The radiation resistance properties of silica glass will be deteriorated with the increase of the Germanium doped quantity. After radiation, plenty of Ge-related color centers were found. The Ge-related color centers are mainly located around 193nm,213nm,242nm and 300nm which will cause the absorption increase and permeation decrease in the ultraviolet band. Combined the ESR test results and optical absorption spectrum, the flaws in Ge-doped silica glass were identified. After calculation, it was demonstrated that there is linear relationship between the absorption peak value at 300nm and the Ge(1) center concentration. Besides, no linear relationship was found between the absorption peak value at 213nm and the GeE'center concentration.(3) With the introduction of material structure of silica optical fibre, the advantages of PCVD process used for the fabrication of radiation resistant optical fibre are analyzed. Three kinds of single mode optical fibres with different structures were compared:the pure silica core optical fibre has the best radiation resistance, the F-Ge co-doped optical fibre with functional graded material design takes the second place, and the Ge-doped silica core optical fibre is the worst. Different radiation conditions on the same multimode optical fibres were evaluated as well. Based on the refractive index (RI) test results, it has been proved that even with high radiation dose (10kGy/h×10h), the Gamma irradiation will not influence the waveguide structures obviously. Based on the ESR test results, the transition process of radiation induced defects in optical fibres was researched. Functional relation between the radiation induced losses (SMF at 1550nm and MMF at 1300nm) and radiation conditions was concluded. It could be used for the pre-evaluation of the radiation resistance properties of the optical fibres.(4) The radiation resistance properties are dependent of the drawing process. The pure silica core optical fibre is more sensitive with the drawing process, and the Ge-F co-doped single mode fibre is insensitive with the drawing process, which is more suitable for large scale production. Comparing the effect of hydrogen treatment with that of pre-radiation plus hydrogen treatment, it has been proved that the later is more effective on optimizing the radiation resistance properties of the optical fibre. This is especially meaningful for the image-guide-used optical fibres.