Refraction index modification by synchrotron radiation

Abstract

Refractive index modifications in glass play an important role in fibre optic communications. One of the more challenging issues in fibre optics has been how to process the light in optical systems while avoiding the losses which are inherent in the process of coupling light out of fibres. Using bulk optics to perform reflection, difraction and filtering, inevitably increases the system complexity and at the same time decreases its performance. Hence there is great interest in developing in-fibre equivalents of devices such as beam splitters, filters or optical mirrors as they would potentially perform this processing more efficiently. Moreover, 'fiberised' devices would increase the stability, reliability and simplicity of fibre optic communications.To date, the common method used to write refractive index structures into glass involves the use of a UV laser source. This method is constrained by a number of restrictions which could possibly be avoided by using the high energy X-ray light of a synchrotron to produce in-fibre devices. Mid last century, researchers performed experiments on the exposure of glass to synchrotron light. This diploma thesis expands on these initial results with the benefit of modern experimental facilities, to investigate the effects of synchrotron radiation on different glass samples and intends to thereby gain a more coherent, fundamental understanding of the effects of synchrotron light.In order to produce appropriate samples, various optical glasses and fibres were taken to the National Synchrotron Radiation Research Center (NSRRC) in Hsinchu, Taiwan, and irradiated with synchrotron light with an energy above 500 eV and a peak energy of 7.8 keV. Tests were subsequently performed to measure the compaction (densification) of the material and possible changes in the refractive index. By means of surface analysis, evidence has been found that compaction occurred and this densification has been quantified. A model for the refractive index modification has been developed and, using ellipsometry, initial measurements have been performed to prove the model.