Control of femtosecond laser written waveguides in silica glass

The ideal conditions for writing waveguides in bulk fused silica glass by focused femtosecond laser pulses (810 nm, 1 kHz, 45 fs) are analysed. The thresholds for optical breakdown (OB), single and multiple filamentation (FL), and structural damage are measured as a function of the external focusing conditions. The obtained thresholds map provides a systematic means for writing and characterizing optical waveguides based on pure OB, pure FL, and a combination of both processes. The waveguides written under the OB and FL regimes are showing different features. The formation of multiple filaments at high input powers, based on the use of long focal lengths, is also considered as an alternative method to create various refractive index structures in glass.