Structural modifications in Er-Yb doped phosphate glass induced by femtosecond laser waveguide writing

We have systematically studied femtosecond-laser fabrication of optical waveguides in an Er-Yb doped phosphate glass. Waveguides were written using the IMRA America FCPA mu Jewel D-400 femtosecond fiber laser system with pulse repetition rates ranging from 250 kHz to 2.2 MHz. At every pulse repetition rate a series of waveguides was written while varying scan speeds from 50 mu m/s to 100 mm/s and pulse energies from 80 nJ to 320 nJ. The optical quality of the waveguides was evaluated by measuring the waveguide mode profile as well as the optical loss. Laser-induced defects and structural changes in the glass were characterized using confocal fluorescence and Raman microscopy.