Nonlinear refractive index of ultrafast laser inscribed waveguides in gallium lanthanum sulphide

We demonstrate ultrafast all-optical switching in femtosecond laser inscribed nonlinear directional couplers in gallium lanthanum sulphide operated at 1.55 μm. We report on the evaluation of the nonlinear refractive index of the waveguides forming the directional couplers by making use of the switching parameters. The nonlinear refractive index is reduced by the inscription process to about 4-5 times compared to bulk material.