We design the optical unit for an imaging time-of-flight scanner camera based on partially steerable micro
mirrors. This new class of 3D cameras enables video frame rates and-in conjunction with the accompanying
user software-online real-time selection of regions of interest.
The challenges for the optical design comprise (i) sufficient light collection from close-up objects, (ii) maximizing
optical efficiency for objects at large distances, (iii) reduction of the dynamical range of signal returns
and (iv) minimization of parasitic scattering.
We present a solution based on coaxial beam guidance, where the emitted beam first passes a beam splitter, is
then deflected by a dedicated emission mirror in the center of a point-symmetrical, synchronized arrangement of
five micro mirrors and finally passes a protective spherical glass cover. The mirror assembly is slightly displaced
from the center of the dome in order to establish a secondary focus for parasitic reflections at the inside of the
cover. The light scattered at the target surface which reaches the mirror array is directed towards an assembly
of rhomboid prisms. These prisms reshape the distributed mirror array aperture such that a small lens with high
numerical aperture suffices to focus the light onto a fast, small-area avalanche photo diode, thus maximizing the
acceptance angle of the detector and permissible misalignments of the element mirrors.
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