Overview: High-resolution images of an unfocused laser beam were obtained by masking the aperture of an annular folded optic imager. Image processing yielded calibrated distance measurements correlated to the separation of the beam spots.
Numerous mobile applications benefit from range finding technologies, including but not limited to conventional surveying, robotic navigation, and hand-held imagers. Recent surveys in optically based measurement devices detail numerous different techniques [1,2]. The predominant method used commercially is time of flight (TOF) that uses the amount of time required for a light pulse to reflect back to a high-speed receiving detector. Other techniques use multiple frequency phase-shift or a CCD or CMOS imager to interpret laser projections and effects such as speckle sectioning, moiré patterns, and structured lighting. The imaging disadvantage of higher processing requirements comes with the added benefit that these methods can provide direct correlation between pictures and distances as well as measure short ranges, often less than 1m that TOF cannot accomplish inexpensively. This paper leverages recent developments in folded optic imagers to create a CMOS-based range finder that accurately resolves distances while using minimal computational processes. The enabling technology is the application of a pupil mask to a folded optic imager that has an inherently narrow depth of field.