Radial graded‐index chalcogenide glass lenses for mid‐infrared optics

Abstract Radial graded‐index (R‐GRIN) lens, which has two flat surfaces, is a self‐focusing lens. It can precisely control the beam focusing and simplify the optical system structure, showing great potential in the fields of advanced optics such as optical communication, optical sensing, and optical imaging. Although R‐GRIN lenses working in the visible to near‐infrared waveband have been widely used in fiber optics and microimaging, those operating in the mid‐infrared spectral region have not been commercially available due to the lack of efficient production technology. In this work, mid‐infrared Ge–As–Se–Te chalcogenide GRIN lenses are fabricated by an innovative technique suitable for mass production, and their potential for mid‐infrared optics is assessed. The R‐GRIN lenses are fabricated by assembling a glass rod and a series of glass tubes with gradually changing refractive indices (RIs) into a coaxial preform, drawing it into a cane, cutting the cane into disks, and heat‐treating them. The fabricated R‐GRIN lenses have a diameter of 4.0 mm, a length of 3.86 mm, and an RI contrast of ∼0.238 at 10 µm. The measurement using a 4.6‐µm single‐mode laser as the light source shows that the lenses have a focal length of ∼1.0 mm and can focus the beam with a diameter of 3.3 mm into a spot with a diameter of 0.67 mm. It therefore demonstrates good potential of Ge–As–Se–Te R‐GRIN lenses for mid‐infrared optics and provides a solution for mass production of high‐performance R‐GRIN lenses.