Femtosecond Laser Direct Writing of Gradient Index Fresnel Lens in GeS2-Based Chalcogenide Glass for Imaging Applications

Abstract

Chalcogenide glasses have attracted growing interest for their potential to meet the demands of photonic applications in the Mid-Wavelength InfraRed (MWIR) and Long-Wavelength InfraRed (LWIR) transmission windows. In this work, we investigated the photosensitivity to femtosecond laser irradiation of a dedicated chalcogenide glass, along with its possible applications in micro-optics. In order to address the SWaP problem (Size, Weight and Power), this work took advantage of recent techniques in femtosecond laser direct writing to imprint flat and integrated optical systems. Here, we wanted to simplify an infrared multispectral imaging system which combines a lens array and a filter array. Each channel has a focal length of 7 mm and an f-number of 4. We show in this paper that the chosen GeS2-based chalcogenide glass is very promising for the fabrication of graded index optics by fs-laser writing, and particularly for the fabrication of Fresnel lenses. We note a very important phase variation capacity in this infrared material corresponding to refractive index variations up to +0.055. A prototype of Fresnel GRIN lens with a refractive index gradient was fabricated and optically characterized in the Vis range.