Single-channel waveguides and Y couplers were fabricated in chalcogenide thin films by use of femtosecond laser pulses from a 25-MHz repetition rate Ti:sapphire laser. Refractive-index differentials (Δn>10-2) were measured through interferometric microscopy and are higher than the typical values reported for oxide glasses. The dependence of the index differential on the peak intensity reveals the nonlinear nature of the photosensitivity in arsenic trisulfide below its bandgap energy, and the refractive-index change is correlated to the photoinduced structural changes inferred by Raman spectroscopy data. A free-electron model to predict the parametric dependence of Δn is proposed.
© 2004 Optical Society of America
(220.4000) Optical design and fabrication : Microstructure fabrication
(230.7380) Optical devices : Waveguides, channeled
(320.7130) Ultrafast optics : Ultrafast processes in condensed matter, including semiconductors
(320.7160) Ultrafast optics : Ultrafast technology
Arnaud Zoubir, Martin Richardson, Clara Rivero, Alfons Schulte, Cedric Lopez, Kathleen Richardson, Nicolas Hô, and Réal Vallée, "Direct femtosecond laser writing of waveguides in As2S3 thin films," Opt. Lett. 29, 748-750 (2004)