An upper limit on concentration for any optical device has previously been
derived from the conservation of étendue. In this contribution we derive
more stringent upper limits for the efficiency and the concentration of rotationally
symmetric optical devices that are a consequence of skewness conservation.
If the desired source and target have different skewness distributions, then
losses or dilution or both will limit the performance of the optical system.
We calculate the limiting curve of efficiency versus concentration and provide
a design example that is virtually at this limit. We conjecture that even
rotationally symmetric problems may benefit from asymmetric optical systems.
© 1997 Optical Society of America
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