Research on development of aspheric diffractive optical element for mid-infrared imaging

The aspheric diffractive lens reduces chromatic aberration in precision infrared optical systems. With the advancement in micro-optics, conventional lenses are replaced by aspheric, diffractive and hybrid surfaces to fulfil the requirements of miniaturized design of optical devices. This paper covers the detailed aspects of hybrid aspheric diffractive optics from design to manufacturing by precision machining. The germanium aspheric diffractive lens is designed using Zemax OpticsStudio® for Medium Wave Infrared (MWIR) range to achieve an aberration-free and diffraction-limited surface. The designed surface is fabricated by the diamond turning process. The developed surface is characterized by profile and diffractive structure quality. The results demonstrate the fabricated lens with a diffractive structure step height error of 0.001 µm and radial position error of 1 µm. A high-quality aspheric diffractive lens is fabricated with 99.57 % diffraction efficiency.