Ultra-miniature catadioptrical system for an omnidirectional camera

Abstract

The restricted field of view of traditional camera technology is increasingly limiting in many relevant applications such as security, surveillance, automotive, robotics, autonomous navigation or domotics. Omnidirectional cameras with their horizontal field of view of 360° would be ideal devices for these applications if they were small, cost-effective, robust and lightweight. Conventional catadioptric system designs require mirror diameters and optical path lengths of several centimeters, often leading to solutions that are too large and too heavy to be practical. We are presenting a novel optical design for an ultra-miniature camera that is so small and lightweight that it can be used as a key navigation aid for an autonomous flying micro-robot. The catadioptrical system consists of two components with a field-stop in-between: the first subsystem consists of a reflecting mirror and two refracting lens surfaces, and the second subsystem contains the imaging lens with two refractive surfaces. The field of view is 10°(upward) and 35°(downward). A field stop diameter of 1 mm and a back focal length of 2.3 mm have been achieved. For low-cost mass fabrication, the lens designs are optimised for production by injection moulding. Measurements of the first omnidirectional lens prototypes with a high-resolution imager show a performance close to the simulated values concerning spot size and image formation. The total weight of the optics is only 2 g including all mechanical mounts. The system's outer dimensions are 14.4 mm in height, with a 11.4 mm × 11.4 mm foot print, including the image sensor and its casing.