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Microdisplay-based industrial 3-D and microstructure measurement systems
Microdisplays, whether they are of the liquid-crystal-on-silicon (LCOS) or organic light-emitting diode (OLED) type, have been, up until now, mainly used in multimedia applications or head-mounted displays. Due to their interesting possibilities, these displays open more and more alternative applications; for example, in optical metrology. Projection lenses for this application area need to be specially designed because the requirements on these systems differ completely from those for multimedia applications. The lenses must have very low geometrical image distortion and they have to be adapted to small objects and/or image distances. On the other hand, they often work with light sources with small spectral bandwidths; consequently, they do not need to be corrected for chromatic aberrations. In addition, the numerical aperture has to be large enough to collect and transfer as much light as possible, but also the size of the projection lens has to be as small as possible toensure compact measurement systems. All these requirements lead to a compromise in optical lens design. Three optical system designs and realizations - one with an OLED microdisplay and two with an LCOS microdisplay - are presented.