Femtosecond laser direct inscription of mid-IR transmitting waveguides in BGG glasses

A detailed investigation of the photo-inscription of waveguides in barium gallo-germanate (BGG, BaO, GeO2, Ga2O3) glass is presented. Upon irradiation of BGG glass samples of different contents of germanium dioxide with a femtosecond laser pulse train, positive refractive index changes are produced over a wide range of exposure conditions. Waveguides with a controllable diameter ranging from 4 to 35 mu m and a maximum index change up to 10(-2) were inscribed. A glass sample with custom molecular composition was purified to remove hydroxyl ions and reduce the strong absorption band near 3 mu m. A careful tailoring of the writing conditions allowed for the inscription of low-loss waveguides supporting only two transverse modes at the wavelength of 2.78 mu m. An upper bound for the propagation losses of 0.5 +/- 0.1 dB/cm was determined, showing the great potential of the BGG glass family for the fabrication of core waveguides operating in the 2-4 mu m spectral range. Our results actually open a pathway towards the integration of mid-IR photonic devices based on the BGG glass family. (C) 2017 Optical Society of America