Femtosecond Laser Fabrication of Gradient Refractive Index Micro-Lenses in Chalcogenide Glass for Applications in Visible and Infrared Region

Gradient refractive index (GRIN) lenses are optical components having spatial variations of refractive index in the material [1]. GRIN lenses have been widely used for several applications such as the correction of optical aberrations [2], fiber coupling [3], imaging systems [4]. Many techniques have been developed for the fabrication of GRIN lenses: chemical vapor deposition, ion exchange or neutron irradiation [5]. However, these techniques cannot be applied for all materials because their use depends of the composition [6]. In addition, the femtosecond laser direct writing (FLDW) method is a very flexible technique to modify the refractive index of materials. This powerful method allows controlling the inscribed shape [6], especially in the scale of
$\mu \mathrm{m}$
. In this work, we focus on the fabrication of GRIN micro-lenses in chalcogenide glasses (ChG) using this FLDW method.