Photosensitivity and optical nonlinearity in arsenic selenide planar waveguides [Invited]

We present the first experimental observation of reversible 1550 nm-induced Bragg gratings and stimulated Brillouin scattering (SBS) in a planar waveguide made of high-index chalcogenide material, arsenic triselenide (As2Se3). The temporary grating is inscribed by the two-photon absorption (TPA)-induced refractive index change along the waveguide, facilitated by the high Fresnel reflection from the chip facet. Furthermore, our SBS measurements reveal a Brillouin gain coefficient gB of 7.14 x 10-10 m/W and a frequency shift vB of 7.8 GHz. The Brillouin linewidth increment vB is measured to be 60 MHz at an input power of 144 mW, which is four times broader compared to As2Se3 fibers. We explain the observed broadening of the linewidth that is attributed to the presence of the photorefractive effect in this platform, which induces a non-uniform refractive index profile along the length of the waveguide. The investigation of photosensitivity and optical nonlinearity in this study holds paramount importance for the realization of reconfigurable nonlinear photonic applications utilizing As2Se3 glasses.