Design of the diffractive-refractive hybrid lenses in infrared bifocal optical system

In order to meet the demand of low F number and high optical throughput in infrared optic zoom systems with un-cooled detectors, a system is designed by taking advantage of the negative dispersion of diffractive optical elements (DOEs) and the application of the binary optical lenses. The results show that good imaging quality is achieved with only four Germanium lenses. When the system´s focal length is set at either 80mm or 160mm, respectively, the F number remains the value of 1, the image position keeps stable, the RMS is less than 24.2μm, and the total length of the system is less than 236mm. The optic transfer function (OTF) is close to diffraction limitation.