Ultrafast laser processing of refractive index changes in bulk Ge 15 As 15 S 70 chalcogenide glass for photonics applications in the mid-infrared

We study the role of carrier excitation in driving either heat deposition or non-thermal molecular mobility via electronic relaxation in ultrafast laser-irradiated chalcogenide S-based glasses. We show the influence of doping and of the glass thermal history in determining permanent positive and negative refractive index change regimes (type I or type II) discussing the case of Ge 15 As 15 S 70 chalcogenide glass. We also point out material and index engineering approaches in defining large mode area light transport concepts in evanescently-coupled waveguide arrays and their application for building embedded detectors for astronomical measurements.