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Modification of Refractive Index with Synchrotron X-rays

Paul Stoddart, Felix Salomon (University of Constance), Peter Cadusch

It is well known that fibre Bragg gratings can be efficiently fabricated by compaction in germanosilica and pure silica fibres with radiation energies above the bandgap at 8 eV. It is perhaps not so well known that X-rays can also induce relatively large refractive index changes in glass by at least two different mechanisms, namely compaction and E' colour-centre formation. To date, synchrotron radiation has not been used for the purpose of fabricating Bragg gratings in germanosilicate optical fibres. However, synchrotron radiation has been used to fabricate gratings in polyimide by exposing the sample through an x-ray mask with a grating pattern [1].

This project aims to establish whether significant refractive index changes and efficient writing of gratings and/or waveguides can be achieved by exposing a variety of different silica glasses to synchrotron X-rays. To date, most studies of photorefractive changes in optical materials have been performed at a relatively small number of accessible wavelengths in the ultraviolet. Synchrotron light sources provide an opportunity to extend these studies through the UV and into the X-ray region.

Irradiated glass

[1]. J. Kobayashi, T. Maruno, T. Ishii, T. Tamamura, and T. Horiushi, "Direct fabrication of polyimide waveguide grating by synchrotron radiation," Applied Physics Letters 73(23), 3336-3338 (1998).