Waveguide writing in silica glass with femtosecond pulses from an optical parametric amplifier at 1.5 μm

Optical waveguides with a circular small-size core were inscribed in the bulk of fused silica glass by use of focused 1.5 μm femtosecond infrared pulses at 1 kHz repetition rate generated by an optical parametric amplifier. A refractive index difference between core and cladding in excess of 6 × 10−3 was achieved which is as large as that induced by Ti-sapphire laser pulses at 800 nm. The observed higher resistance of the silica against structural damage could allow micro-machining of waveguide structures under a broader range of writing parameters. The great stability of the white light pattern suggests that the filamentation of femtosecond pulses at 1.5 μm plays a major role in the formation of the waveguides. The mechanisms of the induced refractive index change were discussed based on the obtained experimental evidences.