Optical design of a compact continuous zoom MWIR lens for surveillance UAVs

This paper describes an optical design of a compact continuous zoom mid-wave infrared (MWIR) lens for use with today's infrared detector technologies. The developed design is applicable in industries where system size becomes a critical factor, including unmanned aerial systems (UAS), unmanned aerial vehicles (UAV) and drone payloads. By applying optical design principles such as power distribution via element bending, element splitting and aberration balancing, a continuous zoom MWIR lens was successfully designed. It has a focal length range of 20–275 mm, which translates to a magnification ratio of almost 14x. The IR detector type that is compatible with the developed design is a VGA (640 x 512) high operating temperature (HOT) MWIR focal plane array (FPA) having a pixel pitch of 15 μm and an aperture of F/5.5. While a standard MWIR FPA is usually sensitive to a spectral range of 3.7–4.8 μm, a HOT MWIR FPA is responsive to a spectral range of 3.7–4.2 μm. This is also the limits which the optical design discussed in this paper was optimized for. Overall, the continuous zoom MWIR lens managed to maintain its high level of imaging performance throughout the prescription zoom range, all of which is contained within a compact package under 100 mm in length. With its long target detection range, the developed design is highly suitable for surveillance UAV payloads as well as other relevant aerial systems on the market.