Three dimensional Modification of the Refractive Index in Photosensitive Foturan Glass

We present a new approach for laser induced 3D modification of the refractive index in the volume of Foturan glass. It is based on a direct laser writing process where fs-laser pulses are focused by a microscope objective into the bulk of the glass substrate, which is mounted on high precision 3D translation stages. The laser has a wavelength centered at λ=1550 nm, a repetition rate of 25 kHz and a pulse energy of 40 µJ. With this method a refractive index change of the order of ∆n = 10^(-3)can be achieved through a multiphoton absorption process and subsequent postbaking of the sample at a temperature of 550°C. The method enables integration of 3D micro optical elements. As a proof of concept volume Bragg gratings (VBG) are presented which are fabricated using this novel technique. The refractive index change was verified by means of a DIC microscope and it was shown that smooth internal structures can be achieved. Future work will include fabrication of computer generated volume holograms.